E. Rame, THE INTERPRETATION OF DYNAMIC CONTACT ANGLES MEASURED BY THE WILHELMYPLATE METHOD, Journal of colloid and interface science, 185(1), 1997, pp. 245-251
We present an analysis for properly interpreting apparent dynamic cont
act angles measured using the Wilhelmy plate method at low capillary n
umbers, Ca. This analysis removes the ambiguity in current dynamic mea
surements which interpret data with the same formula as static measure
ments. We properly account for all forces, including viscous forces, a
cting on the plate as it moves into or out of a liquid bath. Our main
result, valid at O(1) as Ca --> 0, relates the apparent dynamic contac
t angle to material-dependent, geometry-independent parameters necessa
ry for describing dynamic wetting of a system. The special case of the
apparent contact angle = pi/2 was solved to O(Ca). This O(Ca) solutio
n can guide numerical work necessary for higher Ca's and arbitrary val
ues of the apparent contact angle. These results make the Wilhelmy pla
te a viable method for determining material parameters for dynamic spr
eading. (C) 1997 Academic Press