Facile manipulation of receding contact angles of a substrate by roughening and fluorination

Contact angle hysteresis plays a paramount role in anti-smudge surfaces. In this study, surface roughness is systematically altered on some polymeric substrates such as polystyrene and poly(methyl methacrylate) by roughening and its effect on contact angle hysteresis is investigated via measuring advancing and receding contact angles of water. The wettability on these substrates is also modified by vapor-phase deposition of perfluorooctyltrichlorosilane, while the surface morphology is kept the same. As surface roughness is increased, the advancing contact angle grows but three types of the receding contact angle (θ _r ) behavior have been identified: (i) monotonic reduction of θ _r , (ii) monotonic enhancement of θ _r , and (iii) presence of a minimum of θ _r . A plausible mechanism based on the stability of air pockets is proposed to explain our experimental findings. The manipulation of receding contact angles can be achieved based on our findings.