Capillary phenomena. Part 10.—Behaviour of grooved rods at fluid/fluid interfaces

Abstract

The force–displacement behaviour at a fluid/fluid interface is described for a vertically-positioned cylindrical solid, with recurring horizontal grooves, i.e., the solid consists of truncated cones alternately joined at pairs of smaller and larger faces. When the grooves are relatively large, the excess applied force needed to withdraw and immerse the rod shows loops with irreversible jumps as a function of displacement. These are explained in terms of stability and instability where the fluid/fluid interface meets the solid: at outer-edge, inner-waist and upper-and lower-sloping surfaces. When the grooves are small relative to the outer-solid radius the system provides a model for contactangle hysteresis due to surface roughness. An observed contact angle as a function of solid displacement gives a hysteresis loop for a chosen intrinsic contact angle.