Surface etching of silicone elastomers by depolymerization

Abstract

Silicone elastomer surfaces that are rough at the nanometer to micron scales could be useful for biomaterials, but there are few efficient routes for their preparation. Silicones undergo depolymerization under equilibrating conditions. We demonstrate that surface roughness can be induced by depolymerizing silicone elastomers using triflic acid, tetrabutylammonium fluoride or KOH as catalysts. The efficiency of depolymerization, however, is decoupled from the roughness that develops. When the catalysts are dissolved in solvents that do not effectively swell silicones, the etching reaction can be mostly directed to the elastomer surface. Acid catalysis leads to slow, nearly homogenous surface erosion with surface roughnesses only increasing from 15 to about 125 nm root mean squared roughness. By contrast, once KOH partitions into the elastomer, the rate of erosion is more efficient than return of the catalyst to the solvent, leading to deep channels and roughnesses of up to ∼850 nm. The use of fluoride requires good solvents for silicone, and leads to surfaces of intermediate roughness. Thus, judicious choice of catalyst and solvent permits independent control over depolymerization and the induction of surface roughness.