Wetting Reversal in Blends of Bottlebrush Copolymers\nand Linear Homopolymers

In blends of chemically distinct\npolymers, the surface is usually\nenriched by the polymer with the lowest surface energy. Herein, we\nshow that when “high energy” bottlebrush copolymers\nhaving an approximately equimolar mixture of polystyrene (PS) and\npoly(2-vinylpyridine) (P2VP) side chains are blended with “low\nenergy” linear PS, the bottlebrush copolymer can enrich the\nfree surface despite an estimated 15% gain in surface energy. This\nwetting reversal process is mediated by a strong entropic preference\nfor the highly branched bottlebrush architecture at the surface of\nthe blend. The high-energy surface forms spontaneously during film\ncasting when the linear PS chains are much longer than the bottlebrush\nside chains and is stable through thermal annealing when the lengths\nof PS side chains, P2VP side chains, and linear PS are optimized.\nThis work demonstrates that for a given commodity polymer, the library\nof candidate chemistries for the design of surface-active polymer\nadditives is much broader than previously known.