Lateral and Normal Capillary Force Evolution of a Reciprocating Liquid Bridge

Area of Science:

• Surface science
• Fluid mechanics
• Tribology

Background:

• Capillary forces from liquid bridges are crucial for surface friction and adhesion.
• The precise mechanisms governing these forces remain incompletely understood.

Purpose of the Study:

• To investigate the relationship between liquid bridge geometry and capillary forces.
• To quantify the impact of shearing liquid bridges on normal and lateral adhesion forces.
• To develop accurate models for predicting liquid bridge forces.

Main Methods:

• Custom-built surface force apparatus (SFA) with in situ optical microscopy for force measurements.
• Development of a modified wedge method to correct for measurement errors due to changing bridge geometry.
• Quasi-static force analyses using a novel decahedral model.

Main Results:

• Identified strong linear correlations between bridge shear displacement, contact angle differences, and lateral adhesion force.
• Observed a monotonic increase in normal adhesion force (up to 13%) as the liquid bridge approached an axisymmetric state.
• The decahedral model demonstrated superior accuracy in predicting forces compared to existing cylindrical or rectangular models.

Conclusions:

• The findings provide a quantitative understanding of liquid bridge forces in shearing conditions.
• The developed methods and models can aid in the design and analysis of similar surface force experiments.
• This research contributes to bridging the gap between friction science and liquid bridge physics.