研究成果

Communications: Wall free capillarity and pendant drop removal

Siang-Jie Hong, Feng-Ming Chang, Seong Heng Chan, Yu-Jane Sheng,* and Heng-Kwong Tsao*

When a sessile drop encounters a pendant drop through a hole, it is generally anticipated that they will coalesce and flow downward due to gravity. However, like “wall-free” capillarity, we show that the pendant drop may be sucked up by a sliding drop instantaneously if the radius of the curvature of the former is smaller than that of the later. This phenomenon can be explained by Laplace–Young equation and convective Ostwald ripening. Our results indicate that superhydrophilic perforated surface can be used as an effective way for the removal of small droplets adhering to the inner walls of microchannel systems.

The following movie illustrates a typical example of a smaller drop swallowing a larger one. Initially, a small drop with volume 0.4 μl sits on the superhydrophilic side. Beneath the hole, a large drop with volume 15.3 μl residing on the normal plane of acrylic glass moves upwardly. The upward flow process takes place immediately as the two drops meets.