Contact angle measurement using a Hele-Shaw cell: A proof-of-concept study

Contact angle is an important property to quantify the wettability of a solid surface with a liquid, which characterizes interactions of the solid-liquid pair. Generally, to measure contact angle, special instruments such as a goniometer are necessary, but they are not readily available in certain research settings. In this study, an alternative method to measure contact angle based on a Hele-Shaw cell, microscopy imaging, and image processing is suggested. In this method, a liquid drop is injected into a transparent Hele-Shaw cell, the meniscus of the drop is captured in the top or bottom view using a brightfield microscope, and the contact angle is measured from the captured image based on a geometrical model of the drop in the Hele-Shaw cell. The proposed method was tested using two different liquids (deionized water and glycerol) and two different solid surfaces (polydimethylsiloxane [PDMS] and commercial water-repellent-coated glass) with various gap heights of Hele-Shaw cells and validated in comparison with a goniometer. Our results show that the proposed method could measure contact angles reasonably well. Although the concept of the proposed quick-and-dirty contact angle measurement method was proven in this study, there is still room to improve the accuracy and reliability of the proposed method.