Abstract
The objective of this research is to clarify the condensation process of water droplets on nanostructured surfaces by means of the sequential visualization of droplets using an environmental scanning electron microscope (ESEM). So far, we observed the condensation process of submicron-scale droplets on silicon (100) surface, where the contact angle of millimeter-sized droplets is around 60°-70°. During visualization measurements, the pressure of water vapor inside the ESEM chamber and the temperature of the sample stage were 700 Pa and 1.2 ℃, respectively. We found that the condensation growth of a submicron-sized droplet is classified into two modes. In the first mode, the contact angle of individual droplets is smaller than the macroscopic contact angle (600-700), which is the contact angle observed for millimeter-sized droplets, and increases linearly with time until reaching the macroscopic contact angle. In the second mode, which starts after the contact angle reaches the macroscopic contact angle, the base diameter increases with time while the contact angle remains constant.
