Surface-Initiated Polymerization of Superhydrophobic Polymethylene

We report a new surface-initiated polymerization strategy that yields superhydrophobic polymethylene (PM) films from initially smooth substrates of gold and silicon. The films are prepared by assembling a vinyl-terminated self-assembled monolayer, followed by exposure of the surface to a 0.1 M solution of borane, and polymerizing from the borane sites upon exposure to a solution of diazomethane at −17 °C. Surface-initiated polymethylenation (SIPM) presents rapid growth in relation to other surface-initiated reactions, producing PM films thicker than 500 nm after 2 min of reaction and 3 μm after 24 h of reaction. AFM and SEM images show the presence of micro- and nanoscale features that enable the entrapment of air when exposed to water. Consistent with this result, these films exhibit advancing water contact angles greater than 160°, dramatically different than 103° measured for smooth PM films, and hysteresis values ranging from 2° to 40°, depending on the substrate and polymerization time. The superhydrophobic character of the films results in the entrapment of air at the polymer/solution interface to provide remarkable resistances greater than 1010 Ω·cm2 against the transport of aqueous redox probes and cause the film to behave as a “perfect” capacitor.