![]() Three drops/suspending fluid combinations were used and three types of substrates were studied, as detailed in Table 1. We used a microinterferometric technique, Reflection Interference Contrast Microscopy or RICM 23– 26 (see Supplementary Note 1 for details), capable of resolving film thicknesses down to a few nanometers 27, to study the drainage dynamics of the film of suspending fluid formed between the drop and the flat substrate. In our experiments, a drop with radius R ranging from 30 to 250 μm was introduced into an immiscible, suspending medium and allowed to settle under gravity toward a flat substrate. ![]() To achieve this, we employed polymer melts (silicone oils) as the suspending medium for the majority of our experiments, due to their high bulk viscosities and the enhanced viscosities of polymer films 13– 22 immobilized near surfaces (Fig. To examine the drainage and wetting stages more carefully, these processes need to be slowed down significantly to allow the capture of their mechanistic details. In this paper, we present evidence of a new mechanism of the wetting of a surface by an emulsion drop, which proceeds by the diffusion-mediated nucleation and growth of the drop phase on the substrate, and the eventual merging of a nucleated site with the parent drop (Fig. d A sketch of the adsorption and layering of polymer chains over molecular length scales near a substrate, inspired by past experiments and simulations 13– 22. The islands are much smaller than the parent drop, and the aspect ratio depends on the island contact angle. Note that the schematic shown is not drawn to scale. ![]() Here, a bridge between the approaching drop and one of the growing islands leads to the dewetting of the film of suspending medium, as shown in the magnified portion of the contact zone in the right panels. c The new mechanism observed in our experiments shows an alternative route, whereby diffusion of the dissolved drop fluid through the film causes nucleation and growth of islands of the drop fluid on the surface. The right panel of subfigures shows a magnified version of the contact zone. ![]() b Classical spinodal dewetting theory, which involves the formation of a bridge of diameter of the order of the film thickness between the wetting phase and the substrate, followed by the growth of the bridge and subsequent film rupture. For a drop settling down under its own weight, the net downward force is F = ( 4 / 3 ) π R 3 Δ ρ g, Δ ρ being the density difference between the drop and suspending phase, and g being the acceleration due to gravity. λ is the ratio of the viscosities of the drop and the suspending phases. R f is the radius of the contact zone formed due to the trapping of a film of the suspending phase between the drop and the surface. σ is the interfacial tension between the drop and suspending liquids. The Bond number Bo = Δ ρ g R 2 / σ is the dimensionless number characterizing the gravitational force relative to the interfacial force acting on the drop. The dynamics of droplet-surface interactions in the presence of an intervening film of the suspending medium.Ī Definition sketch of the film drainage process of one liquid in the approach of the drop of a second liquid toward a rigid, stationary surface.
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