Dynamic squeezing of liquid bridge between two spherical particle surfaces

Liquid bridges, as essential capillary phenomena, provide critical theoretical foundations for understanding wet granular materials. Previous studies on liquid bridges have focused on static force analysis and stretching test; however, these findings cannot be reasonably applied to the evolution of capillary forces in wet granular materials under compression. This study aims to deepen the understanding of solid-liquid interaction mechanisms and provide insights for developing mechanical models of liquid bridges under squeezing.

Ethylene glycol was chosen as the experimental medium to minimize the evaporation effects. A liquid bridge force testing system was used to conduct alternating dynamic squeezing and static equilibrium experiments on the liquid bridge formed between two spherical particles. Image processing techniques were employed to determine the geometric parameters of the liquid bridge accurately. The temporal evolution characteristics of the liquid bridge morphology and the liquid bridge force (F_liq) were systematically analyzed.

Owing to contact angle hysteresis, a distinct three-stage evolution of geometric parameters was observed in quasi-static liquid bridges as the separation distance decreased. Under dynamic squeezing, viscous forces became the dominant interfacial force, exhibiting a greater dynamic variation than capillary forces, leading to a significant reduction in F_liq. During equilibrium, F_liq displayed a two-stage growth pattern: a rapid initial increase followed by a slower increase, eventually stabilizing within a range higher than the force before squeezing. Notably, the magnitude of the F_liq variation is governed by the extent of the geometric parameter changes induced by squeezing.