濡れ性の異なる円板に付着した液滴の回転加速中における動的濡れ性に関する研究

抄録

Liquid droplets adhered to a rotating disk will deform by the centrifugal force and then detach from the surface when the centrifugal force exceeds the critical force. Previous studies about the onset motions of droplets were conducted at the constant rotational speed of the disk. In this study, the deformation process of the droplets until sliding is investigated at various wettability and angular acceleration α = 50, 150 rpm/s by using a high-speed camera. The droplets of aqueous ethanol solutions are placed on substrates with various wettability. The droplets volume are V = 5, 10 μL. It is shown that the deformation and sliding processes of the droplets could be roughly classified into two types, which the droplet before sliding has a trail or not. However, there are droplets that cannot be classified into the two types. Those droplets are sometimes, but not always, trailing even under the same conditions. For classified droplets, the critical sliding contact angles depend on the initial contact angle, and the approximate equations for critical contact angles are shown as function of initial contact angle at each type. The Furmidge equation for critical sliding force on an inclined plate is found to be valid for droplets on a rotating disk. Therefore, if the deformation process before sliding can be classified, the sliding critical force can be predicted from the static parameters, which are the initial contact angle and the initial droplet length (Diameter of droplet).