Static and dynamic contact angle measurements using a custom-made contact angle goniometer

Contact angle is a physical quantity used to evaluate the interaction between a solid surface and a liquid. However, many research laboratories or educational institutions with budget constraints have limited access to a commercial contact-angle goniometer with a high-resolution imaging system. In this study, we fabricated a custom-made contact angle goniometer with a smartphone and quantified the contact angles of water on various surfaces. We found that the receding contact angles on the surfaces were sensitive to the change in flow rates. The receding angle sharply decreases when the flow rate exceeds 50 µl/min, indicating that accurate flow control is required in contact angle measurements. The dynamic contact angles could also be quantified by the developed goniometer in an extremely low-capillary number regime. The dynamic advancing and receding contact angles on tested surfaces followed the molecular-kinetic theory.