Orientational transitions in symmetric diblock copolymers on rough surfaces

TL;DR

This paper develops a model to predict how symmetric diblock copolymers change their lamellar orientation when in contact with rough surfaces, considering surface roughness and polymer properties, and validates it with experimental data.

Contribution

It provides an analytical expression for the orientation transition of block copolymers on rough surfaces, linking surface roughness, polymer periodicity, and orientation behavior.

Findings

Analytical expression for orientation transition derived.

Model agrees well with experimental data.

Surface roughness influences lamellar orientation.

Abstract

We present a model addressing the orientation transition of symmetric block copolymers such as PS/PMMA on smooth and rough surfaces. The distortion free energy of parallel and perpendicular lamellar phases in contact with a rough solid surface is calculated as function of the surface roughness amplitude and wavelength, as well as the polymer lamellar periodicity (molecular weight). We find an analytical expression for the orientation transition. This expression is compared and agrees well with recent experiments done with six different polymer molecular weights and surface preparations.