DIBLOCK COPOLYMER MICROEMULSIONS - A SCALING MODEL

The properties of diblock copolymers as emulsifiers of immiscible and highly selective solvents are investigated using a scaling model. Solvent selectivity leads to copolymer aggregation at the liquid-liquid interface and the formation of stable microdomains. We find that symmetrical copolymers form lamellae at all copolymer concentrations. Asymmetrical copolymers, however, aggregate in spherical microdomains at equilibrium with the two bulk solvent phases. The interface curvature and the surface density increase, and the volume of the emulsion phase volume decreases, with the copolymer degree of asymmetry. The critical aggregation concentration is found to be significantly lower than the critical micelle concentration (cmc). The emulsion phase volume increases linearly with copolymer concentration, until, when one of the solvents is exhausted, cylindrical domains appear. At high copolymer concentrations lamellae replace the cylindrical droplets.