ADSORPTION OF CATIONIC POLYELECTROLYTES ONTO MONTMORILLONITE AND SILICA - MICROCALORIMETRIC STUDY OF THEIR CONFORMATION

Adsorption of various cationic copolymers onto clay and silica particles is investigated through microcalorimetry. On the homogeneous clay surface, the fraction p of adsorbed segments in a homopolyelectrolyte chain is calculated from comparison of the enthalpy of displacement, ΔH, of the polymer molecule with that of the monomer unit. The results are consistent with a frozen-in configuration of the macromolecules at the interface, due to the high adsorption energy of the cationic unit (4 kT). When the ionic content of the chain is decreased, the value of ΔH becomes smaller and smaller and is no longer measurable for nonionic polymers. Considering the evolution of ΔH during monomer adsorption, the silica surface appears heterogeneous. However, the ΔH values observed for the most charged polymers are again constant because only the most reactive surface sites are engaged in the polymer adsorption. © 1990.