F-0527 Friction characteristics of a microdroplet on hydrophobic surfaces

Abstract

This paper describes the normal and tangential reaction forces of a microdroplet between two hydrophobic surfaces. Two parallel glass plates were coated with fluoric coating material in order to get hydrophobic characteristic. These surfaces show about 150° in contact angle against water droplet and l〜2μm Ra in surface roughness. The amount of water is 0.7〜6μl. With changing the distance between the two surfaces, the repulsive meniscus force and the friction force were measured and the shape of the droplet was observed. Meniscus force increases as the two surfaces get closer. Measurable maximum load capacity of 1.7μl droplet is 20mN with distance of 30μm. The meniscus force shows hysteretic characteristic and adhesive force is generated when the two surfaces are separated. On the other hand friction forces varied with respect to time. The cause of these results is considered that the water was partially held by the surface valleys when the normal load was applied.