Spreading of Block Copolymer Films and Domain Alignment at Moving Terrace Steps

TL;DR

This paper studies how phase-separated block copolymer films spread, revealing that early spreading is controlled by activated flow at terrace steps, while later spreading follows a diffusion-like behavior, leading to aligned domain patterns.

Contribution

It introduces a new understanding of spreading dynamics in copolymer films, highlighting the role of terrace steps and domain alignment mechanisms.

Findings

Early spreading rate is controlled by activated flow at terrace steps.

Late spreading follows a diffusion-like $t^{-1/2}$ dependence.

Chain hopping leads to defect-free domain alignment on terraces.

Abstract

We investigate spreading of phase separated copolymer films, where domain walls and thickness steps influence polymer flow. We show that at early stages of spreading its rate is determined by slow activated flow at terrace steps (i.e. thickness steps). At late stages of spreading, on the other hand, the rate is determined by the flow along terraces, with diffusion-like time dependence $t^{-1/2}$. This dependence is similar to de Gennes and Cazabat's prediction for generic layered liquids, as opposed to the classical Tanner's law of drop spreading. We also argue that chain hopping at the spreading terrace steps should lead to the formation of aligned, defect-free domain patterns on the growing terraces.