(228g) Phase Diagrams of Symmetric Diblock Copolymers Confined between Two Homogeneous Surfaces

For symmetric diblock copolymers confined between two flat and homogeneous surfaces, three types of self-assembled morphologies (parallel, perpendicular, and mixed lamellae) have been observed in experiments. While the effects of surface preference (for one of the two blocks) and film thickness on the thin-film morphology are well understood, less studied is the influence of a hard (impenetrable) surface on the copolymer chain conformations, referred to as the "hard-surface effects". It is these effects that favor the perpendicular lamellae between two neutral surfaces over parallel lamellae, at all film thicknesses. They also lead to the formation of mixed lamellae between asymmetric surfaces (not antisymmetric ones where the two surfaces prefer different blocks with the same strength).

Here we perform self-consistent field (SCF) calculations in continuum to map out the phase diagrams of symmetric diblock copolymers confined between two homogeneous surfaces, as a function of the two surface preferences and the film thickness. The SCF equations are solved in real space with high accuracy. The hard-surface effects on the chain conformations and thin-film morphology are studied in detail. We also examine the chain conformations at the T-junction in the mixed lamellae, representing one type of defects commonly seen in lamellar systems. Three types of mixed lamellae are found as stable phases over a wide range in the phase diagrams. Finally, we compare our results with previous experimental, theoretical, and Monte Carlo studies.