BINARY POLYMER BRUSH IN A SOLVENT

We have studied the equilibrium structure of a grafted polymer layer c omposed of two distinct species of homopolymers, the ''binary brush'', in various solvent conditions. By using a coarse-grained simulation m ethod that involves direct calculation of the Edwards hamiltonian, we are able to simulate much larger systems than would otherwise be possi ble with a more standard lattice simulation. If the two species are ma de sufficiently immiscible, we find lateral binary microphase separati on over a wide range of solvent conditions. Due to the presence of sol vent, we find a stage where the brush expands in a laterally homogeneo us manner as immiscibility increases. In this stage, laterally average d quantities are well-described by a single solvent-related parameter: a modified excluded volume parameter. This is followed by lateral mic rophase separation in which the brush volume remains relatively consta nt. In Theta solvent, this phase separation sets in at a degree of imm iscibility consistent with a mean field prediction for melt layers. Th e onset of phase separation is delayed as solvent quality increases. F urthermore, a reduction in solvent quality results in a stronger cross over between mixed and phase-separated configurations. Under poor solv ent conditions, we find interesting structural variations as a result of the combination of phase separation from solvent and phase separati on of the two species.