Wetting Reversal in Blends of Bottlebrush Copolymers and Linear Homopolymers

In blends of chemically distinct polymers, the surface is usually enriched by the polymer with the lowest surface energy. Herein, we show that when “high energy” bottlebrush copolymers having an approximately equimolar mixture of polystyrene (PS) and poly(2-vinylpyridine) (P2VP) side chains are blended with “low energy” linear PS, the bottlebrush copolymer can enrich the free surface despite an estimated 15% gain in surface energy. This wetting reversal process is mediated by a strong entropic preference for the highly branched bottlebrush architecture at the surface of the blend. The high-energy surface forms spontaneously during film casting when the linear PS chains are much longer than the bottlebrush side chains and is stable through thermal annealing when the lengths of PS side chains, P2VP side chains, and linear PS are optimized. This work demonstrates that for a given commodity polymer, the library of candidate chemistries for the design of surface-active polymer additives is much broader than previously known.