Thermodynamics polymer adsorption

Because we wanted to suppress the effects of thermodynamic quality of the eluent toward the polymer probes, we therefore looked for liquids that would be thermodynamically good solvents for PMMA. At the same time, one solvent should promote polymer adsorption whereas the others should promote desorption. 

As with experimental work on polymer adsorption, experiments in the area of dispersion stability in the presence of polymers require detailed characterisation of the systems under study and the various controlling parameters (discussed above) to be varied in a systematic way. One should seek the answer to several questions. Is the system (thermodynamically) stable If not, what is the nature of the equilibrium state and what are the kinetics of flocculation If it is stable, under what critical conditions ( s, T, x> p etc.) can flocculation be induced ... 

A more comprehensive introduction is Ref. [399], We restrict ourselves to uncharged species and dilute solutions (not binary mixtures). The important subject of polymer adsorption is described in Ref. [400], Adsorption of surfactants is discussed in Ref. [401], Adsorption of ions and formation of surface charges was treated in Chapter 5. In dilute solutions there is no problem in positioning the Gibbs dividing plane, and the analytical surface access is equal to the thermodynamic one, as occurs in the Gibbs equation. For a thorough introduction into this important field of interface science see Ref. [8],... 

Improved understanding of the mechanism, energetics, and structure of the bonding of water to surfaces is needed. Such information is a key to fundamental clarification of the interfacial structure at solid-liquid surfaces. Poor understanding of the thermodynamics of polymer adsorption at interfaces is impeding scientific progress on corrosion inhibition, colloidal stability, alteration of membrane selectivity, and electrocrystallization additives. 

Scheutjens and Fleer (1982) have developed a theory for depletion stabilization and depletion flocculation based upon their statistical thermodynamic approach to polymer adsorption and steric stabilization. This theory is cast in terms of the most primitive model for a polymer molecule, the random flight chain. This weakens the theory in so far as providing quaintitative predictions at the fundamental level for real systems is concerned. The theory does, however, offer qualitative results over a wide range of conditions, being especially powerful in establishing the various trends involved. 

The whole discussion of polymer adsorption so far makes the fundamental assumption that the layer is at thermodynamic equilibrium. The relaxation times measured experimentally for polymer adsorption are very long and this equilibrium hypothesis is in many cases not satisfied [29]. The most striking example is the study of desorption if an adsorbed polymer layer is placed in contact with pure solvent, even after very long times (days) only a small fraction of the chains desorb (roughly 10%) polymer adsorption is thus mostly irreversible. A kinetic theory of polymer adsorption would thus be necessary. A few attempts have been made in this direction but the existing models remain rather rough [30,31]. 

The exact role of the solverrt thermodynamic quality in the polymer adsorption is not well rmderstood though numerous experiments indicate that it plays by far less important role than the solvent strength. Therefore, polymer adsorption in the chromatographic columns is in practice almost exclusively controlled by adjustment of eluent strength. 

It can be concluded that the adsorption processes extensively affect retention volumes in coupled methods of polymer HPLC. Eluent nature (composition) and temperature are the most common tools employed in control of adsorption in the particular polymer - colunm packing system. The thermodynamic quality of eluent likely plays less important role. The statement, which can be formd in the literature ... addition of a nonsolvent to eluent increases polymer adsorption... is misleading. The nonsolvent can be either a desorli or an adsorb for the given polymer so that a nonsolvent present in the solvent mixture can correspondingly either decrease or increase the extent of adsorption of macromolecules. Considerations on the role of conformational entropy of macromolecules in the adsorption processes may help explain some unexpected results in coupled methods of polymer HPLC. 

The second contribution influencing polymer adsorption from solution is the Flory-Huggins interaction parameter between poljnner and solvent. Such an enthalpy of mixing term adds a contribution of X (t)2 z) — 4> ) to the interaction energy contribution, where 4) is the bulk solution concentration of the polymer (2) and, when approaches thermodynamically poor values, then the adsorbed amoimt of pol3mier increases significantly. Figure 5.13 shows experi-... 

This book presents coverage of the dynamics, preparation, application and physico-chemical properties of polymer solutions and colloids. It also covers the adsorption characteristics at and the adhesion properties of polymer surfaces. It is written by 23 contemporary experts within their field. Main headings include Structural ordering in polymer solutions Influence of surface Structure on polymer surface behaviour Advances in preparations and appUcations of polymeric microspheres Latex particle heterogeneity origins, detection, and consequences Electrokinetic behaviour of polymer colloids Interaction of polymer latices with other inorganic colloids Thermodynamic and kinetic aspects of bridging flocculation Metal complexation in polymer systems Adsorption of quaternary ammonium compounds art polymer surfaces Adsorption onto polytetrafluoroethylene from aqueous solutions Adsorption from polymer mixtures at the interface with solids Polymer adsorption at oxide surface Preparation of oxide-coated cellulose fibre The evaluation of acid-base properties of polymer surfaces by wettability measurements. Each chapter is well referenced. 

For any spontaneous process to occur chemical thermodynamics tells us that there must be a lowering of the free energy, AG, of the system. The driving force for polymer adsorption is thus the competition between the net energy change on adsorption (enthalpy of adsorption), the loss of conformational entropy of the adsorbed polymer, and the gain in entropy of solvent molecules released from the surface and polymer upon adsorption. 

Each of these categories has been the subject of extensive experimental and theoretical investigations over the last decades. It would be an unrealistic task to cover in one article all applications of meso-thermodynamics. In particular, we do not consider such important topics as the thermodynamics of adsorption, wetting transitions, microphase separation in polymers, gels, or phase equilibria in confined fluids. Nor do we discuss the increasingly informative simulations of meso-scale systems (see, for example, refs 8, 22 and 23). Instead, in this Chapter we demonstrate only a few characteristic applications of meso-thermodynamics to each category, while emphasizing universality rather than specific details of the phenomena. 

With emulsifiable concentrates, emulsions and microemulsion, the surfactant adsorbs at the oil/water interface, with the hydrophilic head group immersed in the aqueous phase, leaving the hydrocarbon chain in the oil phase. Again, the mechanism of stabilization of emulsions and microemulsions depends on the adsorption and orientation of the surfactant molecules at the liquid/liquid interface. As we will see, macromolecular surfactants (polymers) are nowadays used to stabilize emulsions and hence it is essential to understand their adsorption at the interface. Suffice to say that, at this stage, surfactant adsorption is relatively simpler than polymer adsorption. This is because surfactants consist of a small number of units and they are mostly reversibly adsorbed, allowing one to apply some thermodynamic treatments. In this case, it is possible to describe the adsorption in terms of various interaction parameters such as chain/surface, chain solvent and surface solvent. Moreover, the configuration of the surfactant molecule can be simply described in terms of these possible interactions. In contrast, polymer adsorption is fairly complicated. In addition to the usual adsorption considerations described... 

For most of the present chapter, we can think of the M polymers, very large compared with the ligands, as forming an ideal gas in which the translational and rotational degrees of freedom have been frozen in. This makes the polymers localized, and therefore distinguishable. The release of the polymers from their fixed positions adds the translational-rotational PF and a factor M. These factors do contribute to the PF of the system, but do not change the thermodynamics of adsorption. 

Studying adsorption from solution of polymer mixtimes is of great interest for the theory of PCM because many binders for composites are two-and more-component systems. The presence of two components determines the specificity of the properties of the boundary layers formed by two different polymeric molecules. From another point of view, as the large majority of polymer pairs is thermodynamically immiscible,there may arise interphase layers between two components in the border layer at the interface. The selectivity of adsorption of various components, which is a typical feature of adsorption from mixture, leads to the change in composition of the border layer as compared with composition in the equilibrium solution. This fact, in turn, determines the non-homogeneity in distribution of components in the direction normal to the solid surface, i.e., creates some compositional profile. As compared with stud3ung adsorption from solution of individual polymers, adsorption from mixture is studied insufficiently. The first investigations in this field were done " for immiscible pair PS-PMMA on silica surface, in conditions remote from the phase separation. It... 

In case of immiscible polymer pairs the ternary mixture is more stable thermodynamically (their adsorption on the surface of solid particle is more preferred than that of a miscible polymer pair). This is the basis of the nanocompatibilization (i.e. compatibilization with the aid of nanoparticles). Performance fire retardant system of polypropylene (PP) and phosphorylated epoxy resin (PEP) was reported to improve when montmorillonite nanoclay was introduced. Without nanoclay the distribution of epoxy in PP matrix was inhomogenous, while homogeneous nanodispersion could be achieved after attachment of PEP to clay nanoparticles as interlayer. (8). 

A thermodynamic treatment of polymer adsorption begins by presuming that the chemical potential for a polymer molecule is the sum of the chemical potential for each segment in the molecule. Following this model, the chemical potential for a polymer molecule of A identical segments in solution can be written as the sum of the chemical potentials of each of the i segments ... 

In this chapter, we review the basic mechanisms underlying adsorption of long-chain molecules on solid surfaces such as oxides. We concentrate on the physical aspects of adsorption and summarize the main theories which have been proposed. This chapter should be viewed as a general introduction to the problem of polymer adsorption at thermodynamical equilibrium. For a selection of previous review articles see Refs 1—4, while more detailed treatments are presented in two books on this subject [5,6]. We do not attempt to explain any specific polymer/oxide system and do not emphasize experimental results and techniques. Rather, we detail how concepts taken from statistical thermodynamics and interfacial science can explain general and universal feamres of polymer adsorption. The present chapter deals with equilibrium properties whereas Chapter 3 by Cohen Stuart and de Keizer is about kinetics. 

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