E. Rame et S. Garoff, MICROSCOPIC AND MACROSCOPIC DYNAMIC INTERFACE SHAPES AND THE INTERPRETATION OF DYNAMIC CONTACT ANGLES, Journal of colloid and interface science, 177(1), 1996, pp. 234-244
We have studied shapes of dynamic fluid interfaces at distances less t
han or equal to 1700 mu m from the moving contact line at capillary nu
mbers (Ca) ranging from 10(-3) to 10(-1). Near the moving contact line
where viscous deformation is important, an analysis valid to O(1) in
Ca describes the shape of the fluid interface. Static capillarity shou
ld describe the interface shape far from the contact line. We have qua
ntitatively determined the extent of the regions described by the anal
ysis with viscous deformation and bq a static shape as a function of C
a. We observe a third portion of the interface between the two regions
cited above, which is not described by either the analysis with visco
us deformation or a static shape. In this third region the interface s
hape is controlled by viscous and gravitational forces of comparable m
agnitude. We detect significant viscous deformation even far from the
contact line at Ca greater than or similar to 0.01, Our measured dynam
ic contact angle parameter extracted by fitting the analysis with visc
ous deformation to the shape near the moving contact line coincides wi
th the contact angle of the static-like shape far from the contact lin
e. We measure and explain the discrepancy between this dynamic contact
angle parameter and the apparent contact angles based on meniscus or
apex: heights. Our observations of viscous effects at large distances
from the contact line have implications for dynamic contact angle meas
urements in capillary tubes. (C) 1996 Academic Press, Inc.