Water induced hydrophobic surface.

A polyurethane coating is described that has hydrophilic wetting behavior when dry and hydrophobic when wet. A difference of approximately 25 degrees in advancing contact angles for dry (83 degrees ) and wet (108 degrees ) states is found by sessile drop and dynamic methods. The term "contraphilic" is suggested for this reversible change opposite customary amphiphilic behavior. Contraphilic behavior results from a soft block containing semifluorinated and 5,5-dimethyhydantoin segmers. Amide inter/intramolecular hydrogen bonding is proposed for the hydrophilic (dry) state, while surface-confined, amide-water hydrogen bonding "releases"semifluorinated groups, giving the hydrophobic state. Water-induced hydrophobic surfaces may lead to applications for easily switched wetting, such as in microfluidics.