Compressibility of Colloids: I. Compressibility Studies of Aqueous Solutions of Amphiphilic Polymers and Their Adsorbed State on Polystyrne Latex Dispersions by Ultrasonic Velocity Measurements

摘要

Sound velocity measurements were made to obtain compressibility values at 2 MHz, and to investigate the influence of the interface in dispersions of electrostatically stablized dispersions. The measurements were on aqueous dispersions of polystyrene latex as a function of volume concentration up to 49% and temperature up to 80 C (approaching the glass transition temperature), and in solutions of 72.5%, and 78% hydrolyzed polyvinyl alcohol-polyvinyl acetate block copolymers (PVA) as a function of temperature above and below their cloud points. The measurements were extended to latex coated with PVA under conditions known to give a 30 nm layer at room temperature. These dispersions give a resultant compressibility lower than expected from the simple additive effect of the separate components at 25 C and higher. The decrease in compressibility may be due to either or both of two effects: the hydrophobic interaction between the acetate groups and the polymer backbone of the polystyrene latex results in a more rigid structure, and the suppression by the PVA coating of the association-dissociation reaction responsible for the remarkable high adsorption of ultrasound will result in a lower compressibility. (Author)