A Simplified Approach for Dynamic Contact Angle Measurements

Contact angle measurement is a valuable tool for analyzing surface properties, including surface structure, cleanliness, and solid-liquid interactions. Typically, this measurement is performed at the static state, capturing the interactions at the solid-liquid interface when the gas, liquid, and solid phases reach equilibrium. In this study, we developed a user-friendly setup for accurately measuring dynamic contact angles using the needle-in-drop method. Our setup consists of a syringe for controlled liquid dispensing and withdrawal on a solid surface, a sample stage with a scale bar for baseline measurements (the diameter of the droplet), a lens to magnify the image of the droplet on the solid surface, and a smartphone camera for recording the dynamic expansion and retraction of the liquid droplet. In addition to obtaining the static sessile-drop contact angle information, our modified setup allows for the acquisition of other relevant parameters, including contact angle hysteresis and the contact-line pinning force. By training students to assemble a cost-effective contact angle measurement setup using laboratory components and guiding them in the utilization of this setup for conducting static and dynamic contact angle measurements, students gain practical experience to determine the surface wettability and interfacial energy from static contact angle measurements and to characterize the interfacial hysteresis and liquid mobility from dynamic contact angle measurements. We anticipate that this approach will benefit students in a wide range of disciplines, including materials science, chemical engineering, and physical chemistry, where understanding surface properties is essential.