electrowetting, numerical modeling, Young-Lippmann equation


A new method of characterizing electrowetting is presented in which the forces applied to a modified nanoindenter tip by a test water droplet are measured. A droplet is trapped between the flat nanoindenter tip and the test substrate containing the necessary electrodes. When voltage is applied to the electrodes in the substrate, lateral and normal forces are exerted on the tip and measured by the nanoindenter transducer. Proper selection of the tip geometry permits direct prediction of the resulting in-plane lateral forces using analytical formulas derived from the Young-Lippmann equation. Experimental results show good agreement with both analytical and numerical predictions. Numerical modeling using Surface Evolver shows that the lateral forces are relatively insensitive to most alignment errors. The analytical model is most accurate for small tip/substrate gaps. Evaporation of the test liquid can introduce modest errors in long measurements, but compensation methods are presented. The nanoindenter sensor provides microNewton force resolution with fast response time. As the droplet undergoes almost no movement, the fluid dynamics have minimal impact on the measured forces and transient electrowetting events are readily detected. Experimental results show significant response at frequencies up to 40 Hz. This setup is useful in measuring electrowetting responses at high speeds and in measuring system degradation processes.

Original Publication Citation

N. B. Crane, P. Mishra, and A. Volinsky, “Characterization of Electrowetting Processes through Force Measurements,” Review of Scientific Instruments, Vol 81, 2010, 043902.

Document Type

Peer-Reviewed Article

Publication Date



Review of Scientific Instruments




Ira A. Fulton College of Engineering and Technology


Mechanical Engineering

University Standing at Time of Publication

Full Professor