Tuning the surface hydrophobicity of polymer/nanoparticle composite films in the wenzel regime by composition

Surface hydrophobicity of composite films containing polymer and nanoparticles has been studied as a function of composition. We show that the hydrophobicity can be tuned by adjusting the amount of particles in the two-component system. A sharp transition from a polymer-rich surface to a nanoparticles-rich surface was observed with increasing mass fraction of particles in spin-coated thin films. Water drops on the films did not slide down even at tilt angles of 90 degrees. Contact angle hysteresis increased with the mass fraction of particles indicating that the surface roughness increased as the surfaces remained in the Wenzel regime. Contact angle hysteresis data were quantitatively consistent with predictions of a recent theory.