Dynamics of the contact line: Contact angle hysteresis

An effective dynamic for the edge of a three-dimensional sessile drop is derived from the capillary waves model of two-dimensional interfaces. The corresponding Monte Carlo evolution is implemented to study wetting of a disordered substrate. Hysteresis associated with a stick-slip mechanism is measured as a function of disorder and system size. For a given system size, no measurable hysteresis is found at weak disorder. For a given disorder, even small, a measurable contact angle hysteresis is found above a certain system size. [S0031-9007(97)04480-3].