Decrease in adhesion force at silica-mica interface with short contact time due to dynamic formation process of liquid bridge revealed on an AFM

Abstract

ABSTRACT The influence of instrumental parameters of an atomic force microscope (AFM) on adhesion forces demands clarification. Adhesion forces between a tipless cantilever and mica were measured in a humid environment to investigate the influence of instrumental parameters. The adhesion force measured repeatedly at a location is relatively stable with excellent reproducibility. The force abnormally decreases by ~10% with dwell time (0 ~ 0.4 s), then remains almost stable (0.4 ~ 10 s). The reason was the dynamic formation process of a liquid bridge. Due to a large driving pressure, the volume of the liquid bridge can increase intensely to the maximum one, which is larger than that in saturation. This leads to the reduction in the bridge by liquid flow, eventually resulting in the decrease. The force increases by a small magnitude with approach velocity and then remains stable. However, it increases logarithmically with retraction velocity and increases with piezo velocity with a concave downward shape in the logarithmic coordinate. The velocity dependence was ascribed to the dynamic enhancement of viscous force and the contact time dependence. The outcomes may help to understand the influence of instrumental parameters, and deepen the understanding of the formation mechanism of a liquid bridge.