Effect of Block Length on Solvent Response of Block Copolymer Brushes: Combinatorial Study with Block Copolymer Brush Gradients

Abstract

Block copolymer (BC) brush gradient libraries were examined as high-throughput platforms to study the effect of relative block lengths on the response to solvents. BC brushes of poly(n-butyl methacrylate) (PBMA) and poly(2-(N,N‘-dimethylamino)ethyl methacrylate) (PDMAEMA) were synthesized via surface-initiated atom transfer radical polymerization (ATRP). The gradient libraries had uniform bottom PBMA blocks and molecular mass gradient top PDMAEMA blocks. The rearrangement of the BC brushes upon exposure to water and hexane was assessed by water contact angle (θw) measurements. θw mapping of each gradient library illustrated how the top PDMAEMA block length influenced the response of BC brushes to solvents. Comparison among libraries with different bottom PBMA thicknesses revealed how the bottom block length affected the solvent response of BC brushes. Our results indicate that the solvent response behavior of the BC brushes is greatly influenced by their relative block lengths. While surface response properties can be suppressed by a long top block, they can be enhanced by the extension of the bottom block. In addition, our work suggests that BC brushes could be fabricated to provide tunable surfaces with gradient responsive properties.