Microscale tracking of unconstrained moving multiphase contact lines via a capacitance sensor array

• Published in: Sensors and actuators. A. Physical. 2021-11, Vol.331, p.113046, Article 113046
• Main Authors: Mondal, Md Tanbin Hasan, Desai, Tithi, Hossain, Rifat-E.-Nur, Moore, Arden L.
• Format: Article
• Language: English
• Subjects: Biological activity; Capacitance; Capacitance sensor array; Contact angle; Contact angle measurement; Droplets; Electrodes; Heat transfer; Interdigitated electrodes; Moving contact lines; Multiphase; Real time; Sensor arrays; Sensors; Studies; Tracking; Tracking control systems; Unconstrained droplet detection; Water drops
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2021.113046

•A novel sensor capable of tracking moving contact lines for unconstrained droplets.•Capacitance sensor array tracks bidirectional (advancing and receding) movement.•Multiphase contact line position and speed able to be measured and validated.•Rate of capacitance change scales with the advancing and receding contact angles. [Display omitted] The ability to track the spatial location of a moving multiphase contact line in time significantly enhances understanding into the fundamental physics behind biological processes, condensation- and evaporation-based heat transfer, and a host of other important phenomena. In this work, we present a capacitance-based microdevice capable of tracking a moving phase interface at the microscale for an unconstrained liquid droplet. The microdevice is comprised of an array of planar interdigitated electrodes beneath a thin insulating polymer layer. Monitoring changes in capacitance with time facilitates sensing of the multiphase contact line location and speed as it passes over each capacitance sensor in turn. This capacitive sensing scheme is designed to be highly sensitive and noninvasive to the droplet under study. Results show the speed and location of moving multiphase contact lines for advancing and receding water droplets are indeed able to be detected through the change in capacitance signals in the sensor array. It is also shown that the array can be used to measure the advancing and receding contact angles of unconstrained droplets.