First-order wetting transition at finite contact angle.

The wetting of a polymer brush by a melt of similar chains can have a window of complete wetting with a classical allophobic wetting transition at low grafting density sigma and an autophobic one at high sigma. However, when the melt chains are much longer than the brush chains, the contact angle alpha goes through a nonzero minimum where partial differential alpha/ partial differential sigma has a jump. A self-consistent-field analysis and experimental observations indicate a double-well disjoining pressure curve, consistent with a first-order wetting transition at finite alpha. The metastable contact angle can become zero.