RIVAL CONTACT-ANGLE MODELS AND THE SPREADING OF DROPS

The spreading of a drop of viscous fluid on a horizontal surface by capillarity has been studied by a number of authors. Different hypotheses have been advanced for the crucial questions of the contact angle at the moving rim of the drop. It is argued that there is one model that agrees with experiments and is economical in its hypotheses. On the basis of this model, the spreading rate is calculated for small static contact angles and for complete wetting (zero contact angle). The rates are also found when the spreading depends partially or dominantly on gravity.