SIMULATION OF THE STERIC STABILIZATION OF POLYMER COLLOIDS BY DIBLOCK COPOLYMERS

The steric stabilization of polymer colloids by diblock copolymers is simulated on a 22x22x22 cubic lattice with periodic boundary conditions. In the systems described here, the lattice contains 20 chains, the volume fraction of polymer never exceeds 0.0376, and the number of beads in a chain never exceeds 20. The behavior is monitored by evaluation of the dimensionless ratios M(n)/M(o) and M(w)/M(n), where M(o) is the mass of an individual chain, and M(n) and M(w) are the number- and weight-average molecular weights of the particles in the system. By suitable variation in the pairwise interaction energies, one can cause the system to (1) establish a dynamic equilibrium, in which aggregates easily form and dissociate, (2) follow an irreversible path toward the formation of the largest possible aggregate, or (3) reach a long-lived metastable state in which the system prefers smaller aggregates than those that would exist at a true equilibrium. The metastable state arises from the steric stabilization of the dispersed state, as is shown by its characteristic response to the variation in the size of the soluble (stabilizing) block, at constant size of the insoluble block and constant interaction energies. The simulation also documents an interesting influence of the energy of the self-interaction of the insoluble block on the efficiency of the steric stabilization of the metastable state.