Symmetric and asymmetric coalescence of droplets on a solid surface in the inertia-dominated regime

Abstract

We present an investigation of symmetric and asymmetric coalescence of two droplets of equal and unequal size on a solid surface in the inertia-dominated regime. Asymmetric coalescence can result due to the coalescence of two unequal-sized droplets or coalescence of two droplets having different contact angles with the surface due to a step gradient in wettability. Based on the solution of an analytical model and lattice Boltzmann simulations, we analyze symmetric and asymmetric coalescence of two droplets on a solid surface. The analysis of coalescence of identical droplets show that the liquid bridge height grows with time as (t*)1/2 for θ = 90° and (t*)2/3 for θ < 90°, where t* is dimensionless time. Our analysis also yields the same scaling law for the coalescence of two unequal-sized droplets on a surface with homogeneous wettability. We also discuss the coalescence of two droplets having different contact angles with the surface due to a step gradient in wettability. We show that the prediction of bridge height with time scales as (t*)2/3 irrespective of contact angles of droplet with the surface.

Self similarity of liquid droplet coalescence in a quasi-2D free-standing liquid-crystal film

“…Droplets attached to flat solid substrates show a qualitatively different dynamics of merging, mainly because the flow field is qualitatively different from that in the coalescence of free droplets, owing to no-slip conditions for the flow field at the solid surface [29][30][31][32][33][34][35][36][37][38] . The wetting characteristics of the fluid on the substrate is relevant and the contact angle becomes an important parameter.…”

Coalescence of nematic liquid crystal droplets on freely suspended liquid crystal films

“…The parameter A and b can be determined from the experiment. The power b has been of significant interest [4][5][6][7][8][9][10][11][12][13]15] in the study of diffusion and coalescence of liquid interface. The event in the plot of figure 6 for both experiment and simulation yielded the result shown in table 1.…”

“…Freely suspended liquid crystal film can be prepared with a film thickness ranging from two to a few hundred molecular layers. Various experiments have been performed on coalescence of smectic islands in thin smectic liquid crystal films [3][4], including observations of droplet coalescence on smectic films and other types of droplets that perform similar combination behaviour to the coalescence of islands on smectic films surface, and simulating the coalescence of droplets using scaling law [4][5][6][7][8][9][10].…”

Swalbe.jl: A lattice Boltzmann solver for thin film hydrodynamics

“…the exponent 𝛼 should be 2/3 (Pawar et al, 2019;Sui et al, 2013). This experiment has been performed using the Pluto notebook Drop_coal.jl.…”