A study of the linear tension effect on the polystyrene microsphere wettability with water

A technique aimed at measuring contact angles for microparticles and suitable for determining the linear tension is developed. The technique is based on determining the "equilibrium" position of the microsphere (where the sum of forces acting on the microsphere is zero) at the liquid-gas interface. This position is unambiguously determined from the experimental force-distance curve obtained for the microparticle-interface interaction. The measurements are performed using an original setup based on the operating principle of the atomic force microscope. The advancing and receding contact angles of water are measured for individual polystyrene microspheres with radii from I to 5 mum. The contact angles are shown to increase with a decreasing microsphere radius, whereas the hysteresis of the contact angle decreases. The results indicate the existence of a negative linear tension in the case of the rough surface of polystyrene microspheres, which is deformed along the three-phase contact line.