Tunable Microstructure and Nanomechanical Properties in a Binary Polymer Brush

INTRODUCTION The next generation of sophisticated nanomachines is being designed with integrated mechanical, optical, chemical gating, and biological devices to perform complex sensing functions. Such systems require “adaptive surfaces”, or surfaces that have the ability to respond to external stimulus and have their surface properties tuned for necessary functionality. Polymer brushes are prospective materials for such applications because as a result of the high grafting density and uniformity in composition and chain height throughout the brush, the layer responds communally to very subtle changes in the surrounding environment such as pH or solvent quality. For a binary polymer brush layer, we investigate the morphological state, the structure reordering, and the nanomechanical properties as a function of treatment with a wide range of solvents. Two incompatible polymers, polymethylacrylate (PMA) and poly(styrene-co-2,3,4,5,6-pentafluorostyrene) (PSF), were randomly grafted one after another onto a silicon wafer via the “grafting from” method producing thick (20 – 150 nm) dense mixed brush layers. The resulting layers possessed a nanostructured surface exhibiting either lateral, or vertical microphase segregation of the two components.