Kinetics of liquid annulus formation and capillary forces.

The dependence of the capillary adhesion force Fcap between a silica microsphere and a flat silica surface versus a time period t of the samples’ contact (i.e., dwell-in time) is experimentally investigated using atomic force microscopy (AFM). Fcap was found to be dependent on t if the humidity was >30–35%. This dependence is exponential, with decay (characteristic) times of ∼10 s. It is suggested that the kinetics of the adhesion process are related to the growth of the water annulus between surfaces. Furthermore, we propose that the growth kinetics has two components: (1) water vapor diffusion from the surrounding humid media into the gap between samples and (2) water drainage from the gap. The theory of diffusion through thin pores (i.e., gaps) is developed, and analytical formulas are obtained for the dependence of the meniscus radius r versus time t. However, the experimental dependence of Fcap versus t and, consequently, r versus t obtained in this article disagrees with the theoretical prediction b...