Dynamic contact angle hysteresis in liquid bridges

TL;DR

This study combines experiments and theory to analyze how dynamic contact angle hysteresis in liquid bridges varies with loading rates, proposing power-law models and a predictive framework for capillary forces during cyclic deformation.

Contribution

It introduces a unified power-law correlation for dynamic contact angles across different liquids and develops a model capturing hysteresis effects under cyclic loading.

Findings

Hysteresis increases with higher loading rates.

Power-law correlations describe the relationship between contact angle and capillary number.

A predictive model accurately captures capillary force variations during cyclic loading.

Abstract

This work presents a combined experimental and theoretical study of dynamic contact angle hysteresis using liquid bridges under cyclic compression and stretching between two identical plates. Under various loading rates, contact angle hysteresis for three different liquids was measured by examination of advancing and receding angles in liquid bridges, and the capillary forces were recorded. It is found that, for a given liquid, the hysteretic phenomenon of the contact angle is more pronounced at higher loading rates. By unifying the behaviour of the three liquids, power-law correlations were proposed to describe the relationship between the dynamic contact angle and the capillary number for advancing and receding cases. It is found that the exponents of obtained power-law correlations differ from those derived through earlier methods (e.g., capillary rise), due to the different kinematics of the triple-line. The various hysteretic loops of capillary force in liquid bridges under varied cyclic loading rates were also observed, which can be captured quantitatively by the prediction of our developed model incorporating the dynamic contact angle hysteresis. These results illustrate the importance of varying triple-line geometries during dynamic wetting and dewetting processes, and warrant an improved modelling approach for higher level phenomena involving these processes, e.g., multiphase flow in porous media and liquid transfer between surfaces with moving contact lines.