Effects of the surface tension gradient and viscosity on coalescence-induced droplet jumping on superamphiphobic surfaces

Abstract

With the development of superhydrophobic surface preparation technology, coalescence-induced droplet jumping shows broad application prospects in the fields of enhanced condensation heat transfer and self-cleaning. In this work, the coalescence-induced jumping process of heterogeneous and homogeneous droplets on superamphiphobic surfaces was studied by using glycerol–water mixtures with different glycerol volume fractions. The results showed that the surface tension gradient of heterogeneous droplets will lead to asymmetric deformation of droplets, asymmetric distribution of internal pressure of droplets, as well as decrease in the energy conversion efficiency and the vertical departure velocity. Our study also revealed that the effects of surface tension gradient and viscosity on droplet jumping are different in the two regions. When the glycerol volume fraction is less than 40%, the droplet velocity and energy conversion are dominated by the surface tension gradient, and the vertical departure velocity and the energy conversion efficiency of homogeneous droplets are larger. When the glycerol volume fraction is greater than 40%, the droplet velocity and energy conversion are dominated by the surface tension gradient and viscosity together, and the vertical departure velocity and the energy conversion efficiency of heterogeneous droplets are larger.

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

“…The values of θ 1, eq = θ PVAc, eq and θ 2, eq = θ PMMA, eq have been obtained from the literature (refs , and have been provided in Table . A few studies have shown such linear variation of the contact angle with the volume fraction of the species. − In the absence of measurement of the exact variation of the contact angle, which the PMMA/PVAc blend (or mixture) makes with the substrate, with the volume fraction of the individual polymeric material (PMMA or PVAc), such a linear variation assumption has been incorporated.…”

Optimum substrate stiffness in coalescence-induced droplet jumping

“…Successful jumping relies largely on overcoming the adhesion between the surface and the droplet, which is closely related to wettability. Another factor that affects the efficiency of energy conversion is the internal viscous dissipation of the droplet, 29,30 which slows down the expansion of the liquid bridge that impacts the surface. The Ohnesorge number Oh ¼ m= ffiffiffiffiffiffiffiffiffi rsR p is used to describe the properties of the droplet, where m is the viscosity, r is the density of the liquid, s is the surface tension, and R is the radius of the droplet.…”

Coalescence-induced jumping of droplets from superhydrophobic surfaces—The effect of contact-angle hysteresis

“…Jumping of droplets on superhydrophobic surfaces has also been investigated numerically. From the realm of continuum-based techniques that focus on capturing or tracking the interface, volume of fluid (VOF) was mostly selected 33,42,43,45,[47][48][49][50][51] even though several other methods were also used. 44,[52][53][54] In addition, there are studies using either a lattice Boltzmann framework [40][41][42][55][56][57] or molecular dynamics [57][58][59] with results that in principle showed the same trends and observations as did the experiments and continuum-based simulations.…”