Water Induced Hydrophobic Surface

by Umit Makal & Kenneth J. Wynne Langmuir, 31 Mar 2005 (web release) A polyurethane coating is described that has hydrophilic wetting behavior when dry and hydrophobic when wet. A difference of ~25 in advancing contact angles for dry and wet 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. Read the article