Controlling Polymer-Surface Interactions with Random Copolymer Brushes

TLDR

The study presents a simple technique to precisely control interfacial energies and wetting behavior of polymers on solid surfaces. Random copolymer brushes of styrene/methylmethacrylate with varying styrene fraction were synthesized and end‑grafted onto silicon to produce ~5‑nm thick brushes. By varying the styrene fraction, the brushes could tune the relative surface affinities of polystyrene and poly(methylmethacrylate), enabling controlled dewetting and contact‑angle modulation, with equal interfacial energies at f≈0.6.

Abstract

A simple technique for precisely controlling the interfacial energies and wetting behavior of polymers in contact with solid surfaces is described. End-functionalized statistical random copolymers of styrene and methylmethacrylate were synthesized, with the styrene fraction f varying from 0 to 1, and were end-grafted onto silicon substrates to create random copolymer brushes about 5 nanometers thick. For f < 0.7, polystyrene (PS) films (20 nanometers thick) rapidly dewet from the brushes when heated well above the glass transition temperature. The contact angle of the resulting polymer droplets increased monotonically with decreasing f . Similar behavior was observed for poly(methylmethacrylate) (PMMA) films but with an opposite dependence on f . The interfacial energies of the random copolymer brushes with PS and PMMA were equal when f was about 0.6. Thus, precise control of the relative surface affinities of PS and PMMA was possible, demonstrating a way to manipulate polymer-surface interactions.