Jg. Petrov et Rv. Sedev, QUASI-STATIC SHAPE OF THE STEADY MOVING MENISCUS - COMPARISON OF THE APPARENT AND EXTRAPOLATED DYNAMIC CONTACT ANGLES, Colloids and surfaces. A, Physicochemical and engineering aspects, 74(2-3), 1993, pp. 233-241
The present investigation compares apparent dynamic contact angles, ev
aluated from dynamic capillary heights via the corresponding static re
lationships, and extrapolated contact angles deduced from dynamic meni
scus profiles fitted with the Laplace equation. A siliconized glass cy
linder and a thin filament vertically withdrawn from glycerol-water mi
xtures are studied as being representative of the two limiting cases o
f very low and high azimuthal curvature. Published data for plunging o
f a hydrophobic tape (flat wall) into similar mixtures are also discus
sed. It is found that all steady menisci considered are adequately des
cribed by the Laplace equation with the exception of the point at the
solid wall. Thus, apparent contact angles, which are larger than the e
xtrapolated ones, are found in all cases. This difference is small, bu
t significantly exceeds the experimental error; it indicates a hydrody
namic deformation close to the contact line. The thickness of this def
ormation is estimated from the deviation between the extrapolated Lapl
acian fitting curve and the actual dynamic profile of the fluid interf
ace. For the systems and conditions studied (capillary number, Ca < 0.
15) the thickness of this deformation is 3-5% of the maximum static ca
pillary height.