Nonequilibrium Dynamics in Symmetric Diblock Copolymer Systems

Abstract

In this dissertation, experiments are described which elucidate how the ordering of symmetric diblock copolymers affects the dynamics within various geometries. In all studies presented herein, experimental techniques are used to probe the dynamics of symmetric diblock copolymer systems as they progress toward equilibrium and to study the role that nanoscale ordering plays in these processes.

In the majority of work presented herein, experiments were performed on symmetric diblock copolymer thin films. This work focuses on the effect of various sample preparation techniques on the equilibration kinetics of lamellar forming films. Films are prepared with varying thicknesses in the homogeneous, disordered state and annealed to form islands and holes as the surface decomposes to form commensurate thicknesses. Both nucleated and spinodal growth patterns were observed for this surface decomposition dependent on the initial thickness and intermediate morphologies formed upon ordering. We also prepare equilibrium commensurate films and induce a step change in surface interactions, switching from asymmetric to symmetric wetting boundaries. Upon equilibration, a perforated lamella forms at the free surface to mediate the order-order transition, inducing hole growth with a ramified shape.

In the final project, the effect that lamellar order has on dynamics is studied within unstable polymer melt bridges. Liquid bridges are what is formed when a droplet is stretched between two surfaces, like spit between two fingers. Disordered diblock bridges are shown to evolve similar to their homopolymer counterparts. However, ordered diblock copolymer exhibits an enhanced stability with an inhibition of flow proposed to be induced by the isotropic orientational order within the bridge. As well, shear thinning is observed that is believed to be caused by an alignment of ordered domains along the bridge axis due to shear strain rates, providing pathways for flow of diblock copolymer out of the unstable bridge.