Rheocoalescence: Relaxation Time through Coalescence of Droplets

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* < c(e)/c*, viscoelastic c(e)/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 t(b), 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.

Automated summary

This study investigates the formation and development of neck droplets during coalescence using high-speed imaging. Based on the concentration ratio, three different regimes are identified, and it is found that the growth of the neck droplet radius follows different power-law behavior. A new measurement technique is proposed based on the dependence of the power-law exponent on concentration ratios, which can potentially predict the relaxation time of fluids in the elasticity dominated regime.