Three stages of Marangoni-driven film spreading for miscible fluids

Abstract

The Marangoni-driven film spreading in the fully miscible droplet-reservoir system was experimentally studied. Three stages of film spreading were identified over a relatively long time, with the power-law exponent n ( R~ tn, R is film radius, t is time) nonmonotonically transitioning from 3/4, to 1/4, and back to 3/4. The variation of the Marangoni stress was found to be responsible for the three-stage power-law relationships, with the tangential stretching effect of the expanding liquid-air interface governing Stages I and III, and the normal diffusion effect dominating Stage II. This work presents a unified interpretation on the inconsistent power-law relationships reported from previous studies on Marangoni-driven film spreading for miscible fluids.

Unraveling the Surface Activity of Ethanol–Water Mixtures through Experiments and Molecular Dynamics Simulations

“…We analyzed the spreading behavior of ethanol droplets over pure water (0%) and solutions with 2.5, 5, 7.5, 10, 12.5, and 15% molar ethanol concentration X E in water. Similar to prior observations in the literature, 39,55 we note the following chain of events in our experiments (Figure 4a−h), where the ethanol concentration X E in the pool was <10%: the drop tries to spread soon after impingement (Figure 4a,e), however, instabilities kick in and destabilize the droplet perimeter (Figure 4b,f), which is further enhanced, and plumes and finger kinds of patterns can be readily seen (Figure 4c,g). These patterns and the spreading film are further destabilized (Figure 4d,4h), wherein the film ruptures at multiple locations forming holes.…”