Electrohydrodynamics of stationary mesoscale droplets for applications in fluid properties measurement and lab-on-chip devices

Abstract

Current fluid properties testing methods are bulky and property specific. They can be improved by implementing an all-in-one integrated lab on a chip device, that employs the principles of electrohydrodynamics. Current approaches of using droplet electrohydrodynamics for fluid properties testing are reviewed, providing a proof of concept for our proposed multiproperty sensing integrated device. Current approaches of mathematical modeling and simulations are also reviewed, providing a template to design our own simulations. Using syringe needles, a pair of mesoscale droplets are actuated using DC voltage for droplet electrocoalescence and varying AC voltage frequencies for droplet oscillations. Simulations for droplet electrocoalescence were also performed using COMSOLTM MultiPhysics® 5.4 simulation software, and the results validated against experimental data. The following droplet electrocoalescence phenomena were investigated with the aid of experiment and simulation data: coalescence time, critical conditions for coalescence, droplet bridge growth, and progression of electric field strength. The following droplet oscillations phenomena were investigated with the aid of experiment data: droplet deformation hysteresis plots for low AC voltage frequency operation, and frequency response of different fluids under AC voltage actuation. It is found that there is a non-linear relationship between applied electric field and coalescence time for droplets of various sizes. Furthermore, at low applied AC voltage frequency, droplet oscillation behavior is quasistatic, at resonant frequency, droplet displacement amplitude is very high, and at frequencies above resonant frequency, displacement amplitude reduces, and a phase lag is introduced.