Flow resistance of a liquid droplet confined between two hydrophobic surfaces

Flow resistance of a liquid droplet confined between two hydrophobic surfaces has been investigated experimentally and factors contributing to the flow resistance have been studied. A water droplet has been sheared between two hydrophobic surfaces and shear resistance has been measured. The experimental results show that the shear resistance at low shear velocities is primarily caused by asymmetrical surface tension due to the contact angle hysteresis. A droplet on a rough hydrophobic surface remains almost symmetrical under shear and exhibits extremely low friction. The shear resistance at high shear velocities is affected by viscous force. Furthermore, sliding angles of water droplets on micropatterned hydrophobic surfaces have been measured to clarify the effects of surface topography on flow resistance. Surfaces with many prismatic structures raised out of the plane tend to exhibit low sliding angles.