Electro-wetting induced dynamic manipulation of symmetrically coalescing viscoelastic liquid bridges

Abstract

Merging of isolated liquid drops is a common phenomenon that may greatly be influenced by adding polymeric contents to the liquid. Here, we bring out an exclusive control on the dynamics of the intermediate liquid bridge, thus, formed via exploiting the interactions of an exciting electric field with a trace amount of polymeric inclusions present in the intermingling drops. Our results unveil a unique competition of the elastic recovery and time-oscillatory forcing during the drop-unification at early times. However, damped oscillations as a specific signature of the polymer concentration feature eventual stabilization of the bridge at later instants of time. We rationalize these experimental findings in light of a simple unified theory that holds its critical implications in droplet manipulation in a wide variety of applications encompassing digital microfluidics, chemical processing, and biomedical analytics.

Droplet-on-chip electro-spectroscopy detects the ultra-short relaxation time of a dilute polymer solution

“…2d), before attaining the eventual stable state. This could be explained by the fact that the droplet response time, defined as the time required by the droplet to achieve its maximum spreading 33 (corresponds to the minimum height), turned out to be a monotonically decaying function of the actuating frequency for f < f c (see Fig. 2a), beyond which the same saturated asymptotically to different limits as solely dictated by the PEG concentration, emphasizing the fact that the resulting features of damped oscillation were more predominantly governed by the fluid rheology rather than the frequency of the electrical pulsation.…”