Effect of dynamic contact angle on capillary rise phenomena

Capillary rise experiments of different liquids in glass capillaries and in columns of packed powders were carried out. The analysis of this rise was performed according to the classical Washburn's equation in which the calculation of a constant term is needed in order to be able to determine contact angle of the considered liquid on the capillary wall or powders. However, it was observed that this constant term apparently varies as a function of the liquid used, in contradiction with Washburn's approach. A more fundamental study of alkane rise into glass capillaries was carried out showing that this apparent variation is due to the variation of contact angles, which can take large values (up to 60 degrees) as a function of velocity of the liquid front, although their expected value is 0 degrees. Therefore, in the case of powders, different approaches to determine the real constant term: with respect to particle size are proposed. Consequently, the use of Washburn's equation for the determination of contact angles of liquids on these powders is also discussed. (C) 2000 Elsevier Science B.V. All rights reserved.