Abstract
Several researchers reported that the apparent contact angle increased with decreasing the contact line velocity when the apparent contact angle was measured from the spreading front of a liquid droplet colliding with flat surfaces at room temperature. The purpose of the present study is to discuss the reason why such an experimental result, which is against the well-know fact, was obtained. A mathematical model describing the fluid dynamics during the droplet impingement on a flat surface is numerically solved to investigate the configuration of the droplet frame near the contact line. As a result, the complicated configuration in the initial stage causes measurement errors on the apparent contact angle.
