GRADIENT MEASUREMENTS OF PHASE BEHAVIOR IN THIN FILMS OF BLOCK COPOLYMER AND HOMOPOLYMER BLENDS

Abstract

The aim of this work is to test a novel high-throughput method of producing homopolymer:block copolymer blended thin films. The use of a flow-coater to create thickness gradient films offers the possibility of laying down the homopolymer and copolymer separately and then blending via annealing. This approach creates a continuous composition gradient across the film, offering a more efficient route to sample preparation compared to the traditional method of casting films from blend solutions. The work is focused on the blending of various polystyrene homopolymers with a single sphere-forming poly(styrene)-poly(hexylmethacrylate) diblock copolymer. Analyzing atomic force micrographs of such gradient films reveals the feasibility of this alternative method of blend preparation. Samples produced using both the novel bilayer route and the traditional solvent-cast films exhibited patterns indicating that complete blending was not occurring, i.e., the block copolymer and homopolymer were not fully miscible. It is believed that these samples approach a transition from a homogeneous blended state to a macrophase separated state, and since the free energy differences associated with how the macrophase-separated homopolymer is distributed are small, the two preparation routes can yield apparently different structures, a reflection that the equilibrium state is not a single-phase mixture. In cases where the equilibrium structure is a single-phase mixture, it is expected that these two methods would provide equivalent methods of blending.