G. Mason et Nr. Morrow, EFFECT OF CONTACT-ANGLE ON CAPILLARY DISPLACEMENT CURVATURES IN PORE THROATS FORMED BY SPHERES, Journal of colloid and interface science, 168(1), 1994, pp. 130-141
The curvature of an interface in a pore depends upon the shape of the
pore and the operative contact angle that the interface makes with the
solid surface. Even relatively simple pores formed by the surfaces of
equal spheres have a complex shape including nonaxisymmetric cross-se
ction and converging-diverging geometry. For such pores, a theory for
meniscus behavior has been devised that uses a combination of a theory
for meniscus curvature in rods together with the toroidal approximati
on of Purcell. The results of the theory show that converging-divergin
g geometry tends to compensate for the effect of contact angle. This i
s because the position at which the nonzero contact angle meniscus has
maximum curvature in a converging-diverging pore is not the narrowest
part of the pore throat. Due to this compensation, the effect of cont
act angle on maximum meniscus curvatures for drainage is approximately
proportional to cos 2/3 theta (rather than the cos theta appropriate
for cylindrical tubes). Experiments on pores formed by PTFE spheres us
ing partially wetting liquids confirmed the theoretical prediction. Co
ntact angle measurements on the PTFE spheres also demonstrated that, b
ecause of microscopic surface roughness, receding contact angles (thes
e being operative with respect to drainage) on ground surfaces are sig
nificantly lower than values for smooth surfaces. (C) 1994 Academic Pr
ess, Inc.