Molecular-aggregative mechanism of adsorption

The peculiarity of polymer adsorption, connected with its aggregative mechanism, consists in the fact that at each concentration of solution in adsorbent presence, a new state of equilibrium between isolated and aggregated molecules is established. To each point of isotherm corresponds another structure of adsorbing units (from isolated macromolecules up to aggregates of various size) 

It is evident that when this mechanism is operative, the structure and thickness of adsorption layers are determined by the structure and size of aggregates, and by the ratio between aggregated and isolated macromolecules in the layer. Killmann calculated the thicknesses of adsorption layers of poly(methyl methacrylate) and some other pol3rmers based on comparison of the amount of adsorbed polymer and surface of an adsorbent (adsorption from concentrated solutions (up to 56.0 g/1)). The values found are of the order of 0.7 mcm, which essentially exceeds the thickness of a monolayer. For solutions of isotactic polystyrene and other pol3rmers on disperse powders, the thicknesses were found in the range of 1-8 mcm, which may be explained by adsorption of aggregates. The thick- 

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 analyzing the data on adsorption from a mixture, a solution of mixture of two polymers in a common solvent should be treated as a solution of polymer A in solution of polymer B and at the same time as a solution of polymer B in solution of pol5uner A. Accordingly, the thermodynamic quality of the mixed sol- 

interpretation of the experimental evidence on adsorption from mixture is complicated by the thermodynamic quality of the solvent, and for either pol3rmer, it differs from that for the other pol3rmer and varies with the concentration of the latter. If the problem of adsorption of mixtures is approached on the basis of the concept of a dilute and semi-dilute solutions, then it is obvious that conditions of aggregation and adsorption should also depend on the critical concentration of overlapping of coils, i.e., on the concentration at which coils of the component macromolecules start touching and overlapping one another. It is clear that the values C for individual components in the solvent cannot be used here, since in the solution of a mixture, the thermodynamic quality of the mixed solvent differs from that of the pure solvent and depends on the concen- 

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