Droplet dynamics on a hydrophobic surface coated with N-octadecane phase change material

Water droplet mobility on the inclined hydrophobic surface coated with n-octadecane phase change material is examined. Polycarbonate surface is initially crystallized and later nano-size functionalized silica particles are deposited on the crystallized surface to increase the water droplet contact angle and reduce the contact angle hysteresis. Reversible exchange of wetting state is achieved via introducing a thin film of n-octadecane phase change material with 1.5 μm thickness on the functionalized silica particles deposited surface. The resulting surface remains hydrophobic if n-octadecane is in the solid phase while it becomes hydrophilic if thin film remains in the liquid phase. The surface wetting state reversibly exchanges during melting and re-solidification of n-octadecane film. Water droplet undergoes rolling and sliding on the inclined hydrophobic surface if n-octadecane is in solid phase. In this case, the solid n-octadecane flakes are formed on the surface and the functionalized silica particles deposited surface exposes to the free surface from the close regions of the flakes. This gives rise to a hydrophobic characteristic on the surface with droplet contact angle 140° and contact angle hysteresis 8°. Droplet rolling and sliding are influenced by the solid flake distribution on the n-octadecane coated surface. The closely spaced solid flakes results in hydrophilic surface while contributing to the droplet sliding on the inclined surface, which is more pronounced for large volume droplets.