Dr habil. Tayssir Hamieh, Ph.D. (T.H.)

Research ptojects of Tayssir Hamieh
 

1. Research Project

New approach to characterize the interaction forces between microbial cells and solid surfaces: Effect of the nature of electrolyte and the geometry of solid nanoparticles

 

Key words

Microbial cells, EDL, DLVO, interaction energy, AFM, surface potential, surface charge density, asymmetrical electrolytes, Poisson-Boltzmann equation, Nonspecific Forces

 

Introduction and bibliographic review

Many works were devoted during the last twenty years to study the interaction forces between microbial cells and solid surfaces. Understanding the fundamental forces involved in the adhesion of microbial cells is of crucial importance not only in microbiology, to elucidate cellular functions, but also in medicine (biofilm infections) and biotechnology [1]. Microbial cells show remarkable adhesion properties that are of relevance to medicine and industry. The adhesion of pathogens to surfaces is the primary step leading to biofilm formation and associated infections, but cell adhesion and aggregation are also widely exploited in biotechnology for immobilizing or separating microbial cells. Cell adhesion is mediated by a multitude of molecular interactions that are specific or non-specific [2]. Abu-Lail et al. [3] combined the results of Poisson analysis with the results obtained through soft-particle Derjaguin−Landau−Verwey−Overbeek (DLVO) analysis to determine the contributions of the Lifshitz-van der Waals and electrostatic forces to the overall nonspecific interaction forces. Adhesion forces were then decoupled into specific (hydrogen bonding) and nonspecific (electrostatic and Lifshitz-van der Waals) force components using Poisson statistical analysis [3].

The nature of the physical interactions between Escherichia coli JM109 and a model surface (silicon nitride) was investigated in water via atomic force microscopy (AFM) [4]. An analysis was presented based on the application of Poisson statistics to AFM adhesion data, to decouple the specific and nonspecific interactions. The Poisson statistical analysis of adhesion forces may be very useful in applications of bacterial adhesion, because it represents an easy way to determine the magnitude of hydrogen bonding in a given system and it allows the fundamental forces to be easily broken into their components [4].

Park et al [5] studied the effect of pH conditions of growth in the specificity of interaction forces Measured Between pathogenic L. monocytogenes and silicon nitride the pH of growth media is an important factor in controlling the adherence of L. monocytogenes to inert surfaces due to the altered composition of its surface biopolymers.

A. Vilinska et al. [6] evaluated the adhesion of Leptospirillum ferrooxidans bacterial cells onto the sulfide minerals pyrite and chalcopyrite using two different physical-chemical approaches; thermodynamic and extended DLVO theory. The adhesion of microbes on interfaces and the subsequent formation of biofilms has a large influence on bioengineering processes such as environmental purification, valuable resource production, and bioremediation [7].  Yoshihara et al. [7] estimated the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface, and quantitatively evaluated the effects of the presence or absence of microbial flagella, and the microbial motility on the colloidal behaviors of microbial cells. Zhang et al. [8] studied the retention and transport of an anaerobic trichloroethene dechlorinating microbial culture in anaerobic porous media by calculating DLVO interaction energies and determining their adhesion behavior.

Many researchers were interested in understanding and controlling bacterial adhesion to material surfaces in various disciplines: biomedical, environmental and industrial. Microbial adhesion may lead to the formation of an infectious biofilm that may cause infection on biomaterials and implanted medical devices, contamination of water resources and biofouling in food-processing equipment and in many engineered and marine systems [9]. The DLVO theory has been widely used as a theoretical model not only qualitatively but also quantitatively to calculate the actual adhesion energy variations involved in bacterial (or colloidal) adhesion and aggregation as a function of separation distance between the interacting surfaces [9]. Van Oss et al. suggested an additional term called the short-range Lewis acid–base (AB) interactions to account for hydrogen bonding on close approach of bacteria and substrate surfaces, in an extended XDLVO theory [9].

 

Atomic force microscopy (AFM)

Today, AFM technique allows to determine the force strengths and length scales, ranging from weak intermolecular interactions to strong covalent bonds [1]. Currently, AFM is the only technique that is well-suited for probing forces on microbial cells, both at the single cell and single-molecule levels [1]. AFM measures the forces between a sharp probe (‘tip’) and the sample while scanning over the sample surface [1]. AFM cantilevers and tips are made of silicon or silicon nitride using microfabrication techniques. During the last years, AFM has been used increasingly to investigate microbial surfaces at high resolution. The technique provides three-dimensional images of the surface ultrastructure with molecular resolution, in real time, under physiological conditions, and with minimal sample preparation. AFM is more than a surface-imaging tool in that force measurements can be used to probe the physical properties of the specimen, such as molecular interactions, surface hydrophobicity, surface charges, and mechanical properties. These measurements provide new insight into the structure-function relationships of microbial surfaces [13].

With its ability to observe living microbial cells at nanometer resolution and to manipulate single-cell surface molecules, AFM has emerged as a powerful tool in microbiology for new structural, and functional insights into the microbial cell surface [14]. AFM-based techniques have been increasingly used for the multiparametric analysis of microbial cell surfaces, providing novel insight into their structure-function relationships. The main advantages of AFM for microbiologists are the possibility to image cellular structures at molecular resolution and under physiological conditions, the ability to monitor in situ the structural dynamics of cell walls in response to stress and to drugs, and the capability to measure the localization, adhesion, and mechanics of single cell wall constituents. Unlike other forms of microscopy, AFM operates by sensing the small forces acting between a sharp tip and the sample surface. In addition, AFM force spectroscopy can be used to quantify the forces between the tip and the sample [14].

 

Electrical double layer and Atomic force microscopy

Electrical double layer (EDL) forces develop between charged surfaces immersed in an electrolyte solution. Biological material surrounded by its physiological medium constitutes a case where these forces play a major role. Specifically, this work is focused on the study of the EDL force exerted by DNA molecules, a standard reference for the study of single biomolecules of nanometer size. The molecules deposited on plane substrates have been characterized by means of the atomic force microscope operated in the force spectroscopy imaging mode. The AFM has demonstrated its capability to provide images of biomolecules with high resolution [15]. The measurement and imaging of EDL forces arising between the AFM tip and the sample surface can be improved by combining simultaneously AFM imaging with spatially resolved force spectroscopy. This involves acquiring a force-distance curve at each pixel of a simultaneously acquired AFM topography image. Ruiz-Cabello et al. [16] showed that the colloidal-probe technique, which is based on force measurements made with the atomic force microscope, can be used to accurately determine the charging parameters of water-solid interfaces. Besides yielding accurate values of the double-layer or diffuse-layer potential, the method also allows reliable determination of the charge regulation properties of the surfaces.

In many situations, the underlying interactions involving particles and surfaces can be quantified with the DLVO theory. Double-layer forces are normally described with the Poisson-Boltzmann (PB) theory, or its linearized version, the Debye-Hückel (DH) theory. Double-layer forces depend strongly on the solution composition and the electric surface potential. Moreover, the force profiles are not determined by the potential directly at the surface, which is referred to as the surface potential, but rather by the potential at the plane of origin of the diffuse layer. This potential is called the diffuse-layer potential, double-layer potential, renormalized potential, or the effective potential. The diffuse-layer potential cannot be easily estimated even for the simplest materials, and must be measured. The advent of AFM soon led to the development of the more versatile colloidal-probe technique [16]. This method replaces the sharp AFM tip with a so-called colloidal probe, which consists of a μm-sized colloidal particle that is attached to a tip less AFM cantilever. By attaching colloidal particles to the substrate as well, one can also measure forces between two particles in the sphere-sphere geometry with the AFM.

Ruiz-Cabello et al. [16] proposed a variant of colloidal probe technique that uses a highly charged probe particle with precisely known charging properties.

 

Objectives

While the general understanding of colloidal interactions has developed significantly since the formulation of the DLVO theory, many problems still remain to be solved. One real problem is that the current theory has been developed for interactions between flat and chemically homogenous surfaces, which is in contrast to the surfaces of most natural and manufactured materials, which possess topographical variations.  Further, the geometry of nanoparticles is rather spherical or cylindrical, the presence of asymmetrical electrolytes will complicate the resolution of the Poisson-Boltzmann equation.

We propose in this research project to develop new approach to characterize the interaction forces between microbial cells and solid surfaces by studying the effect of the nature of asymmetrical electrolyte and the geometry of solid nanoparticles on these interaction forces and by combining surface thermodynamics, EDL, DLVO and AFM technique.

The modeling of these forces as well as in correlating with the findings of Abu Lail research works [4, 5, 10] with the physiochemical properties of microbes obtained using contact angle measurements and electrophoresis will be extremely useful to publish several scientific papers.

 

Methodology

First, we will be interested in the development of a new model based on the hypothesis of spherical or cylindrical particles that will be in interaction with microbial cells in presence of dissymmetrical electrolytes. This study will lead to new expressions of the surface potential and surface charge density that will allow to model the electrical double layer and the repulsive interaction energy. These theoretical results will be very useful to interpret the experimental results previously obtained.

In order to determine the interaction energies or forces between bacterial cells and solid substrates, three techniques will be used: contact angle measurements, electrophoresis and atomic force microscopy. The results obtained by Abu Lail et al. [4, 5, 10] will be taken into consideration and modeled following the obtained theoretical results.

In many previous papers [17-27], we studied the interaction energy and forces of particles in dispersion in  liquid media, the Poisson-Boltzmann equation, and more particularly the linearized model initially developed by Debye and Hückel, and applied the results on polyions like the ADN molecules, by supposing an infinite cylinder carrying a charge uniformly smeared over the surface. The stability of concentrated suspensions was also studied and the conditions of the dispersion of coal in water were optimized. The non-linear Poisson-Boltzmann equation was resolved in the case of charged spherical particles in the presence of dissymmetrical electrolytes. A more adapted and precise solution of this non-linear differential equation was given [23, 24]. By studying of the surface potential and charge density of the coal-water suspensions, we confirmed the theoretical results and we resolved an industrial problem in preparing of fluid and stable concentrated suspensions of coal in water [22, 23, 27].

We established the relationships of the electrostatic potential (x) and of the surface charge 0 and demonstrated that electrolytes of trivalent anions (1-3) and (2-3) give higher surface densities [24]. These theoretical results were confirmed by experiment in studying the surface charge and potential of the suspensions of coal in water in the presence of different dissymmetrical electrolytes [23].

Our proposed and solved model of Poisson-Boltzmann equation will allow to calculate the EDL interaction force and energy between spherical or cylindrical particles

The developed and solved Poisson-Boltzmann equation [25] is presented by the following expression:

     

Where  is the surface potential of solid particle, N Avogadro number, Zj = j the valence of ion j, e the electron charge, k the Boltzmann constant, T the absolute temperature and  the permittivity of the liquid.

With , we obtain:

 

Where                                 ,    and

Where 0 is the surface charge density.

The resolution of this differential equation when the bacterial cell is in interaction with the solid particle in presence of asymmetrical electrolytes will allow to obtain both expressions of the surface potential and the surface charge density. The advantages of this approach are following: The new model can be advantageously used for asymmetrical electrolytes and for different geometries of molecules These results will help us to determine and quantify the interaction force between cells and surfaces.

 

References

1. Sticky microbes: forces in microbial cell adhesion Yves F. Dufrêne, Trends in Microbiology, 2015, 23, No. 6, 376-382.
2. Müller, D.J. et al. Force probing surfaces of living cells to molecular resolution. Nat. Chem. Biol. 2009, 5, 383–390
3. F. Pinar Gordesli and Nehal I. Abu-Lail, Combined Poisson and Soft-Particle DLVO Analysis of the Specific and Nonspecific Adhesion Forces Measured between L.monocytogenes Grown at Various Temperatures and Silicon Nitride, Environ Sci Technol. 2012, 46(18):10089-98.
4. Nehal I. Abu-Lail and Terri A. Camesano, Specific and Nonspecific Interaction Forces Between Escherichia coli and Silicon Nitride, Determined by Poisson Statistical Analysis, Langmuir 2006, 22, 7296-7301
5. Bong-Jae Park, Fatma Pinar Gordesli, and Nehal I. Abu-Lail, The Role of pH Conditions of Growth in the Specificity of Interaction Forces Measured Between Pathogenic L. monocytogenes and Silicon Nitride, J. Bionanosci. 2014, 8, 1-12
6. A. Vilinska and K. Hanumantha Rao, Surface thermodynamics and extended DLVO theory of Leptospirillum ferrooxidans cells' adhesion on sulfide minerals, Minerals & Metallurgical Processing, 2011, 28, No. 3, pp. 151-158
7. Yoshihara A, Nobuhira N, Narahara H, Toyoda S, Tokumoto H, Konishi Y, Nomura T., Estimation of the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface, Colloids and Surfaces B: Biointerfaces, 2015, 131 67–72
8. Huixin Zhang, Ania C. Ulrich, Yang Liu, Retention and transport of an anaerobic trichloroethene dechlorinating microbial culture in anaerobic porous media, Colloids and Surfaces B: Biointerfaces, 2015, 130, 110–118
9. Sonia Bayoudh, Ali Othmane, Laurence Mora, Hafedh Ben Ouada, Assessing bacterial adhesion using DLVO and XDLVO theories and the jet impingement technique, Colloids and Surfaces B: Biointerfaces, 2009 73, 1–9
10. Bong-Jae Park, Nehal I. Abu-Lail, The role of the pH conditions of growth on the bioadhesion of individual and lawns of pathogenic Listeria monocytogenes cells, Journal of Colloid and Interface Science, 2011, 358, 611–620
11. Fatma Pinar Gordesli, Nehal I. Abu-Lail, Impact of ionic strength of growth on the physiochemical properties, structure, and adhesion of Listeria monocytogenes polyelectrolyte brushes to a silicon nitride surface in water, Journal of Colloid and Interface Science, 2012, 388, 257–267
12. F. Alejandro Bonilla, Natalie Kleinfelter, John H. Cushman, Microfluidic aspects of adhesive microbial dynamics: A numerical exploration of flow-cell geometry, Brownian dynamics, and sticky boundaries, Advances in Water Resources, 2007, 30, 1680–1695
13. Yves F. Dufrêne, Atomic Force Microscopy, a Powerful Tool in Microbiology, J. Bacteriology, Oct. 2002, p. 5205–5213 Vol. 184, No. 19
14. Dufrêne YF. 2014. Atomic force microscopy in microbiology: new structural and functional insights into the microbial cell surface. MBio. 2014 Jul 22;5 (4) e01363-14.
15. J. Sotres and A. M. Baro, AFM Imaging and Analysis of Electrostatic Double Layer Forces on Single DNA Molecules, Biophysical Journal, Volume 2010, 98, 1995–2004
16. F. Javier Montes Ruiz-Cabello, Gregor Trefalt, Plinio Maroni, and Michal Borkovec, Electric double-layer potentials and surface regulation properties measured by colloidal-probe atomic force microscopy, Physical Review E, 2014, 90, 012301
17. T.  Hamieh, J. Toufaily and H. Alloul, Physicochemical Properties of the Dispersion of Titanium Dioxide in Organic Media by Using Zetametry Technique, J. Dispersion Science Technology, JDST, 2008, 29 (9), 1181-1188.
18. T. Hamieh, M. Rageul-Lesouet, M. Nardin, M. Rezzaki et J. Schultz, Study of specific interactions between some metallic organic model molecules, J. Chim. Phys., 1997, 94, 503-524. .
19. T. Hamieh, M. Rageul-Lesouet, M. Nardin, H. Haidara et J. Schultz, Study of acid-base interactions between some metallic oxides and model organic molecules, Colloids and Surfaces A,
20. T. Hamieh, Surface charge density and potential of coal liquid mixtures and controls of their stability and fluidity, J. Mat. Sci., 1996, 31, 5665-5669.
21. T. Hamieh, M. Rageul-Lesouet, M. Nardin et J. Schultz, Etude des propriétés superficielles de quelques oxydes métalliques par chromatographie gazeuse inverse et par zétamétrie en milieux aqueux et organique, J. Chim. Phys., 1996, 93, 1332-1363.
22. T. Hamieh and B. Siffert, Theoretical and practical study of a stability test: application to highly concentrated coal suspensions, Advanced Powder Technol., 1994, 5(2), 143-160.
23. T. Hamieh and B. Siffert,  Theoretical and Experimental Study of the Surface Charge Density and Surface Potential of Coal-Water Suspensions in Dissymmetrical Electrolytes, Colloids and Surfaces, 1994, 84, 217- 228.
24. T. Hamieh and B. Siffert, Calcul du potentiel et de la densité de charge de surface d’une sphère chargée en présence d’électrolytes dissymétriques, J. Chim. Phys., 1992, 89, 1799-1834.
25. T. Hamieh and B. Siffert, Interactions between particles in suspension: application to coal-water suspensions, J. Chim. Phys., 1991, 88, 537-542.
26. T. Hamieh and B. Siffert, Determination of point of zero charge and acid-base superficial coal groups in water, Colloïds and Surfaces, 1991, 61, 83-96.
27. B. Siffert and T. Hamieh, Effect of mineral impurities on the charge and surface potential of coal: application to obtaining concentrated suspensions of coal in water, Colloids and Surfaces, 1989, 35, 27-40.

 

 

1. Research Project

Characterization of superficial physicochemical properties of materials by inverse gas chromatography (IGC) at infinite dilution

 

IGC at infinite dilution is a powerful technique widely used to study surface properties of adsorbents, oxides, cellulose starches or other polymers and polymers adsorbed on metals or oxides.

In many previous studies [1-3], we used inverse gas chromatography (IGC) to characterise the surface characteristics of various oxides and polymers, especially, their surface energies and their interactions with some organic molecules. In this paper, we used IGC technique at infinite dilution [4] on some oxides like, Monogal, MgO, ZnO, SiO2 and Al2O3 carbon fibres, PMMA/alumina and PMMA/silica systems that are known to interact strongly through acid-base interactions and ionic bonds [5].

On the other hand, it is obvious that the polymer properties extremely depend on the temperature. Polymers can be easily affected by abrupt variations of the temperature. In fact, such modifications would induce modifications in the chain segment mobility of polymers. These changes in mobility arising at the glass transition temperatures (Tg) of bulk polymers can be determined advantageously by using IGC technique [6-12]. Some of these polymers can be used in food science for packaging and/ or protection. The interactions between some food and packaging can be also studied by IGC at infinite dilution.

The interest for IGC in food science is increasing in particular when a humidity control is available. For example, the chewing gum polymers give the opportunity to transfer IGC methodology into food science. Gas–liquid chromatography (GLC) was used for the determination of solubility parameters of synthetic polymers such as poly(dimethylsiloxane) and poly(methylmethacrylate) [13]. Price and Guillet and co-workers [3, 9–13] were the pioneers in the physico-chemical interpretation of GLC data from polymers. Pawlisch [24] [14], Macris [15] and Danner and co-workers [16,17] used GLC for purposes going from thermodynamic parameters to diffusion coefficient by capillary IGC. In food science, King and List [18] used GLC to study the interactions of several volatile compounds in soybean oil. Boutboul [19], Delarue and Giampaoli [20], and Boutboul et al. [21] were able to characterise the type of interactions (London,Van der Waal’s dipole–dipole or H-bonding) between starch and several flavour molecules. Gauthier et al [22] showed that attractive or repulsive forces could be calculated from IGC data. Bencze´di and Tomka [23– 25] calculated thermodynamic parameters characterizing water–starch interactions by IGC and developed an equation calculating the solubility parameter of starch using only water as solvent and described the physico-chemical characterization of two different chewing gum bases and the interactions with the incorporated flavour molecules using inverse gas chromatography as a specific technique [26-36].

 

Boutboul et al. [37] studied the interactions between aroma compounds and native corn starch were studied by inverse gas chromatography (IGC). A system of humidification of the carrier gas has been set up and generated a fixed and stable relative humidity of 56.3%. The IGC system worked under pressure (2.1 bars), using starch as stationary phase without any support. This technique allowed to maintain the starch matrix with a constant water content of 10%. The specific retention volumes of volatiles (1-hexanol, 2-hexanol, octanal, ethyl hexanoate and d-limonene) were measured under dry and humid conditions. Retention was higher under humid conditions, especially for 1-hexanol. Retention indices of volatiles with various functions and carbon chain lengths were determined on starch and compared to RI on Carbowax. RI on starch increased with the carbon chain length, like on Carbowax. Retention on starch and Carbowax followed the same general order, relative to the functional group.

It is known that interactions between aroma compounds and food components play an important role in the perception of flavour. Knowledge of these interactions is useful in improving the process and the flavouring of food products [38]. Carbohydrates, particularly starch, are present in many low-water content foods, like cereal-based products. They are also widely used as solid support for aroma compounds [39], and as fatreplacers [40].

Buckton and Gill [41] studied the importance of surface energetics of powders for drug delivery and the establishment of inverse gas chromatography. Powders used here are complex systems with more than one value for surface energy. The presence of different faces, defects, physical forms and impurities will alter the surface properties. There are few good ways to measure powder surface energies, with vapour sorption, especially inverse gas chromatography (IGC) being a logical choice. The significance of surface energy is reviewed briefly, as is the difference between contact angle and IGC data. The utility of IGC for studies of batch to batch variability and some issues relating to finding a suitable number to describe a complex range of surface energies are discussed. The utility of IGC in studies of the amorphous state is shown, where there is value in being able to monitor molecular mobility thresholds, glass transition, collapse and crystallization, as well as relaxation and its impact on surface energy. The conclusion is that the complexity of powders means that scientists should not expect simple correlations between measurements and performance, but that correlations are likely to be there if the correct data are recorded in the most appropriate way [41, 42].

 

Also the study of surface properties of powders used in food or in pharmaceutical industries can be expected to provide data that will at worst explain batch to batch variability, and at best provide control for approaches such as inverse gas chromatography, because it is logical that surface science of powders will be a factor to consider and thus vital to understand how surface properties may best be measured for powders used in food or in pharmaceutical industries. Inverse gas chromatography (IGC) is becoming well known in the pharmaceutical sector, although publications have only started in this field in the early 1990s [43], the technique was already well established in other disciplines and the subject of a number of books [44–48].

 

Gamelas et al. [49] recently studied the surface properties of distinct nanofibrillated celluloses by inverse gas chromatography. The adhesion and surface properties of nanocelluloses are an important issue to consider when using this material for composites production, in food packaging or coatings, as well as for determining the influence of added functional groups. In their recent paper Gamelas et al. [49] studied the surface properties of two nanofibrillated celluloses obtained by mild 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation with distinct mechanical treatment intensity in a homogenizer (5 and 15 passes), and one nanofibrillated cellulose obtained by enzymatic process, using the inverse gas chromatography at infinite dilution. The dispersion component of the surface energy gsd was 42–46 mJ m−2 at 40◦C for the TEMPO nanofibers and 52 mJ m−2 for the enzymatic nanocellulose. It was confirmed, based on the determination of the specific components of the works of adhesion and enthalpies of adsorption with polar probes, that the surfaces of the materials have a more Lewis acidic than Lewis basic character [50].

It is well-known that the surface properties of solid materials and the dispersive component of the surface energy can be determined by inverse gas chromatography technique that can also allow to obtain the adsorption thermodynamic parameters as specific components of the free energy, enthalpy and entropy of adsorption, Lewis acid–base character of the surface, surface nanoroughness parameter, etc. [51-54]. Thus, using IGC, a cellulosic fibrous material can be thoroughly characterized with respect to its surface chemical properties. Besides, this technique is advantageous over the classical contact angle measurements for the analysis of porous, rough, heterogeneous and hydrophilic surfaces. Some recent papers reported the use of IGC to analyze nanocellulose [55–59]. In particular, under infinite dilution conditions, the dispersion component of the surface energy was determined for cellulose nanofibers obtained by enzymatic pre-treatments [55] and cellulose nanofibers extracted from hemp fiber by acid hydrolysis and mechanical treatment [56]. For the latter, the Lewis acid–base characteristics were also assessed. The influence of the drying method on the surface energy of cellulose nanofibrils was also evaluated [58]. Gamelas et al. [49] used two nanofibrillated celluloses obtained from an eucalypt bleached kraft pulp by NaClO/TEMPO/NaBr pre-oxidation with distinct mechanical treatment intensity, and one nanofibrillated cellulose obtained by enzymatic process, were thoroughly analyzed for their surface properties by inverse chromatography.

In food sciences, polymers have become one of the main alternatives as materials for the manufacture of food packages; their wide versatility makes feasible the design of suitable containers to fulfil the requirements of every food stuff [59]. However, most of these packages are very difficult to recycle or re-use, generating huge volumes of residues. For this and other reasons, food packaging industry is starting to substitute the traditional polymeric materials for biodegradable ones. The number of biodegradable polymers tested in laboratories is huge, although only a few of them are already used in commercial food packaging applications. The poly(lactic acid)(PLA) and the polycaprolactone (PCL) are among this selected group. Nowadays, the PLA is already commercially used as a substitute of PET in the design of rigid (or semi-rigid) containers. PCL, generally used as additive to ease the process ability of other polymers, is also starting to be used by itself in some applications competing with polyolefins. The PLA is an aliphatic polyester usually synthesized via polymerization of lactic acid, which is mainly derived from corn or whey [60]. Due to its ability to be degraded and assimilated inside the human body within a few months, its first applications were in the biomedical field [61–64]. Recently, due to a decrease on its costs of production, its introduction in the food packaging industry has become possible. In contact with water, it slowly degrades by hydrolysis, delimiting its application to short self-life containers as drinking cups, salad containers and blisters [65]. On the other hand, the oil-derived PCL cannot be degraded by water, but bacteria only need a few weeks to compost it [66]. This semi-crystalline polyester, manufactured by ring-opening polymerization of ε-caprolactone, is characterized by its low melting and glass transition temperatures, as well as by its high elongation at break, low modulus and chain flexibility [67]. The latter properties make it suitable for the production of non-rigid containers or bags.

During the last years, lots of research have been addressed to the improvement of the properties of polymeric materials by loading them with small amounts of dispersed or exfoliated clays, obtaining micro- or nanocomposites. Just by adding the clay particles to the polymeric matrix, properties like its fire ignition resistance are improved, but the dispersion of the particles and its adhesion to the polymer are also needed to improve the mechanical properties and the gas barrier performance of the resulting materials [67–70]. However, the latter situation is not usually obtained in a spontaneous way, and both surfaces need to be modified in order to increase its compatibility and miscibility. Similar comments are valid for the development of composites with biodegradable fibers. In these materials, natural fibers and nanofibers from diverse plant origins are used, instead of synthetic fibers, to reinforce polymeric materials. Besides the development and improvement of polymeric materials, many other properties of plastic packages depend upon adequate surface characteristics, such as printability, surface adhesion in lamination and coextrusion of structures, compatibility with the packed product, especially with foodstuff, and adhesion of microorganisms to food package surfaces. One technique able to characterize the surface of both, polymers and clays, and therefore suggest which surface modifications are required to obtain this outstanding materials is inverse gas chromatography (IGC) [71,72].

Inverse gas chromatography (IGC) is capable to characterize the surface properties (surface energy, heat of adsorption, and specific interaction of adsorption) of materials [73] and recently pharmaceuticals [74-77]. IGC is a real source of physiochemical data [78]. It can be applied to observe the interaction between polymers and organic solvent systems under the conditions approaching infinite dilution of the volatile component [79]. It can be also used to determine the glass transition temperature (Tg) of polymers or amorphous pharmaceuticals and to study the plasticizing effect of water on these materials [80]. This technique is adequate to determine the Lewis acid-base properties of thermoplastic and thermosetting polymer insulating materials [81] or to analyze the area of cellulosic multipurpose office paper [82]. Many other studies were devoted to conducting polymers by Al Saigh and al. [83, 84], and Boukerma and al. [85] and Bailey and al. [86]. ICG is also used to determine the solubility parameters of some solid surfaces as titanate modified silica gel [87] or to compare the surface energies of crystalline, amorphous, and ball milled lactose [88], also to determine the heterogeneous surfaces [89] and textile their products and physicochemical properties [90] ,and to determine  surface energy and surface area of powdered materials [91,92].

The ICG technique is able to analyze the solvent-solvent interactions [93], the surface properties of clays [94, 95], nanomaterials and clay-polymer composites [96, 97], nanoparticles with respect to their specific surface area, particle size and morphology [98], pharmaceutical and food products.

 

In this project, we are interested in the determination of superficial physiochemical properties of some materials, more particularly the determination of surface energy, specific free enthalpy of adsorption of organic molecules and solid substrates, the specific enthalpy and entropy of interactions, the acid-base constants in Lewis terms. We will study also the effect of humidity of the medium on the interaction properties of food packaging.

 

We give below some details on the inverse gas chromatography technique (IGC):

 

Methods of IGC

For over 30 years, inverse gas chromatography has been used to determine the superficial phenomena, glass transitions and acid-base properties of solid materials [99]. We applied this technology to determine the changes, as a function of temperature, of the superficial properties of some polymers and polymers adsorbed on oxides. Probes of known properties are injected into the column containing the solid. The retention times of these probes, measured at infinite dilution, allow us to determine the interactions between model organic molecules and the solid, if we assume there is no interaction between the probe molecules themselves. Measurements were carried out with a DELSI GC 121 FB chromatograph equipped with a flame ionization detector of high sensitivity. The data retention was obtained with a stainless steel column 15-30 cm long and 2 mm internal diameter packed with 1-2 g of solids in powder or fibre forms.

 

Retention volume

The net retention volume Vn which serves to determine the thermodynamic quantities, it is the volume of carrier gas through the column since the introduction of the probe until the output of the maximum of the peak of the inferred methane retention volume V0. It is influenced by the retention time according to the following relation:

Vn = Dc (tr – t0)                                                                  (1)

With Dc representing the corrected of the carrier gas given by the following equation (2). The flow rate correction is given by:

   Dc = j Dm (1+  )                                                       (2)

 

Dm is the measured flow rate of the carrier gas with the bubble flow meter at the outlet of the column. Tc and Ta are respectively the column temperature and the ambient temperature at the time of flow measurement, Patm et PH2O are respectively the atmosphere pressure at the time of analysis and the saturation vapour pressure of water at Ta.

The coefficient j for James Martin [100] takes account of the compressibility of the gas in the column under the action of the charge loss ΔP in the column:

                                                  3 (1 +) 2 -1

 J =                                                                                                              (3)                                                                                                                                                               

                                                    2 (1+) 3-1

 

This coefficient is always less than or equal to 1 [101].

The specific retention volume Vg is also used; it can report the net retention volume to the unit mass of adsorbent and to the temperature 0˚C:

 

  Vg =                                                                        (4)

 

Method of Papirer et al.

Many methods were used to determine the specific interactions exchanged between polar molecules and a solid surface and then obtain the acid- base interactions [73-77, 102-107].

Papirer and al. developed the method giving the more precise specific free enthalpy of interaction between a probe and a solid [102-104]. When plotting RTlnVn against lnP0, Papirer et al have obtained a straight line, where P0 is the vapour pressure of the probes. For a homologous series of n-alkanes (from n-pentane C5 to n-decane C10), Papirer and al. wrote the following equation:

RT ln Vn =A ln P0 ‏ + B                                       (5)

Where A and B are constant depending on the nature of the solid substrate. If polar probes (as for example Toluene) are injected into the column, specific interactions are made between these probes and the solid surface and G0 is now given by:

                                      ΔGo = ΔGd   + ΔGSP                                                             (6)

We can deduce the various values of the free specific enthalpy ΔGSP of the polar molecules at different temperatures, by using Papirer and al. approach.

Then by plotting ΔGSP of the polar molecules as a function of the temperature from the equation:               

ΔGSP = ΔHSP -T ΔSSP                                             (7)

We can deduce the specific enthalpy (ΔHSP) and entropy (ΔSSP) of interaction between the copolymer and the polar molecules.

Determining ΔGaSP at different temperatures is used to draw the straight line of variation of ΔGaSP in function of T. The slope of this line is equal to ΔSaSP and intercepts to ΔHaSP.

 

The method of Guttmann

Inverse gas chromatography is used to evaluate Lewis type acid- base interactions, exchanged between a solid surface and polar molecules. Guttmann [108] classified the polar molecules by assigning an electron donor (ND) and a number of electron acceptor (NA) which realizes respectively the acidity and the basicity of the molecule. In analogy to the approach of Guttmann, Papirer and al [109]   proposed to characterize the solid by two parameters KA and KD respectively reflect the basic and the acidic character of the solid. These two constant measure the ability of the solid to develop respectively the acid and base interactions with basic, acidic or amphoteric probes. They are connected to the specific enthalpy ΔHaSP through the following equation:

- ΔHaSP = KA.ND + KD.NA                                           (8)

Where KA and KD respectively represent the acidic and the basic character of the solid and NA and ND represent the donor number and the electron acceptor of the probe according to the scale of Guttmann [108].

Equation 8 can be written as:

                          KA+ KD                                             (9) 

 

The representation of  in function of   gives in general a straight line of slope KA and intercept KD.

 

 

Description of the chromatography in gas phase apparatus.

The chromatography apparatus is composed of several parts:

 

a-injector: this is the part where the mixture of analytes were injected and evaporated . to facilitate its passage from the injector to the column (also called kiln),the inlet temperature must be higher than that of the furnace. The injection is done by using a micro syringe.

 

b-the column: it is formed from a solid support and a tube of stainless steel, glass or Teflon (for the analysis of corrosive products). When it passes from the injector to the column, the mixture of the analyte migrates there through with a carrier gas (inert gas in the column) and the individual products are separated according to their molecular weight (the lighter get out of the column first) or to their polarity (if the column is polar ,it will retain the polar product longer than the apolar or weakly polar product and the latter (non polar product and weakly polar ) get out first from the column .if the column is apolar the reverse will happen.

 

c-the detector: at the outlet of the column the products pass into a detector where they are analyzed. Since separated, each product gives a signal in the form of a peak (Gauss). The surface of this peak is proportional to the mass or volume concentration of the product in the mixture.

 

 

New model (Hamieh et al. model) [107]

IGC allows to give the retention volumes obtained from different probes (n-alcanes and polar). These volumes allow the determination of RTlnVn values of different polar probes (figure 5) as well the determination of the values of their specific interactions ΔGSP representing the difference between the value of RTlnVn and the corresponding point to its projection on the axis of RTlnVn=f(log Po).

Once ΔGSP is determined for different temperatures it is possible to trace its variation in function of the temperature. A straight line can be obtained and whose slope gives the value of ΔHSP and by the intercept we get -ΔSSP.

The obtained value of ΔHSP is used to determine the values of KA and KD (in our case this equation is treated using the classical model and the model of Hamieh [106, 107]   it is recalled here that the classical model is given by :

- ΔHSP = KA.ND+KD.NA                                            (11)

With NA and ND the electron acceptor and donor numbers, respectively.

While Hamieh’s model [107] corrected the relationship (11) and proposed a new relationship by adding a third parameter K reflecting the amphoteric character of the oxide or polymer according to:

 (- Hsp) = KA DN + KD AN – K DN AN                                            (12)

By dividing by AN, we obtain:

                                           (13)

Equation (13) can be symbolically written as:

X1 = KD + KA X2 - K X3                                               (14)

Where                     ,,  and K = K(KA,KD)

X1, X2 and X3 are known for every polar molecule, whereas KD, KA and K are the unknown of the problem.

     By using N probes, relationship (14) will allow us to write the following equations:

                                  (15)

             (16)

             (17)

One obtains a linear system given by the equations (15-17) at three unknown numbers: KD, KA and K. The matrix representing this linear application is a symmetrical one; we deduce that the problem (15-17) has a unique solution for N ³ 3. We can apply this method to calculate the acid-base constants of our solid substrates. 

 

Determination of the surface energy of solids

The dispersive component of the surface energy of solids  gsd was determined by using the well-known relationship of Fowkes expressing the geometric mean of the dispersive components (exponent d) of the surface energy of the probe gld and the solid  gsd  :

DGo = DGd   = NaWa = 2Na(gld gsd) 1/2                              (18)

where Wa is the energy of adhesion, N is Avogadro’s number and a the surface area of one adsorbed molecule of the probe .

By plotting RTlnVn as a function of 2Naof n-alkanes, we can deduce, from the slope of the straight line, the value of dispersive component of the surface energy of the solid. 

 

References

 

1. Hamieh T, Rageul-Lescouet M,  Nardin M et Schultz J (1996), J. Chim. Phys. 93,  1332-1363.
2. Hamieh T, Rageul-Lescouet M,  Nardin M, Haïdara H, Schultz J (1997), Colloids and Surfaces A: Physicochemical and Engineering Aspects, 125, 155-161.
3. Hamieh T, Rezzaki M,  Grohens Y and Schultz J (1998), J. Chim. Phys. 95,  1964-1990.
4. Conder JR, Young CL (1979), Physical measurements by gas chromatography. J. Wiley and  Sons, New York.
5. Van Alsten J.G, Sauer B.B., Walsh J, (1992), Macromolecules, 25, 4046-4048.
6. Saint Flour C, Papirer E (1982), Ind. Eng. Chem. Prod. Res. Dev.  21, 2, 337-341.
7. Saint Flour C, Papirer E (1982), Ind. Eng. Chem. Prod. Res. Dev.  21, 4, 666-669.
8. Papirer E, Vidal A and Balard H (1989), Analysis of solid surface modification. P. 248-261 in  Inverse Gas Chromatography: Characterization of Polymers and Other Materials, ACS Symposium Series 391, Lloyd D.R., Ward T.C. and Schreiber ed., Washington.
9. Gutmann V (1978), The Donnor-Acceptor Approch to Molecular Interaction. Plenum Press, New York.
10. Siffert B, Kuczinski J and Papirer E (1990), J. Colloid. Interface Sci. 135, 1, 107-117.
11. Fowkes FM  (1964), Ind. Eng. Chem. 56, 12, 40-52.
12. Schultz J, Lavielle L, Martin C (1987),  J. Chim. Phys. 87, 2, 231.
13. G .J. Price, J.E. Guillet, J. Solut. Chem. 6 (1986) 605.
14. K .B. de Roos, Flavour Sci. Technol. (2002) 355
15. W .W. Lee, Pharm. Technol. On-Line (2001) 1. 16.
16. J . Bronislaw, Patent WO 99/44436, 1999.
17. P . Schmiedel, M. Jekel, Patent EP01/08279(C03K), 2002.
18. A .J. Ashworth, G.J. Price, Macromolecules 19 (1986) 358.
19. G .J. Price, J.E. Guillet, J. Solut. Chem. 16 (1987) 605.
20.   G . DiPaola-Baranyi, J.E. Guillet, Macromolecules 11 (1978) 228.
21.   J .E. Lipson, J.E. Guillet, in: R.B. Seymour, G.A. Stahl (Eds.), Macromolecular Solutions. Solvent–Property Relationships in Polymers, Pergamon Press, New York, 1980.
22.   D .G. Gray, J.E. Guillet, Macromolecules 7 (1974) 244.
23.   J .M. Braun, J.E. Guillet, Adv. Polym. Sci. 27 (1976) 107.
24.  C .A. Pawlish, PhD thesis, University of Massachusetts, Amherst, MA, 1985.
25.   A . Macris, MS thesis, University of Massachusetts, Amherst, 1979.
26.   I . Hadj Romdhane, R.P. Danner, AIChE J. 39 (1993) 625.
27.   I . Hadj Romdhane, R.P. Danner, J.L. Duda, Ind. Eng. Chem. Res. 34 (1995) 2536.
28.   J .W. King, G.R. List, J. Am. Oil Chem. Soc. 67 (1990) 1.
29.   A . Boutboul, Dissertation, Paris XI Orsay, 2001.
30.   J . Delarue, P. Giampaoli, J. Agric. Food Chem. 48 (2000) 2372.
31.   A . Boutboul, P. Giampaoli, A. Feigenbaum,V. Ducruet, Food Chem. 71 (2000) 387.
32.   H . Gauthier, A.-C. Coupas, P. Villemagne, R. Gauthier, J. Appl. Polym. Sci. 69 (1998) 2195.
33.   D . Benczédi, I. Tomka, F. Escher, Macromolecules 31 (1998) 3055.
34.   D . Benczédi, I. Tomka, F. Escher, Macromolecules 31 (1998) 3062.
35.   D . Benczédi, Trends Food Sci. Technol. 9 (1999) 1.
36.  Brigitte Niederer, Anh Le, Ennio Cantergiani,, Journal of Chromatography A, 996 (2003) 189–194
37. Boutboul, P. Giampaoli , A. Feigenbaum , V. Ducruet, Food Chemistry 71 (2000) 387-392
38. Dubois, C., Lubbers, S., & Voilley, A. (1995). Industries Alimentaires et Agricoles, 112, 186-193.
39. Goubet, I., Le Quere, J. L., & Voilley, A. J. (1998). Journal of Agricultural and Food Chemistry, 46, 1981-1990
40. Godshall, M. A. (1997). Food Technology, 51(1), 63-67
41. Graham Buckton, Hardyal Gill, Advanced Drug Delivery Reviews 59 (2007) 1474–1479
42. M. Rillosi, G. Buckton, Pharm. Res. 12 (1995) 669–675.
43. [11] Djordjevic, G. Rohr, M. Hinterleitner, B. Schreiber Int. J. Pharm. 81 (1992) 21–29.
44. [12] J.R. Conder, C.L. Young, Physicochemical Measurement by Gas Chromatography, Wiley-Imterscience, Chichester, 1979.
45. [13] R.J. Laub, R.L. Pecsok, Physicochemical Applications of Gas Chromatography, Wiley_interscience, New York, 1978.
46. [14] D.R. Lloyd (Ed.), Inverse Gas Chromatography, American Chemical Society, Washington DC, 1989.
47. [15] O. Planinsek, G. Buckton, Inverse gas chromatography: considerations about appropriate use for amorphous and crystalline powders, J. Pharm. Sci. 92 (2003) 286–1294.
48. [16] V. Gutmann, The Donor-acceptor Approach to Molecular Interactions, Plenum, New York, 1978.
49. José A.F. Gamelas∗, Jorge Pedrosa, Ana F. Lourenc¸ o, Paulo J. Ferreira, Colloids and Surfaces A: Physicochem. Eng. Aspects 469 (2015) 36–41
50. H. Kangas, P. Lahtinen, A. Sneck, A-M. Saariaho, O. Laitinen, E. Hellén, Nord. Pulp Paper Res. J. 29 (2014) 129–143.
51. J.M.R.C.A. Santos, J.T. Guthrie, Mater. Sci. Eng. R50 (2005) 79–107.
52. J.A.F. Gamelas, Cellulose 20 (2013)2675–2693.
53. P. Mukhopadhyay, H.P. Schreiber, Colloids Surf. A 100 (1995) 47–71.
54. J.A.F. Gamelas, E. Ferraz, F. Rocha, Colloids Surf. A 455 (2014) 49–57.
55. N. Siddiqui, R.H. Mills, D.J. Gardner, D. Bousfield, J. Adhes. Sci. Technol. 25 (2011)709–721.
56. B. Wang, M. Sain, Bioresources 2 (2007) 371–388.
57. M. Pommet, J. Juntaro, J.Y.Y. Heng, A. Mantalaris, A.F. Lee, K. Wilson, G.Kalinka, M.S.P. Shaffer, A. Bismarck, Biomacromolecules 9 (2008) 1643–1651.
58. Y. Peng, D.J. Gardner, Y. Han, Z. Cai, M.A. Tshabalala, J. Colloid Interface Sci. 405 (2013) 85–95.
59. D. Cava, R. Gavara, J.M. Lagaréon, A. Voelkel, Journal of Chromatography A, 1148 (2007) 86–91
60. V.K. Holm, S. Ndoni, J. Risbo, J. Food Sci., 71 (2006), p. E40
61. C.G. Pitt, M.M. Gratzl, G.L. Kimmel, J. Surles, A. Schindler, Biomaterials, 2 (1981), p. 215
62. P. Mainil-Varlet, R. Curtis, S. Gogolewski, J. Biomed. Mater. Res., 36 (1997), p. 360
63. N.C. Bleach, K.E. Tanner, M. Kellomaki, P. Tormala, J. Mater. Sci.: Mater. Med., 12 (2001), p. 911
64. H. Tsuji, K. Sumida, J. Appl. Polym. Sci., 79 (2001), p. 1582
65. R. Auras, B. Harte, S. Selke, J. Appl. Polym. Sci., 92 (2004), p. 1790
66. C.D. Kesel, C.V. Wauven, C. David, Polym. Degrad. Stab., 55 (1997), p. 107
67. S. Sinha Ray, M. Bousmina, Prog. Mater. Sci., 50 (2005), p. 962
68. M. Alexandre, P. Dobuis, Mater. Sci. Eng., 28 (2000), p. 1
69. G. Gorrasi, M. Tortora, V. Vittoria, D. Kaempfer, R. Mülhaupt, Polymer, 44 (2003), p. 3679
70. J.C. Grunlan, A. Grigorian, C.B. Hamilton, A.R. Mehrabi, J. Appl. Polym. Sci., 93 (2004), p. 1102
71. D.M. Ansari, G.J. Price, Polymer, 45 (2004), p. 1823
72. E. Fekete, J. Móczo, B. Pukánszky, J. Colloid Interface Sci., 269 (2004), p. 143
73. HP. Schreiber DR.  Lloyd, American Chemical Society, Washington (1989) 1.
74.    D. Cline, R. Dalby, Pharm Res 19 (2002) 1274.
75.     J. C. Feeley, P. York, B. S. Sumby, H. Dicks, Int J Pharm 172 (1998) 89.
76.    M. D. Ticehurst Ph.D. thesis, University of Bradford, York (1995).
77.    G. Buckton, Adv Drug Delivery Rev 26 (1997) 17.
78.   A. Voelkel, B. Strzemiecka, K. Adamska, K. Milczewska, J. Chromatogr A 1216 (2009) 1551.
79.   M. Tazaki, R. Wada, M. Okabe, T. Homma,  Polym Bull 44 (2000) 93.
80.   R. Surana, L. Randall, A. Pyne, N. M. Vemuri, R. Suryanarayanan, Pharm Res 20 (2003) 1647.
81.   S. Baoli, Z. Qianru, J. Lina, L. Yang, L, Bin, J Chromatogr A 1149 (2007) 390.
82.   J. Santos, H. Gil, A. Portugal, J. T. Guthrie, Cellulose 8 (2001) 217.
83.   A. Al-Ghamdi Z. Y. Al-Saigh, J Chromatogr A 969 (2002) 229.
84.   R. Wu, D.  Que, Z. Y. Al-Saigh, J Chromatogr A 1146 (2007) 93.
85.   K. Boukerma, M.  Micˇusˇı´k, M. Mravcˇa´kova´, M. Omastova´, M. J. Vaulay, P. Beaunier, N. M. Chehimi, Colloids Surf A 293 (2007) 28.
86.   R. A. Bailey, K. C. Persaud, Anal Chim Acta 363 (1998) 147.
87.   A. Voelkel, T. Grzeskowiak, Chromatographia 51(2000) 608.
88.   H. E. Newell, G. Buckton, D. A. Butler, F. Thielmann, D. R. Williams Pharm Res 18 (2001) 662.
89.   F. R. Kalantzopoulou, T. Artemiacti, I. Bassiotis, N. A. Katsanos, V.  Plagianakos Chromatographia 53 (2001) 315.
90.   S. Reutenauer, F. Thielmann, J Mater Sci 38 (2003) 2205.
91.   A. H. L. Chow, H. H. Y. Tong, B. Y. Shekunov, P. York, Pharma Res 21 (2004) 1718.
92.   A. Askın A, D. T. Yazıcı ,  Chromatographia 61 (2005) 626.
93.   T. V. M. Sreekanth, K. S. Reddy, Chromatographia 65 (2007) 326.
94.   Y. C. Yang, P. R. Yoon, J. Korean, J Chem Eng 24 (2007) 451.
95.   Y.C. Yang, P. R. Yoon, J. Korean J Chem Eng 24 (2007) 165.
96.   K. Batko, A. Voelkel, J Colloid Interface Sci 315 (2007) 768.
97.   D. M. Ansari, G. J. Price, Polymer 45 (2004)3663.
98.   M. Przybyszewska, A. Krzywania, M. Zaborski, M. I. Szynkowska, J Chromatogr A 1216 (2009) 5284.
99.   J. R.  Conder, C. L. Young, In: Physical measurements by gas chromatography. Wiley, New York (1979).
100.   A.T. James, J.P. Martin, Biochem 50 (1952),
101.   J.R. Conder and C.L. young, Whiley-interscience, 1979.
102.   C. Saint Flour, E. Papirer, Ind Eng Chem Prod Res Dev 21(1982) 337.
103.   C. Saint Flour, E. Papirer, Ind Eng Chem Prod Res Dev 21 (1982) 666.
104. E.  Papirer, A. Vidal, H. Balard, Analysis of solid surface modification. In: Lloyd DR, Ward TC, Schreiber HP (eds) Inverse gas chromatography: characterization of polymers and other materials. ACS Symposium Series 391, Washington (1989) 248.
105.   T. Hamieh, M. Rageul-Lescouet, M. Nardin, H. Haı¨dara, J. Schultz, Colloids Surf A Physicochem Eng Asp 125 (1997) 155.
106.    T. Hamieh, J, Schultz, J Chim Phys 93 (1996) 1292.
107. T. Hamieh, J. Toufaily, A. H. Mouneimne, Chromatographia 73 (2011) 99.
108.  V. Gutmann,”the donor acceptor approach to molecular interactions”, Plenum Press,1978,chap:2
109. E. Brendlé and E. Papirer, Journal of colloid and interface science 194 (1997) 217.
110. J. Qiu, K. Matyjaszewski, Macromolecules 30 (1997) 5643.
111. T. E.  Patten, K.  Matyjaszewski, K.; Adv Mater 10 (1998) 901.
      

Research ptojects of Tayssir Hamieh

 

 

1. Research Project

New approach to characterize the interaction forces between microbial cells and solid surfaces: Effect of the nature of electrolyte and the geometry of solid nanoparticles

 

Key words

Microbial cells, EDL, DLVO, interaction energy, AFM, surface potential, surface charge density, asymmetrical electrolytes, Poisson-Boltzmann equation, Nonspecific Forces

 

Introduction and bibliographic review

Many works were devoted during the last twenty years to study the interaction forces between microbial cells and solid surfaces. Understanding the fundamental forces involved in the adhesion of microbial cells is of crucial importance not only in microbiology, to elucidate cellular functions, but also in medicine (biofilm infections) and biotechnology [1]. Microbial cells show remarkable adhesion properties that are of relevance to medicine and industry. The adhesion of pathogens to surfaces is the primary step leading to biofilm formation and associated infections, but cell adhesion and aggregation are also widely exploited in biotechnology for immobilizing or separating microbial cells. Cell adhesion is mediated by a multitude of molecular interactions that are specific or non-specific [2]. Abu-Lail et al. [3] combined the results of Poisson analysis with the results obtained through soft-particle Derjaguin−Landau−Verwey−Overbeek (DLVO) analysis to determine the contributions of the Lifshitz-van der Waals and electrostatic forces to the overall nonspecific interaction forces. Adhesion forces were then decoupled into specific (hydrogen bonding) and nonspecific (electrostatic and Lifshitz-van der Waals) force components using Poisson statistical analysis [3].

The nature of the physical interactions between Escherichia coli JM109 and a model surface (silicon nitride) was investigated in water via atomic force microscopy (AFM) [4]. An analysis was presented based on the application of Poisson statistics to AFM adhesion data, to decouple the specific and nonspecific interactions. The Poisson statistical analysis of adhesion forces may be very useful in applications of bacterial adhesion, because it represents an easy way to determine the magnitude of hydrogen bonding in a given system and it allows the fundamental forces to be easily broken into their components [4].

Park et al [5] studied the effect of pH conditions of growth in the specificity of interaction forces Measured Between pathogenic L. monocytogenes and silicon nitride the pH of growth media is an important factor in controlling the adherence of L. monocytogenes to inert surfaces due to the altered composition of its surface biopolymers.

A. Vilinska et al. [6] evaluated the adhesion of Leptospirillum ferrooxidans bacterial cells onto the sulfide minerals pyrite and chalcopyrite using two different physical-chemical approaches; thermodynamic and extended DLVO theory. The adhesion of microbes on interfaces and the subsequent formation of biofilms has a large influence on bioengineering processes such as environmental purification, valuable resource production, and bioremediation [7].  Yoshihara et al. [7] estimated the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface, and quantitatively evaluated the effects of the presence or absence of microbial flagella, and the microbial motility on the colloidal behaviors of microbial cells. Zhang et al. [8] studied the retention and transport of an anaerobic trichloroethene dechlorinating microbial culture in anaerobic porous media by calculating DLVO interaction energies and determining their adhesion behavior.

Many researchers were interested in understanding and controlling bacterial adhesion to material surfaces in various disciplines: biomedical, environmental and industrial. Microbial adhesion may lead to the formation of an infectious biofilm that may cause infection on biomaterials and implanted medical devices, contamination of water resources and biofouling in food-processing equipment and in many engineered and marine systems [9]. The DLVO theory has been widely used as a theoretical model not only qualitatively but also quantitatively to calculate the actual adhesion energy variations involved in bacterial (or colloidal) adhesion and aggregation as a function of separation distance between the interacting surfaces [9]. Van Oss et al. suggested an additional term called the short-range Lewis acid–base (AB) interactions to account for hydrogen bonding on close approach of bacteria and substrate surfaces, in an extended XDLVO theory [9].

 

Atomic force microscopy (AFM)

Today, AFM technique allows to determine the force strengths and length scales, ranging from weak intermolecular interactions to strong covalent bonds [1]. Currently, AFM is the only technique that is well-suited for probing forces on microbial cells, both at the single cell and single-molecule levels [1]. AFM measures the forces between a sharp probe (‘tip’) and the sample while scanning over the sample surface [1]. AFM cantilevers and tips are made of silicon or silicon nitride using microfabrication techniques. During the last years, AFM has been used increasingly to investigate microbial surfaces at high resolution. The technique provides three-dimensional images of the surface ultrastructure with molecular resolution, in real time, under physiological conditions, and with minimal sample preparation. AFM is more than a surface-imaging tool in that force measurements can be used to probe the physical properties of the specimen, such as molecular interactions, surface hydrophobicity, surface charges, and mechanical properties. These measurements provide new insight into the structure-function relationships of microbial surfaces [13].

With its ability to observe living microbial cells at nanometer resolution and to manipulate single-cell surface molecules, AFM has emerged as a powerful tool in microbiology for new structural, and functional insights into the microbial cell surface [14]. AFM-based techniques have been increasingly used for the multiparametric analysis of microbial cell surfaces, providing novel insight into their structure-function relationships. The main advantages of AFM for microbiologists are the possibility to image cellular structures at molecular resolution and under physiological conditions, the ability to monitor in situ the structural dynamics of cell walls in response to stress and to drugs, and the capability to measure the localization, adhesion, and mechanics of single cell wall constituents. Unlike other forms of microscopy, AFM operates by sensing the small forces acting between a sharp tip and the sample surface. In addition, AFM force spectroscopy can be used to quantify the forces between the tip and the sample [14].

 

Electrical double layer and Atomic force microscopy

Electrical double layer (EDL) forces develop between charged surfaces immersed in an electrolyte solution. Biological material surrounded by its physiological medium constitutes a case where these forces play a major role. Specifically, this work is focused on the study of the EDL force exerted by DNA molecules, a standard reference for the study of single biomolecules of nanometer size. The molecules deposited on plane substrates have been characterized by means of the atomic force microscope operated in the force spectroscopy imaging mode. The AFM has demonstrated its capability to provide images of biomolecules with high resolution [15]. The measurement and imaging of EDL forces arising between the AFM tip and the sample surface can be improved by combining simultaneously AFM imaging with spatially resolved force spectroscopy. This involves acquiring a force-distance curve at each pixel of a simultaneously acquired AFM topography image. Ruiz-Cabello et al. [16] showed that the colloidal-probe technique, which is based on force measurements made with the atomic force microscope, can be used to accurately determine the charging parameters of water-solid interfaces. Besides yielding accurate values of the double-layer or diffuse-layer potential, the method also allows reliable determination of the charge regulation properties of the surfaces.

In many situations, the underlying interactions involving particles and surfaces can be quantified with the DLVO theory. Double-layer forces are normally described with the Poisson-Boltzmann (PB) theory, or its linearized version, the Debye-Hückel (DH) theory. Double-layer forces depend strongly on the solution composition and the electric surface potential. Moreover, the force profiles are not determined by the potential directly at the surface, which is referred to as the surface potential, but rather by the potential at the plane of origin of the diffuse layer. This potential is called the diffuse-layer potential, double-layer potential, renormalized potential, or the effective potential. The diffuse-layer potential cannot be easily estimated even for the simplest materials, and must be measured. The advent of AFM soon led to the development of the more versatile colloidal-probe technique [16]. This method replaces the sharp AFM tip with a so-called colloidal probe, which consists of a μm-sized colloidal particle that is attached to a tip less AFM cantilever. By attaching colloidal particles to the substrate as well, one can also measure forces between two particles in the sphere-sphere geometry with the AFM.

Ruiz-Cabello et al. [16] proposed a variant of colloidal probe technique that uses a highly charged probe particle with precisely known charging properties.

 

Objectives

While the general understanding of colloidal interactions has developed significantly since the formulation of the DLVO theory, many problems still remain to be solved. One real problem is that the current theory has been developed for interactions between flat and chemically homogenous surfaces, which is in contrast to the surfaces of most natural and manufactured materials, which possess topographical variations.  Further, the geometry of nanoparticles is rather spherical or cylindrical, the presence of asymmetrical electrolytes will complicate the resolution of the Poisson-Boltzmann equation.

We propose in this research project to develop new approach to characterize the interaction forces between microbial cells and solid surfaces by studying the effect of the nature of asymmetrical electrolyte and the geometry of solid nanoparticles on these interaction forces and by combining surface thermodynamics, EDL, DLVO and AFM technique.

The modeling of these forces as well as in correlating with the findings of Abu Lail research works [4, 5, 10] with the physiochemical properties of microbes obtained using contact angle measurements and electrophoresis will be extremely useful to publish several scientific papers.

 

Methodology

First, we will be interested in the development of a new model based on the hypothesis of spherical or cylindrical particles that will be in interaction with microbial cells in presence of dissymmetrical electrolytes. This study will lead to new expressions of the surface potential and surface charge density that will allow to model the electrical double layer and the repulsive interaction energy. These theoretical results will be very useful to interpret the experimental results previously obtained.

In order to determine the interaction energies or forces between bacterial cells and solid substrates, three techniques will be used: contact angle measurements, electrophoresis and atomic force microscopy. The results obtained by Abu Lail et al. [4, 5, 10] will be taken into consideration and modeled following the obtained theoretical results.

In many previous papers [17-27], we studied the interaction energy and forces of particles in dispersion in  liquid media, the Poisson-Boltzmann equation, and more particularly the linearized model initially developed by Debye and Hückel, and applied the results on polyions like the ADN molecules, by supposing an infinite cylinder carrying a charge uniformly smeared over the surface. The stability of concentrated suspensions was also studied and the conditions of the dispersion of coal in water were optimized. The non-linear Poisson-Boltzmann equation was resolved in the case of charged spherical particles in the presence of dissymmetrical electrolytes. A more adapted and precise solution of this non-linear differential equation was given [23, 24]. By studying of the surface potential and charge density of the coal-water suspensions, we confirmed the theoretical results and we resolved an industrial problem in preparing of fluid and stable concentrated suspensions of coal in water [22, 23, 27].

We established the relationships of the electrostatic potential (x) and of the surface charge 0 and demonstrated that electrolytes of trivalent anions (1-3) and (2-3) give higher surface densities [24]. These theoretical results were confirmed by experiment in studying the surface charge and potential of the suspensions of coal in water in the presence of different dissymmetrical electrolytes [23].

Our proposed and solved model of Poisson-Boltzmann equation will allow to calculate the EDL interaction force and energy between spherical or cylindrical particles

The developed and solved Poisson-Boltzmann equation [25] is presented by the following expression:

     

Where  is the surface potential of solid particle, N Avogadro number, Zj = j the valence of ion j, e the electron charge, k the Boltzmann constant, T the absolute temperature and  the permittivity of the liquid.

With , we obtain:

 

Where                                 ,    and

Where 0 is the surface charge density.

The resolution of this differential equation when the bacterial cell is in interaction with the solid particle in presence of asymmetrical electrolytes will allow to obtain both expressions of the surface potential and the surface charge density. The advantages of this approach are following: The new model can be advantageously used for asymmetrical electrolytes and for different geometries of molecules These results will help us to determine and quantify the interaction force between cells and surfaces.

 

References

1. Sticky microbes: forces in microbial cell adhesion Yves F. Dufrêne, Trends in Microbiology, 2015, 23, No. 6, 376-382.
2. Müller, D.J. et al. Force probing surfaces of living cells to molecular resolution. Nat. Chem. Biol. 2009, 5, 383–390
3. F. Pinar Gordesli and Nehal I. Abu-Lail, Combined Poisson and Soft-Particle DLVO Analysis of the Specific and Nonspecific Adhesion Forces Measured between L.monocytogenes Grown at Various Temperatures and Silicon Nitride, Environ Sci Technol. 2012, 46(18):10089-98.
4. Nehal I. Abu-Lail and Terri A. Camesano, Specific and Nonspecific Interaction Forces Between Escherichia coli and Silicon Nitride, Determined by Poisson Statistical Analysis, Langmuir 2006, 22, 7296-7301
5. Bong-Jae Park, Fatma Pinar Gordesli, and Nehal I. Abu-Lail, The Role of pH Conditions of Growth in the Specificity of Interaction Forces Measured Between Pathogenic L. monocytogenes and Silicon Nitride, J. Bionanosci. 2014, 8, 1-12
6. A. Vilinska and K. Hanumantha Rao, Surface thermodynamics and extended DLVO theory of Leptospirillum ferrooxidans cells' adhesion on sulfide minerals, Minerals & Metallurgical Processing, 2011, 28, No. 3, pp. 151-158
7. Yoshihara A, Nobuhira N, Narahara H, Toyoda S, Tokumoto H, Konishi Y, Nomura T., Estimation of the adhesive force distribution for the flagellar adhesion of Escherichia coli on a glass surface, Colloids and Surfaces B: Biointerfaces, 2015, 131 67–72
8. Huixin Zhang, Ania C. Ulrich, Yang Liu, Retention and transport of an anaerobic trichloroethene dechlorinating microbial culture in anaerobic porous media, Colloids and Surfaces B: Biointerfaces, 2015, 130, 110–118
9. Sonia Bayoudh, Ali Othmane, Laurence Mora, Hafedh Ben Ouada, Assessing bacterial adhesion using DLVO and XDLVO theories and the jet impingement technique, Colloids and Surfaces B: Biointerfaces, 2009 73, 1–9
10. Bong-Jae Park, Nehal I. Abu-Lail, The role of the pH conditions of growth on the bioadhesion of individual and lawns of pathogenic Listeria monocytogenes cells, Journal of Colloid and Interface Science, 2011, 358, 611–620
11. Fatma Pinar Gordesli, Nehal I. Abu-Lail, Impact of ionic strength of growth on the physiochemical properties, structure, and adhesion of Listeria monocytogenes polyelectrolyte brushes to a silicon nitride surface in water, Journal of Colloid and Interface Science, 2012, 388, 257–267
12. F. Alejandro Bonilla, Natalie Kleinfelter, John H. Cushman, Microfluidic aspects of adhesive microbial dynamics: A numerical exploration of flow-cell geometry, Brownian dynamics, and sticky boundaries, Advances in Water Resources, 2007, 30, 1680–1695
13. Yves F. Dufrêne, Atomic Force Microscopy, a Powerful Tool in Microbiology, J. Bacteriology, Oct. 2002, p. 5205–5213 Vol. 184, No. 19
14. Dufrêne YF. 2014. Atomic force microscopy in microbiology: new structural and functional insights into the microbial cell surface. MBio. 2014 Jul 22;5 (4) e01363-14.
15. J. Sotres and A. M. Baro, AFM Imaging and Analysis of Electrostatic Double Layer Forces on Single DNA Molecules, Biophysical Journal, Volume 2010, 98, 1995–2004
16. F. Javier Montes Ruiz-Cabello, Gregor Trefalt, Plinio Maroni, and Michal Borkovec, Electric double-layer potentials and surface regulation properties measured by colloidal-probe atomic force microscopy, Physical Review E, 2014, 90, 012301
17. T.  Hamieh, J. Toufaily and H. Alloul, Physicochemical Properties of the Dispersion of Titanium Dioxide in Organic Media by Using Zetametry Technique, J. Dispersion Science Technology, JDST, 2008, 29 (9), 1181-1188.
18. T. Hamieh, M. Rageul-Lesouet, M. Nardin, M. Rezzaki et J. Schultz, Study of specific interactions between some metallic organic model molecules, J. Chim. Phys., 1997, 94, 503-524. .
19. T. Hamieh, M. Rageul-Lesouet, M. Nardin, H. Haidara et J. Schultz, Study of acid-base interactions between some metallic oxides and model organic molecules, Colloids and Surfaces A,
20. T. Hamieh, Surface charge density and potential of coal liquid mixtures and controls of their stability and fluidity, J. Mat. Sci., 1996, 31, 5665-5669.
21. T. Hamieh, M. Rageul-Lesouet, M. Nardin et J. Schultz, Etude des propriétés superficielles de quelques oxydes métalliques par chromatographie gazeuse inverse et par zétamétrie en milieux aqueux et organique, J. Chim. Phys., 1996, 93, 1332-1363.
22. T. Hamieh and B. Siffert, Theoretical and practical study of a stability test: application to highly concentrated coal suspensions, Advanced Powder Technol., 1994, 5(2), 143-160.
23. T. Hamieh and B. Siffert,  Theoretical and Experimental Study of the Surface Charge Density and Surface Potential of Coal-Water Suspensions in Dissymmetrical Electrolytes, Colloids and Surfaces, 1994, 84, 217- 228.
24. T. Hamieh and B. Siffert, Calcul du potentiel et de la densité de charge de surface d’une sphère chargée en présence d’électrolytes dissymétriques, J. Chim. Phys., 1992, 89, 1799-1834.
25. T. Hamieh and B. Siffert, Interactions between particles in suspension: application to coal-water suspensions, J. Chim. Phys., 1991, 88, 537-542.
26. T. Hamieh and B. Siffert, Determination of point of zero charge and acid-base superficial coal groups in water, Colloïds and Surfaces, 1991, 61, 83-96.
27. B. Siffert and T. Hamieh, Effect of mineral impurities on the charge and surface potential of coal: application to obtaining concentrated suspensions of coal in water, Colloids and Surfaces, 1989, 35, 27-40.

 

 

1. Research Project

Characterization of superficial physicochemical properties of materials by inverse gas chromatography (IGC) at infinite dilution

 

IGC at infinite dilution is a powerful technique widely used to study surface properties of adsorbents, oxides, cellulose starches or other polymers and polymers adsorbed on metals or oxides.

In many previous studies [1-3], we used inverse gas chromatography (IGC) to characterise the surface characteristics of various oxides and polymers, especially, their surface energies and their interactions with some organic molecules. In this paper, we used IGC technique at infinite dilution [4] on some oxides like, Monogal, MgO, ZnO, SiO2 and Al2O3 carbon fibres, PMMA/alumina and PMMA/silica systems that are known to interact strongly through acid-base interactions and ionic bonds [5].

On the other hand, it is obvious that the polymer properties extremely depend on the temperature. Polymers can be easily affected by abrupt variations of the temperature. In fact, such modifications would induce modifications in the chain segment mobility of polymers. These changes in mobility arising at the glass transition temperatures (Tg) of bulk polymers can be determined advantageously by using IGC technique [6-12]. Some of these polymers can be used in food science for packaging and/ or protection. The interactions between some food and packaging can be also studied by IGC at infinite dilution.

The interest for IGC in food science is increasing in particular when a humidity control is available. For example, the chewing gum polymers give the opportunity to transfer IGC methodology into food science. Gas–liquid chromatography (GLC) was used for the determination of solubility parameters of synthetic polymers such as poly(dimethylsiloxane) and poly(methylmethacrylate) [13]. Price and Guillet and co-workers [3, 9–13] were the pioneers in the physico-chemical interpretation of GLC data from polymers. Pawlisch [24] [14], Macris [15] and Danner and co-workers [16,17] used GLC for purposes going from thermodynamic parameters to diffusion coefficient by capillary IGC. In food science, King and List [18] used GLC to study the interactions of several volatile compounds in soybean oil. Boutboul [19], Delarue and Giampaoli [20], and Boutboul et al. [21] were able to characterise the type of interactions (London,Van der Waal’s dipole–dipole or H-bonding) between starch and several flavour molecules. Gauthier et al [22] showed that attractive or repulsive forces could be calculated from IGC data. Bencze´di and Tomka [23– 25] calculated thermodynamic parameters characterizing water–starch interactions by IGC and developed an equation calculating the solubility parameter of starch using only water as solvent and described the physico-chemical characterization of two different chewing gum bases and the interactions with the incorporated flavour molecules using inverse gas chromatography as a specific technique [26-36].

 

Boutboul et al. [37] studied the interactions between aroma compounds and native corn starch were studied by inverse gas chromatography (IGC). A system of humidification of the carrier gas has been set up and generated a fixed and stable relative humidity of 56.3%. The IGC system worked under pressure (2.1 bars), using starch as stationary phase without any support. This technique allowed to maintain the starch matrix with a constant water content of 10%. The specific retention volumes of volatiles (1-hexanol, 2-hexanol, octanal, ethyl hexanoate and d-limonene) were measured under dry and humid conditions. Retention was higher under humid conditions, especially for 1-hexanol. Retention indices of volatiles with various functions and carbon chain lengths were determined on starch and compared to RI on Carbowax. RI on starch increased with the carbon chain length, like on Carbowax. Retention on starch and Carbowax followed the same general order, relative to the functional group.

It is known that interactions between aroma compounds and food components play an important role in the perception of flavour. Knowledge of these interactions is useful in improving the process and the flavouring of food products [38]. Carbohydrates, particularly starch, are present in many low-water content foods, like cereal-based products. They are also widely used as solid support for aroma compounds [39], and as fatreplacers [40].

Buckton and Gill [41] studied the importance of surface energetics of powders for drug delivery and the establishment of inverse gas chromatography. Powders used here are complex systems with more than one value for surface energy. The presence of different faces, defects, physical forms and impurities will alter the surface properties. There are few good ways to measure powder surface energies, with vapour sorption, especially inverse gas chromatography (IGC) being a logical choice. The significance of surface energy is reviewed briefly, as is the difference between contact angle and IGC data. The utility of IGC for studies of batch to batch variability and some issues relating to finding a suitable number to describe a complex range of surface energies are discussed. The utility of IGC in studies of the amorphous state is shown, where there is value in being able to monitor molecular mobility thresholds, glass transition, collapse and crystallization, as well as relaxation and its impact on surface energy. The conclusion is that the complexity of powders means that scientists should not expect simple correlations between measurements and performance, but that correlations are likely to be there if the correct data are recorded in the most appropriate way [41, 42].

 

Also the study of surface properties of powders used in food or in pharmaceutical industries can be expected to provide data that will at worst explain batch to batch variability, and at best provide control for approaches such as inverse gas chromatography, because it is logical that surface science of powders will be a factor to consider and thus vital to understand how surface properties may best be measured for powders used in food or in pharmaceutical industries. Inverse gas chromatography (IGC) is becoming well known in the pharmaceutical sector, although publications have only started in this field in the early 1990s [43], the technique was already well established in other disciplines and the subject of a number of books [44–48].

 

Gamelas et al. [49] recently studied the surface properties of distinct nanofibrillated celluloses by inverse gas chromatography. The adhesion and surface properties of nanocelluloses are an important issue to consider when using this material for composites production, in food packaging or coatings, as well as for determining the influence of added functional groups. In their recent paper Gamelas et al. [49] studied the surface properties of two nanofibrillated celluloses obtained by mild 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation with distinct mechanical treatment intensity in a homogenizer (5 and 15 passes), and one nanofibrillated cellulose obtained by enzymatic process, using the inverse gas chromatography at infinite dilution. The dispersion component of the surface energy gsd was 42–46 mJ m−2 at 40◦C for the TEMPO nanofibers and 52 mJ m−2 for the enzymatic nanocellulose. It was confirmed, based on the determination of the specific components of the works of adhesion and enthalpies of adsorption with polar probes, that the surfaces of the materials have a more Lewis acidic than Lewis basic character [50].

It is well-known that the surface properties of solid materials and the dispersive component of the surface energy can be determined by inverse gas chromatography technique that can also allow to obtain the adsorption thermodynamic parameters as specific components of the free energy, enthalpy and entropy of adsorption, Lewis acid–base character of the surface, surface nanoroughness parameter, etc. [51-54]. Thus, using IGC, a cellulosic fibrous material can be thoroughly characterized with respect to its surface chemical properties. Besides, this technique is advantageous over the classical contact angle measurements for the analysis of porous, rough, heterogeneous and hydrophilic surfaces. Some recent papers reported the use of IGC to analyze nanocellulose [55–59]. In particular, under infinite dilution conditions, the dispersion component of the surface energy was determined for cellulose nanofibers obtained by enzymatic pre-treatments [55] and cellulose nanofibers extracted from hemp fiber by acid hydrolysis and mechanical treatment [56]. For the latter, the Lewis acid–base characteristics were also assessed. The influence of the drying method on the surface energy of cellulose nanofibrils was also evaluated [58]. Gamelas et al. [49] used two nanofibrillated celluloses obtained from an eucalypt bleached kraft pulp by NaClO/TEMPO/NaBr pre-oxidation with distinct mechanical treatment intensity, and one nanofibrillated cellulose obtained by enzymatic process, were thoroughly analyzed for their surface properties by inverse chromatography.

In food sciences, polymers have become one of the main alternatives as materials for the manufacture of food packages; their wide versatility makes feasible the design of suitable containers to fulfil the requirements of every food stuff [59]. However, most of these packages are very difficult to recycle or re-use, generating huge volumes of residues. For this and other reasons, food packaging industry is starting to substitute the traditional polymeric materials for biodegradable ones. The number of biodegradable polymers tested in laboratories is huge, although only a few of them are already used in commercial food packaging applications. The poly(lactic acid)(PLA) and the polycaprolactone (PCL) are among this selected group. Nowadays, the PLA is already commercially used as a substitute of PET in the design of rigid (or semi-rigid) containers. PCL, generally used as additive to ease the process ability of other polymers, is also starting to be used by itself in some applications competing with polyolefins. The PLA is an aliphatic polyester usually synthesized via polymerization of lactic acid, which is mainly derived from corn or whey [60]. Due to its ability to be degraded and assimilated inside the human body within a few months, its first applications were in the biomedical field [61–64]. Recently, due to a decrease on its costs of production, its introduction in the food packaging industry has become possible. In contact with water, it slowly degrades by hydrolysis, delimiting its application to short self-life containers as drinking cups, salad containers and blisters [65]. On the other hand, the oil-derived PCL cannot be degraded by water, but bacteria only need a few weeks to compost it [66]. This semi-crystalline polyester, manufactured by ring-opening polymerization of ε-caprolactone, is characterized by its low melting and glass transition temperatures, as well as by its high elongation at break, low modulus and chain flexibility [67]. The latter properties make it suitable for the production of non-rigid containers or bags.

During the last years, lots of research have been addressed to the improvement of the properties of polymeric materials by loading them with small amounts of dispersed or exfoliated clays, obtaining micro- or nanocomposites. Just by adding the clay particles to the polymeric matrix, properties like its fire ignition resistance are improved, but the dispersion of the particles and its adhesion to the polymer are also needed to improve the mechanical properties and the gas barrier performance of the resulting materials [67–70]. However, the latter situation is not usually obtained in a spontaneous way, and both surfaces need to be modified in order to increase its compatibility and miscibility. Similar comments are valid for the development of composites with biodegradable fibers. In these materials, natural fibers and nanofibers from diverse plant origins are used, instead of synthetic fibers, to reinforce polymeric materials. Besides the development and improvement of polymeric materials, many other properties of plastic packages depend upon adequate surface characteristics, such as printability, surface adhesion in lamination and coextrusion of structures, compatibility with the packed product, especially with foodstuff, and adhesion of microorganisms to food package surfaces. One technique able to characterize the surface of both, polymers and clays, and therefore suggest which surface modifications are required to obtain this outstanding materials is inverse gas chromatography (IGC) [71,72].

Inverse gas chromatography (IGC) is capable to characterize the surface properties (surface energy, heat of adsorption, and specific interaction of adsorption) of materials [73] and recently pharmaceuticals [74-77]. IGC is a real source of physiochemical data [78]. It can be applied to observe the interaction between polymers and organic solvent systems under the conditions approaching infinite dilution of the volatile component [79]. It can be also used to determine the glass transition temperature (Tg) of polymers or amorphous pharmaceuticals and to study the plasticizing effect of water on these materials [80]. This technique is adequate to determine the Lewis acid-base properties of thermoplastic and thermosetting polymer insulating materials [81] or to analyze the area of cellulosic multipurpose office paper [82]. Many other studies were devoted to conducting polymers by Al Saigh and al. [83, 84], and Boukerma and al. [85] and Bailey and al. [86]. ICG is also used to determine the solubility parameters of some solid surfaces as titanate modified silica gel [87] or to compare the surface energies of crystalline, amorphous, and ball milled lactose [88], also to determine the heterogeneous surfaces [89] and textile their products and physicochemical properties [90] ,and to determine  surface energy and surface area of powdered materials [91,92].

The ICG technique is able to analyze the solvent-solvent interactions [93], the surface properties of clays [94, 95], nanomaterials and clay-polymer composites [96, 97], nanoparticles with respect to their specific surface area, particle size and morphology [98], pharmaceutical and food products.

 

In this project, we are interested in the determination of superficial physiochemical properties of some materials, more particularly the determination of surface energy, specific free enthalpy of adsorption of organic molecules and solid substrates, the specific enthalpy and entropy of interactions, the acid-base constants in Lewis terms. We will study also the effect of humidity of the medium on the interaction properties of food packaging.

 

We give below some details on the inverse gas chromatography technique (IGC):

 

Methods of IGC

For over 30 years, inverse gas chromatography has been used to determine the superficial phenomena, glass transitions and acid-base properties of solid materials [99]. We applied this technology to determine the changes, as a function of temperature, of the superficial properties of some polymers and polymers adsorbed on oxides. Probes of known properties are injected into the column containing the solid. The retention times of these probes, measured at infinite dilution, allow us to determine the interactions between model organic molecules and the solid, if we assume there is no interaction between the probe molecules themselves. Measurements were carried out with a DELSI GC 121 FB chromatograph equipped with a flame ionization detector of high sensitivity. The data retention was obtained with a stainless steel column 15-30 cm long and 2 mm internal diameter packed with 1-2 g of solids in powder or fibre forms.

 

Retention volume

The net retention volume Vn which serves to determine the thermodynamic quantities, it is the volume of carrier gas through the column since the introduction of the probe until the output of the maximum of the peak of the inferred methane retention volume V0. It is influenced by the retention time according to the following relation:

Vn = Dc (tr – t0)                                                                  (1)

With Dc representing the corrected of the carrier gas given by the following equation (2). The flow rate correction is given by:

   Dc = j Dm (1+  )                                                       (2)

 

Dm is the measured flow rate of the carrier gas with the bubble flow meter at the outlet of the column. Tc and Ta are respectively the column temperature and the ambient temperature at the time of flow measurement, Patm et PH2O are respectively the atmosphere pressure at the time of analysis and the saturation vapour pressure of water at Ta.

The coefficient j for James Martin [100] takes account of the compressibility of the gas in the column under the action of the charge loss ΔP in the column:

                                                  3 (1 +) 2 -1

 J =                                                                                                              (3)                                                                                                                                                               

                                                    2 (1+) 3-1

 

This coefficient is always less than or equal to 1 [101].

The specific retention volume Vg is also used; it can report the net retention volume to the unit mass of adsorbent and to the temperature 0˚C:

 

  Vg =                                                                        (4)

 

Method of Papirer et al.

Many methods were used to determine the specific interactions exchanged between polar molecules and a solid surface and then obtain the acid- base interactions [73-77, 102-107].

Papirer and al. developed the method giving the more precise specific free enthalpy of interaction between a probe and a solid [102-104]. When plotting RTlnVn against lnP0, Papirer et al have obtained a straight line, where P0 is the vapour pressure of the probes. For a homologous series of n-alkanes (from n-pentane C5 to n-decane C10), Papirer and al. wrote the following equation:

RT ln Vn =A ln P0 ‏ + B                                       (5)

Where A and B are constant depending on the nature of the solid substrate. If polar probes (as for example Toluene) are injected into the column, specific interactions are made between these probes and the solid surface and G0 is now given by:

                                      ΔGo = ΔGd   + ΔGSP                                                             (6)

We can deduce the various values of the free specific enthalpy ΔGSP of the polar molecules at different temperatures, by using Papirer and al. approach.

Then by plotting ΔGSP of the polar molecules as a function of the temperature from the equation:               

ΔGSP = ΔHSP -T ΔSSP                                             (7)

We can deduce the specific enthalpy (ΔHSP) and entropy (ΔSSP) of interaction between the copolymer and the polar molecules.

Determining ΔGaSP at different temperatures is used to draw the straight line of variation of ΔGaSP in function of T. The slope of this line is equal to ΔSaSP and intercepts to ΔHaSP.

 

The method of Guttmann

Inverse gas chromatography is used to evaluate Lewis type acid- base interactions, exchanged between a solid surface and polar molecules. Guttmann [108] classified the polar molecules by assigning an electron donor (ND) and a number of electron acceptor (NA) which realizes respectively the acidity and the basicity of the molecule. In analogy to the approach of Guttmann, Papirer and al [109]   proposed to characterize the solid by two parameters KA and KD respectively reflect the basic and the acidic character of the solid. These two constant measure the ability of the solid to develop respectively the acid and base interactions with basic, acidic or amphoteric probes. They are connected to the specific enthalpy ΔHaSP through the following equation:

- ΔHaSP = KA.ND + KD.NA                                           (8)

Where KA and KD respectively represent the acidic and the basic character of the solid and NA and ND represent the donor number and the electron acceptor of the probe according to the scale of Guttmann [108].

Equation 8 can be written as:

                          KA+ KD                                             (9) 

 

The representation of  in function of   gives in general a straight line of slope KA and intercept KD.

 

 

Description of the chromatography in gas phase apparatus.

The chromatography apparatus is composed of several parts:

 

a-injector: this is the part where the mixture of analytes were injected and evaporated . to facilitate its passage from the injector to the column (also called kiln),the inlet temperature must be higher than that of the furnace. The injection is done by using a micro syringe.

 

b-the column: it is formed from a solid support and a tube of stainless steel, glass or Teflon (for the analysis of corrosive products). When it passes from the injector to the column, the mixture of the analyte migrates there through with a carrier gas (inert gas in the column) and the individual products are separated according to their molecular weight (the lighter get out of the column first) or to their polarity (if the column is polar ,it will retain the polar product longer than the apolar or weakly polar product and the latter (non polar product and weakly polar ) get out first from the column .if the column is apolar the reverse will happen.

 

c-the detector: at the outlet of the column the products pass into a detector where they are analyzed. Since separated, each product gives a signal in the form of a peak (Gauss). The surface of this peak is proportional to the mass or volume concentration of the product in the mixture.

 

 

New model (Hamieh et al. model) [107]

IGC allows to give the retention volumes obtained from different probes (n-alcanes and polar). These volumes allow the determination of RTlnVn values of different polar probes (figure 5) as well the determination of the values of their specific interactions ΔGSP representing the difference between the value of RTlnVn and the corresponding point to its projection on the axis of RTlnVn=f(log Po).

Once ΔGSP is determined for different temperatures it is possible to trace its variation in function of the temperature. A straight line can be obtained and whose slope gives the value of ΔHSP and by the intercept we get -ΔSSP.

The obtained value of ΔHSP is used to determine the values of KA and KD (in our case this equation is treated using the classical model and the model of Hamieh [106, 107]   it is recalled here that the classical model is given by :

- ΔHSP = KA.ND+KD.NA                                            (11)

With NA and ND the electron acceptor and donor numbers, respectively.

While Hamieh’s model [107] corrected the relationship (11) and proposed a new relationship by adding a third parameter K reflecting the amphoteric character of the oxide or polymer according to:

 (- Hsp) = KA DN + KD AN – K DN AN                                            (12)

By dividing by AN, we obtain:

                                           (13)

Equation (13) can be symbolically written as:

X1 = KD + KA X2 - K X3                                               (14)

Where                     ,,  and K = K(KA,KD)

X1, X2 and X3 are known for every polar molecule, whereas KD, KA and K are the unknown of the problem.

     By using N probes, relationship (14) will allow us to write the following equations:

                                  (15)

             (16)

             (17)

One obtains a linear system given by the equations (15-17) at three unknown numbers: KD, KA and K. The matrix representing this linear application is a symmetrical one; we deduce that the problem (15-17) has a unique solution for N ³ 3. We can apply this method to calculate the acid-base constants of our solid substrates. 

 

Determination of the surface energy of solids

The dispersive component of the surface energy of solids  gsd was determined by using the well-known relationship of Fowkes expressing the geometric mean of the dispersive components (exponent d) of the surface energy of the probe gld and the solid  gsd  :

DGo = DGd   = NaWa = 2Na(gld gsd) 1/2                              (18)

where Wa is the energy of adhesion, N is Avogadro’s number and a the surface area of one adsorbed molecule of the probe .

By plotting RTlnVn as a function of 2Naof n-alkanes, we can deduce, from the slope of the straight line, the value of dispersive component of the surface energy of the solid. 

 

References

 

1. Hamieh T, Rageul-Lescouet M,  Nardin M et Schultz J (1996), J. Chim. Phys. 93,  1332-1363.
2. Hamieh T, Rageul-Lescouet M,  Nardin M, Haïdara H, Schultz J (1997), Colloids and Surfaces A: Physicochemical and Engineering Aspects, 125, 155-161.
3. Hamieh T, Rezzaki M,  Grohens Y and Schultz J (1998), J. Chim. Phys. 95,  1964-1990.
4. Conder JR, Young CL (1979), Physical measurements by gas chromatography. J. Wiley and  Sons, New York.
5. Van Alsten J.G, Sauer B.B., Walsh J, (1992), Macromolecules, 25, 4046-4048.
6. Saint Flour C, Papirer E (1982), Ind. Eng. Chem. Prod. Res. Dev.  21, 2, 337-341.
7. Saint Flour C, Papirer E (1982), Ind. Eng. Chem. Prod. Res. Dev.  21, 4, 666-669.
8. Papirer E, Vidal A and Balard H (1989), Analysis of solid surface modification. P. 248-261 in  Inverse Gas Chromatography: Characterization of Polymers and Other Materials, ACS Symposium Series 391, Lloyd D.R., Ward T.C. and Schreiber ed., Washington.
9. Gutmann V (1978), The Donnor-Acceptor Approch to Molecular Interaction. Plenum Press, New York.
10. Siffert B, Kuczinski J and Papirer E (1990), J. Colloid. Interface Sci. 135, 1, 107-117.
11. Fowkes FM  (1964), Ind. Eng. Chem. 56, 12, 40-52.
12. Schultz J, Lavielle L, Martin C (1987),  J. Chim. Phys. 87, 2, 231.
13. G .J. Price, J.E. Guillet, J. Solut. Chem. 6 (1986) 605.
14. K .B. de Roos, Flavour Sci. Technol. (2002) 355
15. W .W. Lee, Pharm. Technol. On-Line (2001) 1. 16.
16. J . Bronislaw, Patent WO 99/44436, 1999.
17. P . Schmiedel, M. Jekel, Patent EP01/08279(C03K), 2002.
18. A .J. Ashworth, G.J. Price, Macromolecules 19 (1986) 358.
19. G .J. Price, J.E. Guillet, J. Solut. Chem. 16 (1987) 605.
20.   G . DiPaola-Baranyi, J.E. Guillet, Macromolecules 11 (1978) 228.
21.   J .E. Lipson, J.E. Guillet, in: R.B. Seymour, G.A. Stahl (Eds.), Macromolecular Solutions. Solvent–Property Relationships in Polymers, Pergamon Press, New York, 1980.
22.   D .G. Gray, J.E. Guillet, Macromolecules 7 (1974) 244.
23.   J .M. Braun, J.E. Guillet, Adv. Polym. Sci. 27 (1976) 107.
24.  C .A. Pawlish, PhD thesis, University of Massachusetts, Amherst, MA, 1985.
25.   A . Macris, MS thesis, University of Massachusetts, Amherst, 1979.
26.   I . Hadj Romdhane, R.P. Danner, AIChE J. 39 (1993) 625.
27.   I . Hadj Romdhane, R.P. Danner, J.L. Duda, Ind. Eng. Chem. Res. 34 (1995) 2536.
28.   J .W. King, G.R. List, J. Am. Oil Chem. Soc. 67 (1990) 1.
29.   A . Boutboul, Dissertation, Paris XI Orsay, 2001.
30.   J . Delarue, P. Giampaoli, J. Agric. Food Chem. 48 (2000) 2372.
31.   A . Boutboul, P. Giampaoli, A. Feigenbaum,V. Ducruet, Food Chem. 71 (2000) 387.
32.   H . Gauthier, A.-C. Coupas, P. Villemagne, R. Gauthier, J. Appl. Polym. Sci. 69 (1998) 2195.
33.   D . Benczédi, I. Tomka, F. Escher, Macromolecules 31 (1998) 3055.
34.   D . Benczédi, I. Tomka, F. Escher, Macromolecules 31 (1998) 3062.
35.   D . Benczédi, Trends Food Sci. Technol. 9 (1999) 1.
36.  Brigitte Niederer, Anh Le, Ennio Cantergiani,, Journal of Chromatography A, 996 (2003) 189–194
37. Boutboul, P. Giampaoli , A. Feigenbaum , V. Ducruet, Food Chemistry 71 (2000) 387-392
38. Dubois, C., Lubbers, S., & Voilley, A. (1995). Industries Alimentaires et Agricoles, 112, 186-193.
39. Goubet, I., Le Quere, J. L., & Voilley, A. J. (1998). Journal of Agricultural and Food Chemistry, 46, 1981-1990
40. Godshall, M. A. (1997). Food Technology, 51(1), 63-67
41. Graham Buckton, Hardyal Gill, Advanced Drug Delivery Reviews 59 (2007) 1474–1479
42. M. Rillosi, G. Buckton, Pharm. Res. 12 (1995) 669–675.
43. [11] Djordjevic, G. Rohr, M. Hinterleitner, B. Schreiber Int. J. Pharm. 81 (1992) 21–29.
44. [12] J.R. Conder, C.L. Young, Physicochemical Measurement by Gas Chromatography, Wiley-Imterscience, Chichester, 1979.
45. [13] R.J. Laub, R.L. Pecsok, Physicochemical Applications of Gas Chromatography, Wiley_interscience, New York, 1978.
46. [14] D.R. Lloyd (Ed.), Inverse Gas Chromatography, American Chemical Society, Washington DC, 1989.
47. [15] O. Planinsek, G. Buckton, Inverse gas chromatography: considerations about appropriate use for amorphous and crystalline powders, J. Pharm. Sci. 92 (2003) 286–1294.
48. [16] V. Gutmann, The Donor-acceptor Approach to Molecular Interactions, Plenum, New York, 1978.
49. José A.F. Gamelas∗, Jorge Pedrosa, Ana F. Lourenc¸ o, Paulo J. Ferreira, Colloids and Surfaces A: Physicochem. Eng. Aspects 469 (2015) 36–41
50. H. Kangas, P. Lahtinen, A. Sneck, A-M. Saariaho, O. Laitinen, E. Hellén, Nord. Pulp Paper Res. J. 29 (2014) 129–143.
51. J.M.R.C.A. Santos, J.T. Guthrie, Mater. Sci. Eng. R50 (2005) 79–107.
52. J.A.F. Gamelas, Cellulose 20 (2013)2675–2693.
53. P. Mukhopadhyay, H.P. Schreiber, Colloids Surf. A 100 (1995) 47–71.
54. J.A.F. Gamelas, E. Ferraz, F. Rocha, Colloids Surf. A 455 (2014) 49–57.
55. N. Siddiqui, R.H. Mills, D.J. Gardner, D. Bousfield, J. Adhes. Sci. Technol. 25 (2011)709–721.
56. B. Wang, M. Sain, Bioresources 2 (2007) 371–388.
57. M. Pommet, J. Juntaro, J.Y.Y. Heng, A. Mantalaris, A.F. Lee, K. Wilson, G.Kalinka, M.S.P. Shaffer, A. Bismarck, Biomacromolecules 9 (2008) 1643–1651.
58. Y. Peng, D.J. Gardner, Y. Han, Z. Cai, M.A. Tshabalala, J. Colloid Interface Sci. 405 (2013) 85–95.
59. D. Cava, R. Gavara, J.M. Lagaréon, A. Voelkel, Journal of Chromatography A, 1148 (2007) 86–91
60. V.K. Holm, S. Ndoni, J. Risbo, J. Food Sci., 71 (2006), p. E40
61. C.G. Pitt, M.M. Gratzl, G.L. Kimmel, J. Surles, A. Schindler, Biomaterials, 2 (1981), p. 215
62. P. Mainil-Varlet, R. Curtis, S. Gogolewski, J. Biomed. Mater. Res., 36 (1997), p. 360
63. N.C. Bleach, K.E. Tanner, M. Kellomaki, P. Tormala, J. Mater. Sci.: Mater. Med., 12 (2001), p. 911
64. H. Tsuji, K. Sumida, J. Appl. Polym. Sci., 79 (2001), p. 1582
65. R. Auras, B. Harte, S. Selke, J. Appl. Polym. Sci., 92 (2004), p. 1790
66. C.D. Kesel, C.V. Wauven, C. David, Polym. Degrad. Stab., 55 (1997), p. 107
67. S. Sinha Ray, M. Bousmina, Prog. Mater. Sci., 50 (2005), p. 962
68. M. Alexandre, P. Dobuis, Mater. Sci. Eng., 28 (2000), p. 1
69. G. Gorrasi, M. Tortora, V. Vittoria, D. Kaempfer, R. Mülhaupt, Polymer, 44 (2003), p. 3679
70. J.C. Grunlan, A. Grigorian, C.B. Hamilton, A.R. Mehrabi, J. Appl. Polym. Sci., 93 (2004), p. 1102
71. D.M. Ansari, G.J. Price, Polymer, 45 (2004), p. 1823
72. E. Fekete, J. Móczo, B. Pukánszky, J. Colloid Interface Sci., 269 (2004), p. 143
73. HP. Schreiber DR.  Lloyd, American Chemical Society, Washington (1989) 1.
74.    D. Cline, R. Dalby, Pharm Res 19 (2002) 1274.
75.     J. C. Feeley, P. York, B. S. Sumby, H. Dicks, Int J Pharm 172 (1998) 89.
76.    M. D. Ticehurst Ph.D. thesis, University of Bradford, York (1995).
77.    G. Buckton, Adv Drug Delivery Rev 26 (1997) 17.
78.   A. Voelkel, B. Strzemiecka, K. Adamska, K. Milczewska, J. Chromatogr A 1216 (2009) 1551.
79.   M. Tazaki, R. Wada, M. Okabe, T. Homma,  Polym Bull 44 (2000) 93.
80.   R. Surana, L. Randall, A. Pyne, N. M. Vemuri, R. Suryanarayanan, Pharm Res 20 (2003) 1647.
81.   S. Baoli, Z. Qianru, J. Lina, L. Yang, L, Bin, J Chromatogr A 1149 (2007) 390.
82.   J. Santos, H. Gil, A. Portugal, J. T. Guthrie, Cellulose 8 (2001) 217.
83.   A. Al-Ghamdi Z. Y. Al-Saigh, J Chromatogr A 969 (2002) 229.
84.   R. Wu, D.  Que, Z. Y. Al-Saigh, J Chromatogr A 1146 (2007) 93.
85.   K. Boukerma, M.  Micˇusˇı´k, M. Mravcˇa´kova´, M. Omastova´, M. J. Vaulay, P. Beaunier, N. M. Chehimi, Colloids Surf A 293 (2007) 28.
86.   R. A. Bailey, K. C. Persaud, Anal Chim Acta 363 (1998) 147.
87.   A. Voelkel, T. Grzeskowiak, Chromatographia 51(2000) 608.
88.   H. E. Newell, G. Buckton, D. A. Butler, F. Thielmann, D. R. Williams Pharm Res 18 (2001) 662.
89.   F. R. Kalantzopoulou, T. Artemiacti, I. Bassiotis, N. A. Katsanos, V.  Plagianakos Chromatographia 53 (2001) 315.
90.   S. Reutenauer, F. Thielmann, J Mater Sci 38 (2003) 2205.
91.   A. H. L. Chow, H. H. Y. Tong, B. Y. Shekunov, P. York, Pharma Res 21 (2004) 1718.
92.   A. Askın A, D. T. Yazıcı ,  Chromatographia 61 (2005) 626.
93.   T. V. M. Sreekanth, K. S. Reddy, Chromatographia 65 (2007) 326.
94.   Y. C. Yang, P. R. Yoon, J. Korean, J Chem Eng 24 (2007) 451.
95.   Y.C. Yang, P. R. Yoon, J. Korean J Chem Eng 24 (2007) 165.
96.   K. Batko, A. Voelkel, J Colloid Interface Sci 315 (2007) 768.
97.   D. M. Ansari, G. J. Price, Polymer 45 (2004)3663.
98.   M. Przybyszewska, A. Krzywania, M. Zaborski, M. I. Szynkowska, J Chromatogr A 1216 (2009) 5284.
99.   J. R.  Conder, C. L. Young, In: Physical measurements by gas chromatography. Wiley, New York (1979).
100.   A.T. James, J.P. Martin, Biochem 50 (1952),
101.   J.R. Conder and C.L. young, Whiley-interscience, 1979.
102.   C. Saint Flour, E. Papirer, Ind Eng Chem Prod Res Dev 21(1982) 337.
103.   C. Saint Flour, E. Papirer, Ind Eng Chem Prod Res Dev 21 (1982) 666.
104. E.  Papirer, A. Vidal, H. Balard, Analysis of solid surface modification. In: Lloyd DR, Ward TC, Schreiber HP (eds) Inverse gas chromatography: characterization of polymers and other materials. ACS Symposium Series 391, Washington (1989) 248.
105.   T. Hamieh, M. Rageul-Lescouet, M. Nardin, H. Haı¨dara, J. Schultz, Colloids Surf A Physicochem Eng Asp 125 (1997) 155.
106.    T. Hamieh, J, Schultz, J Chim Phys 93 (1996) 1292.
107. T. Hamieh, J. Toufaily, A. H. Mouneimne, Chromatographia 73 (2011) 99.
108.  V. Gutmann,”the donor acceptor approach to molecular interactions”, Plenum Press,1978,chap:2
109. E. Brendlé and E. Papirer, Journal of colloid and interface science 194 (1997) 217.
110. J. Qiu, K. Matyjaszewski, Macromolecules 30 (1997) 5643.
111. T. E.  Patten, K.  Matyjaszewski, K.; Adv Mater 10 (1998) 901.