Contact angle and free surface energy of CdS films on polystyrene substrate

An approach to determination of the contact angle of water, formamide and diethylene glycol droplets (76 +/- 2 degrees, 70 +/- 2 degrees, 69 +/- 2 degrees) and the free surface energy of smooth flat cadmium sulfide films (28 +/- 2 and 33 +/- 2 mN/m by the Owens-Wendt and Wu models, respectively) was proposed. CdS nanoparticles (NPs) were deposited on polystyrene substrates by the chemical bath deposition (CBD) method. The roughness factor of a continuous film of CdS NPs was estimated from contact angles by the Wenzel equation and from scanning electron microscopy images (2.77 and 2.49, respectively). To this end, the surface was made chemically homogeneous by magnetron sputtering of a thin metallic Au-Pd film. The data obtained were used to analyze the wettability of the substrates with CdS NPs in dependence on their roughness as well as the possibility to create superhydrophobic coatings from such NPs. Photovoltaic and photocatalytic properties of the synthesized hydrophilic rough CdS films were demonstrated.