Adsorption kinetics of hydrophobic polysoaps at the methylene chloride–water interface

The kinetics of the adsorption of hydrophobic insoluble in water polymers (ammonio polymethylmethacrylates, known as Eudragits RL and RS) at the methylene chloride (MC)–water interface has been studied in function of their bulk concentration in the organic phase. These polymers, conventionally denoted as hydrophobic polysoaps, strongly adsorb at the oil–water interface by immersing their ionisable (trimethylammonium (TMA)) groups into the water phase. Unlike the hydrophilic polysoaps (the water-soluble hydrophobically modified polyelectrolytes) whose adsorption at the oil–water interface is controlled by the hydrophobic effect (the gain in entropy due to the destruction of the ordered layers of the water molecules around the adsorbed alkyl chains), the driving force for the adsorption of hydrophobic polysoaps is the gain in enthalpy due to the hydration of adsorbed hydrophilic groups of the polymer. been shown that the dynamic interfacial tension curves γ(t) of hydrophobic polysoaps are characterized by several stages of adsorption with different characteristic relaxation times. During the lag-stage and the post lag-stage the adsorption is the diffusion-controlled process of macromolecules from the bulk of the organic solution to the interface. At the final stage, the adsorption is characterized by much lower rate due to the steric hindrance exerted by the yet formed adsorption layer with regard to newly adsorbing macromolecules.