Polygonal Micellar Aggregates of a Triblock Terpolymer Containing a Liquid Crystalline Block

Abstract

Block copolymers self-assemble in block-selective solvents into diverse nanometer-sized micellar aggregates (MAs). Understanding the formation mechanisms of these morphologies is challenging but important for the design and synthesis of block copolymer architectural materials. Here we report our discovery that polygonal or enclosed cylindrical MAs bearing sharp bends can be formed from a triblock terpolymer containing a liquid crystalline block. We propose that the sharp bends are formed mainly to enable approximately straight sides in which the liquid crystalline packing of the core block is facilitated and the cylinder bending energy is reduced. However, this energy reduction is counteracted by an energy increase due to the concentration of smectic edge dislocations at the vertices. Thus, polygonal MAs are formed only when the toroidal MAs are sufficiently small and the cylinders experience significant bending. We theoretically estimate critical toroidal size below which the transition from round toroids to polygons occurs. This estimated size agrees with our experimental observations, supporting our hypothesis and analysis.