title: Water induced hydrophobic surface.
abstract: 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.
authors.forename: Umit
authors.initials: U
authors.lastname: Makal
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Wynne
mesh_terms: D000327:Adsorption; D006827:Hydantoins / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D044085:Microfluidics; D008956:Models, Chemical; D011140:Polyurethanes / Q000737:chemistry*; D013499:Surface Properties; D014867:Water / Q000737:chemistry*; D017155:Wettability
chemical_list: D006827:Hydantoins; D006845:Hydrocarbons, Fluorinated; D011140:Polyurethanes; D014867:Water