Characterisation of surface modified polystyrene particles by microcalorimetry and liquid sorption

Abstract

Different types of polystyrene particles were investigated by titration microcalorimetry and selective liquid sorption from 1-propanol(1)–water(2) mixtures. The first type of polymer particles is related to sulfonated polystyrene macrobeads of different surface charge. The other types are colloidal polystyrene particles: One of these is type-3-latices prepared by emulsion copolymerisation of styrene and sodium styrene sulfonate with potassium peroxodisulfate as the initiator. The second type of colloidal polystyrene particles is formed by a ground macroreticular ion exchange resin (Amberlyst 15). The adsorption measurements were performed in 1-propanol–water mixtures and were documented by composite isotherms. The composite isotherms found for all three types of polystyrene particles are S-shaped in character. Water is preferentially sorbed up to water mole fractions x 2 ≈ 0.80. The mole fraction of the adsorbed layer ( x s 2) was calculated from the surface excess and equilibrium diagrams ( x s 2/ x 2) are presented. The enthalpy effect accompanying the solvent exchange was determined by titration microcalorimetry. Changes in the conformation of the macromolecular frame were found to be an endothermic effect which is overlapped by the exothermic process of water displacement. The enthalpy of displacement isotherms fairly well reveal differences in the swelling ability of the particles surfaces. The change in free enthalpy was calculated from adsorption data from which entropy functions for the exchange process can be calculated. In view of the thermodynamic potential functions structural changes in the adsorption layer and formation of alcohol water clusters on the surfaces of the colloidal polystyrene particles may play an important role in the dispersion stability.