Droplet Heating Using Liquid Dielectrophoresis: A Parametric Study

Abstract

Droplet manipulation using digital microfluidics is extensively being researched for various biological and chemical sensor applications. Among the various methods, liquid dielectrophoresis (L-DEP) offers precise droplet manipulation using high-frequency electric fields. L-DEP also aids in generating temperature inside the droplet. Even though droplet heating using L-DEP promises various potential capabilities in microfluidic sensor development, droplet actuation at high voltages [greater than 400 V peak voltage (V _p )] remains a concern. In this manuscript, the parameters, such as dielectric material and dielectric thickness, which are responsible for droplet heating, are investigated numerically through simulations. By keeping the dielectric thickness constant, the relation between temperature rise and frequency for various V _p was simulated for seven different dielectrics, mainly Si ₃ N ₄ , ZnO, and alumina. A temperature rise of 100 °C was generated using V _p = 200 V at 200 kHz using Si ₃ N ₄ as the dielectric, which proves the capability of using this technique at lower voltages. However, the complexity in fabrication hinders its usage in microfluidic applications. Thus, we investigated low dielectric strength materials, such as ZnO and alumina. We observed that despite the dielectric film being porous, due to synthesis, the effect of the porosity of these films in droplet heating is found to be minimal. Finally, the variation of temperature rise inside the droplet with varying dielectric film thickness for various kHz frequencies by keeping the V _p is studied. This study is crucial in developing droplet thermal sensors, which could replicate the functions of microheaters for various microfluidic applications.