Hydrophobic monolayers on platinum, mica, and silica

Abstract

The wetting behavior of plates of platinum, mica, and silica has been determined after their immersion in aqueous solutions of two anionic and two cationic detergents (sodium cetyl sulfate, potassium laurate, and cetyl trimethylammonium bromide, dodecyl trimethylammonium bromide) over the range of concentrations M to 10 −9 M . In general, a surface becomes hydrophobic to the solution at a low concentration but is completely wetted by a more concentrated solution (ca. 10 −3 M ) of the same compound. The anionic detergents, however, wet silica over the whole range of concentrations. The concentrations which define the limits of the hydrophobic range of solutions have been determined. These are interpreted in terms of adsorption of one or two monolayers of the long-chain ions at the liquid-solid interface.