Powder dynamic contact angle measurements: Young contact angles and effectively wet perimeters

Dynamic contact angle (DCA) measurements on powder are of great interest for the prediction of various processes. Powder covered slides exhibit rough surfaces on which the definition of the Young contact angle is not straightforward. This paper proposes a semi-empirical model, which relates the Young contact angle to the measured immersion load of rough slides: Delta F-0 = gamma(LV) x [P + cos theta(Y) x p(0)]. An effective wet perimeter, p(0), is introduced as well as a mean contact line resistance, P x gamma(LV). Both factors appear to describe well experimental measurements on test surfaces where various defects are created. As a result, DCA measurements can be adapted to any powder from very fine to very large, as proved on lactose powder and granules. (C) 1998 Elsevier Science S.A. All rights reserved.