Contact angle determined by spontaneous dynamic capillary

We investigate spontaneous dynamic capillary rises of liquids. While the liquid front rises spontaneously and vertically in a capillary, hydrostatic effects become more and more important. We theoretically derive new equations for capillary rises with hydrostatic effects, in order to describe the relation between the liquid front height and time, which enables us to experimentally measure contact angles of capillary tube surfaces directly. Excellent agreement between our theory and experiment shows the validity of the proposed method. Thus, it becomes possible to measure the wettability of small particles as well as porous materials. (c) 2006 Elsevier B.V. All rights reserved.