• drop shape analysis
• dynamic contact angle
• stainless steel
• wetting

An experimental procedure to measure the contact angle of growing and shrinking of water drops on stainless steel is here presented. The volume of the drop is controlled with a syringe pump who injects and withdraws water through a capillary pierced directly on the surface tested. The pump works at different constant flow rates in the limit of low capillary numbers to neglect inertial effects. During the experiments the drop profile is recorded with a digital camera and the footage is processed with a MatLab script written for the purpose.
The script is able to automatically detect the edge of the drop and the contact line. The Laplace set of equations describing the profile of a liquid drop is fitted on the detected drop edge by iterative optimization of a geometric parameter and a physical parameter of the drop. From the fitted profile we are able to evaluate the contact angle of the drop and other needed parameters.
From the experiments the advancing and receding angles have been found dependent on time and in agreement with the literature. We expect that an asymptotic value of the advancing contact angle could be reached for very long injection times when the rate of expansion of the wet diameter in the unit of time tends to zero.