Coalescence of polymeric sessile drops on a partially wettable substrate

Abstract

Coalescence of sessile polymeric fluid drops on a partially wettable substrate exhibits a transition from the inertial to viscoelastic regime at concentration ratio c=c à $ 1. Our findings unveil that the temporal evolution of the growing bridge height follows a power law behavior t b , such that the coefficient b continuously decreases from 2/3 in the inertial regime (c=c à < 1) to an asymptotic value of 1/2 in the viscoelastic regime (c=c à > 1Þ. To account for fluid elasticity and characteristic timescale in the viscoelastic regime, a modified thin film equation under lubrication approximation has been proposed using the linear Phan-Thien-Tanner constitutive equation. The temporal evolution of the droplet has been evaluated by solving the modified one-dimensional thin film equation using a marching explicit scheme. The initial droplet shapes are obtained by resorting to energy minimization. Good agreement between numerical and experimental results is obtained.

Rheocoalescence: Relaxation Time through Coalescence of Droplets

“…This temporal growth bears the signature of the underlying governing equation . Such natural processes are observed in raindrop condensation , and industrial processes such as paint spray coatings, , combustion process, droplets on surfaces, and processes linked to life. , Depending on the relative orientation of droplets, the phenomenon can occur in physically different configurations, i.e., pendant–pendant, − sessile–pendant, and sessile–sessile. − The entire evolution process in pendant–pendant and sessile–pendant configurations is driven by a balance between surface tension, viscous and inertial effects, and Laplace pressure. , In Newtonian fluids, based on the force balance, the evolution lies in either the inertia dominated or viscosity dominated regime. , Apart from these regimes, a new regime of inertially limited viscous regime was proposed in Newtonian droplet coalescence, wherein all inertial, viscous, and surface tension forces are essential.…”

“…Kinematic similarity is retained in all these phenomena, but the dynamic similarity is affected due to the addition of elastic forces. A recent study of aqueous solutions of polymer droplets on both pendant–sessile and sessile–sessile configurations emphasized the role of relaxation time on the dynamics of neck radius evolution. The former study of pendant–sessile configuration showed that for , where Wi = λ U / R (λ is relaxation time and U is neck velocity) is the Weissenberg number, the neck radius growth follows the scale of R ∼ t 0.36 .…”

Shock induced aerobreakup of a polymeric droplet

“…The value of critical overlap concentration, c * ≈ 0.06%w/w and relaxation times are estimated from the correlations available in the literature 29 . A wide range of c/c * variation (∼ 10…”

Numerical Study of the Coalescence and Mixing of Drops of Different Polymeric Materials

“…Coalescence of microscopic or macroscopic liquid drops has been one of the most widely researched multiphase problems owing to its significant role in a variety of phenomena like cloud formation and precipitation, oil spills, emulsions, additive manufacturing processes − such as aerosol jet printing, inkjet printing, syringe/extrusion printing, electrohydrodynamic (EHD) jet printing, etc. The effects of viscosity, surface tension, and surface wettability on the coalescence dynamics of Newtonian droplets on both solid surfaces and liquid films have been well studied. − Recently, a number of researchers have studied the coalescence dynamics of non-Newtonian polymeric droplets, − including the effect of impact velocity. The coalescence dynamics of the drops are usually quantified by studying the growth of the bridge connecting the drops.…”