Mechanistic investigations of confinement effects on the self-assembly of symmetric amphiphilic copolymers in thin films.

Abstract

The self-assembly of a copolymer thin film, whose molecular structure is composed of one hydrophobic branch and two hydrophilic branches, gives a cylindrical structure consisting of a hydrophobic core and a hydrophilic outer surface. The confinement-induced loss of entropy leads the copolymer to self-assemble into a hexagonal arrangement of cylindrical structures. This hexagonal arrangement is of two induced self-assembly structures under one-dimensional confinement in thin films, i.e., micellar structures with uniform density of an individual core, as well as lamellar structures with two separated hydrophobic layers and one hydrophilic layer. When the repulsive force of the confinement is greater for the hydrophobic polymeric component than for the hydrophilic polymeric component, the self-assembled density of the cores is broad. A proportional change in the individual volume suggests interactions between the walls and the hydrophobic core, which plays a vital role in the formation of the self-assembled structure. A basic understanding of the one-dimensional confinement investigated in this study serves to elucidate the more complex two- and three-dimensional confinements and provides further insights for the design of nanomaterials with novel morphologies.