Liquid contact angle measurement based on photographing to measure the top height

A method is proposed to calculate the liquid–solid contact angle by photographing the liquid surface height inside a transparent capillary tube, which simplifies the steps of measuring the contact angle by eliminating the need to search for the three-phase contact points and omitting the process of fitting the function to the liquid surface contour. The relationship between the contact angle of a fixed volume of liquid and solid wall in a capillary tube and the height of the liquid surface vertex is deduced, and the liquid surface height is obtained by taking pictures and image processing to obtain the liquid contour inside the tube, which is then substituted into the relationship equation to obtain the liquid contact angle. Taking the experiment of the electric wetting effect as an example, the relationship curve consistent with the theoretical value was obtained, which verified the feasibility of the vertex height method.