Lateral and Normal Capillary Force Evolution of a Reciprocating Liquid Bridge

Abstract

Capillary forces of a shearing liquid bridge can significantly affect the friction and adhesion of interacting surfaces, but the underlying mechanisms remain unclear. We custom built a surface force apparatus (SFA, ±2 μN) equipped with in situ optical microscopy and performed normal and lateral force measurements on a reciprocating water bridge formed between two flat plates. A modified wedge method was developed to correct the unique force measurement errors caused by the changing bridge geometry and position. The results found (1) strong linear relations among the bridge shear displacement, the cosine difference between the left and right contact angles, and the lateral adhesion force and (2) the normal adhesion force increased monotonically up to 13% as the bridge geometry approached its axisymmetric state. Quasi-static force analyses based on a newly developed decahedral model showed good agreement with the experiments and improved accuracy compared with that of cylindrical or rectangular column models previously proposed in the literature. Although limited in certain aspects, this study may (1) prove helpful to the design and analysis of liquid bridge force experiments on platforms similar to the SFA used in this study and (2) help to bridge the gap between friction and liquid bridge physics in the literature.

The behavior of capillary suspensions at diverse length scales: From single capillary bridges to bulk

“…The advancing contact angle is always higher than the receding angle. For a bridge between two parallel plates, shearing the bridge in the lateral direction also decreases the normal capillary force, as it is maximal when the bridge is in its axisymmetric position and the cosine difference between the contact angles at the left and right contact point is minimal [54].…”

Advances in the Fabrication and Characterization of Superhydrophobic Surfaces Inspired by the Lotus Leaf

“…Several techniques have been developed or adapted to measure the adhesion, snap-in, pull-off, and friction forces of liquid drops on surfaces such as the use of tribometers [ 198 , 199 , 200 ], the surface forces apparatus (SFA) [ 201 , 202 ], atomic force microscopy [ 148 , 203 ], the centrifugal adhesion balance (CAB) [ 204 , 205 , 206 ], and microbalances including micro-electromechanical, micro-electrochemical, and microelectronics [ 107 , 207 , 208 , 209 , 210 , 211 , 212 , 213 , 214 , 215 ]. A Taylor–Couette cell has also been used to measure drag [ 216 ].…”

Hysteretic Behavior of Capillary Bridges between Flat Plates

“…This force was the unbalanced contact line force per unit length that arose from a contact angle different from Young’s equilibrium contact angle. Researchers have adapted this idea to model shearing bridges between flat plates using multibody dissipative particle dynamics simulations, surface energy minimization, lattice Boltzmann simulations, and experiments. , Similarly, it has successfully been used to model the tangential force arising from sliding drops. – In both cases, the advancing and receding contact angles have been included in the tangential force equations. However, there is still a need to investigate the link between contact angle hysteresis and tangential forces for capillary bridges with changing heights.…”

“…17 between flat plates using multibody dissipative particle dynamics simulations, 18 surface energy minimization, 19 lattice Boltzmann simulations, 20 and experiments. 19,21 Similarly, it has successfully been used to model the tangential force arising from sliding drops. 22−26 In both cases, the advancing and receding contact angles have been included in the tangential force equations.…”