Rheocoalescence: Relaxation Time through Coalescence of Droplets
Sarath Chandra Varma, Abhineet Singh Rajput, Aloke Kumar
Abstract
The dynamics of the pendant drop coalescing with a sessile drop to form a single daughter droplet is known to form a bridge. The bridge evolution begins with a point contact between the two drops leading to a liquid neck of size comparable to the diameter of the drops. To probe this phenomenon in polymeric fluids, we quantify the neck radius growth during coalescence using high-speed imaging. In this study, we unveil the existence of three regimes on the basis of concentration ratio c/c*, namely, inertioelastic c/c* < ce/c*, viscoelastic ce/c* < c/c* < 20, and elasticity dominated regimes c/c* > 20. Our results suggest that the neck radius growth with time (t) obeys a power-law behavior tb, such that the coefficient b has a steady value in inertioelastic and viscoelastic regimes, with a monotonic decrease in elasticity dominated regime. On the basis of this dependence of b on concentration ratios, we propose a new measurement technique, rheocoalescence, which possibly can predict the relaxation time of these fluids in the elasticity dominated regime. We also show a deviation from universality proposed in the literature for the elasticity dominated regime.