Influence of Component Ratio on Adsorption of Polymer Mixtures under Phase Separation of Solutions

The influence of the component ratio on polymer mixture adsorption in the two-phase condition is estimated. Transition toward the two-phase condition was attained by increasing the solution concentration up to phase separation. For solutions that have separated into two phases with increasing component concentration, the adsorption from each phase has been studied separately and the total adsorption from two phases has been calculated. The polystyrene-poly(butyl methacrylate)-CCl(4) system was investigated using fumed silica as adsorbent. Simultaneously, the fraction of segments of each type that were immobilized by the surface was determined from NMR spectra. In all cases, poly(butyl methacrylate) is characterized by preferential adsorption. The main features of adsorption are similar in both one-phase and two-phase states; however, the values for adsorption and fraction of immobilized segments are different in the case of adsorption from two separated phases because of the difference between the phases in the ratio of components and their concentration in each phase. The distinctions between adsorption from one-phase solutions before phase separation and from solutions modeling separated phases are connected with the redistribution of components between upper and lower phases. As a result, their ratio does not correspond to the initial ratio, and therefore the thermodynamic conditions of solutions, responsible for adsorption, are changed. Because of this, the shape of isotherms of adsorption and the adsorption values are determined by the different levels of aggregation in solutions with various ratios of components. Copyright 1999 Academic Press.