Abstract:
Common feature of μTAS is impact on a droplet on a microfluidic channel for functional analysis. It has been observed that both hydrophilic and hydrophobic nature has their usual applications but shifting of wetting mode is also important for μTAS. One such mode of wetting mode shifted is electrowetting. In the present study droplet impact using electrowetting has been studied numerically.
A coupled electro hydrodynamic model is used to explore the phenomenon of droplet impact on a charged surface. The spatio-temporal electric field is obtained from the solution to Poisson and charge conservation equation. The electrostatic forces are coupled with hydrodynamics by incorporation of Maxwell stress term of the two-phase momentum equation. Geometry of the foot print of the charged region is varied to control the contact line mobility. The electrical stress generated near the three phase contact-line due to the presence of electric field constrains its motion in the desired direction and causes a change of impact behavior. It can be observed that a hydrophilic surface shows hydrophobic characteristics when the droplet is collided with it at a concentric ring shaped charged regions. As the phenomenon is mainly governed by the interplay between electrostatic, capillary and inertia forces it is explored through the parametric variation of applied voltage as well as parametric variation of contact angle and impact height. It has been observed that the application of voltage can change hydrophilic surface into a bouncing hydrophobic one for application of μTAS. The outcome of the present study can be utilized to develop a vast range of engineering surfaces for various applications like drop wise condensation, anti-corrosion and self- cleaning and microfluidics.
