RHEOLOGICAL BEHAVIOR OF SOLUTIONS OF AMPHIPHILIC ACRYLIC COPOLYMERS IN MIXED-SOLVENTS

A descriptive model was developed, using viscometry and light scatteri ng, that explains the anomalous theological behavior of solutions of a mphiphilic acrylic copolymers upon the addition of water. The theologi cal behavior can be explained by considering the relative magnitudes o f three interactions: the intra- and intermolecular electrostatic inte ractions between the ionizable acid groups in the copolymer, the intra molecular hydrophobic interactions, and the intermolecular hydrophobic interactions. The initial addition of water enhances the ionization o f the acid groups, causing the electrostatic interactions between the acid groups to dominate the other two interactions. This leads to expa nsion of the polymer molecules and, consequently, to a relatively cons tant viscosity during dilution with water. Upon attaining the maximum ionization of the acid groups on the chain, the intramolecular hydroph obic interactions dominate the electrostatic repulsion, and the chains start to contract. Further addition of water leads to aggregation of the polymer chains into large polymolecular domains, resulting in a sh arp decrease in the viscosity. Intermolecular hydrophobic interactions dominate the theological behavior in this stage of water dilution. (C ) 1996 John Wiley & Sons, Inc.