Computer-aided comparative investigation of architecture influence on block copolymer phase diagrams

Abstract

The microphase separation in melts of asymmetric triblock and trigraft, periodic polyblock and polygraft, and star-shaped copolymers of two types ((An)k(Bm)k and (AnBm)k) is investigated within the framework of the mean field approximation. To enable rapid comparison of the behavior of various types of block copolymer architecture, a special program 'Supercrystal using previously calculated higher correlators of specific systems is elaborated. Surfaces of phase transition between phases with different supercrystal symmetry and a spatially homogeneous state are constructed as a function of molecular architecture and the Flory parameter x. A behavior similar to a tricritical one is observed in melts of star-shaped copolymers of the kind (A,)k(B,)k with k > 5, k being the number of arms. Phase diagrams obtained for the other systems are like the phase dmam obtained by Leibler for the molten diblock copolymer, but the temperatures of the phase transitions differ considerably for copolymers consisting of the same blocke connected in a different manner. There are limiting phase diagrams for both polyblock and polygraft systems in the limit k - OD, k being the number of blocks A,B, in a chain.