The Effect of Surface Wettability on Viscoelastic Droplet Dynamics under Electric Fields

Abstract

The effects of surface wettability and viscoelasticity on the dynamics of liquid droplets under an electric field are studied experimentally. A needle-plate electrode system is used as the power source to polarize a dielectric plate by the corona discharge emitted at the needle electrode, creating a new type of steerable electric field realized. The dynamics of droplets between the dielectric plate and a conductive substrate include three different phenomena: equilibrium to a stationary shape on substrates with higher wettability, deformation to form a bridge between the top acrylic plate and take-off on the substrates with lower wettability. Viscoelastic droplets differ from water in the liquid bridge and takeoff phenomena in that thin liquid filaments appear in viscoelastic droplets, not observed for Newtonian droplets. The equilibrated droplet exhibits more pronounced heights for Newtonian droplets compared to viscoelastic droplets, with a decrease in height with the increase in the concentration of the elastic constituent in the aqueous solution. In the take-off phenomenon, the time required for the droplet to contact the upper plate decreases with the concentration of the elastic constituent increases. It is also found that the critical voltage required for the take-off phenomenon to occur decreases as the elasticity increases.

Chemical and Process Engineering

“…However, a "bead-ona-string" effect is observed, which stabilizes the process and reduces the number of potential secondary drops on primary drop breakup (Davidson et al, 2006;Tirtaatmadja et al, 2006). Other parameters which influence the process, especially in the presence of an electric field, include wettability and surface tension (He et al, 2017;Wei and Joo, 2022). These aspects of the droplet generation process, especially in terms of CFD simulations, will be studied in future work.…”

Editorial for the Special Issue on Micromachines for Non-Newtonian Microfluidics

“…Compared with Newtonian fluid, the Janus droplet is more readily generated in shear-thinning fluid. In the experimental study on the dynamics of liquid droplets under an electric field, Wei et al [5] observe that viscoelastic droplets differ from Newtonian droplets, and further discuss the effects of viscoelasticity, the wettability, and the droplet size.…”