Adjustable Capillary Forces Through Wetting State Changes in Liquid Bridges: Regulation via Trapezoidal Microstructures

A detailed understanding of the mechanistic role of solid surface microstructures in modulating capillary forces and liquid transport in liquid bridge systems is crucial, for liquid bridges between rough surfaces are omnipresent in nature and various industries. In this work, Gibbs free energy expression was derived for a liquid bridge system confined between a smooth surface and a microstructured surface, based on the principle of minimum thermodynamic potential. Furthermore, by analyzing the energy conversion during spacing variation between the two solid surfaces, an analytical expression for the capillary force of the liquid bridge was derived that incorporates the geometric parameters of the microstructures and the contact angle. Finally, numerical simulations were performed using the Fluent UDFs (User-Defined Functions) to validate the proposed capillary force model. The simulation results validated the analytical expression and revealed the influence of the microstructures on the force distribution on the upper and lower surfaces of the liquid bridge, and on the droplet transport performance.