Resistance to Flow in Capillary Systems of Positive Contact Angle
Contact Angle, Wettability and Adhesion, volume 43 of Advances in Chemistry, page 250--267. American Chemical Society, (1964)DOI: 10.1021/ba-1964-0043
Abstract
In capillary systems having an equilibrium contact angle substantially greater than zero, the liquid-solid-vapor boundary line shows a definite resistance against being moved along the solid surface. This resistance is characterized and defined as the critical line force. By determining the pressure necessary to start an index of liquid moving in a tube made of the substrate material, the critical line force values of a series of liquids on Teflon and polyethylene substrates were determined and found to increase linearly as cos θequi1 decreased. In so far as cos θequi1 remained a linear function of γLA, the contact angle hysteresis increased monotonically, but not linearly, with increasing critical line force. These findings support the view that microscopic surface roughness cannot be the sole factor controlling contact angle hysteresis.