Marangoni spreading due to a localized alcohol supply on a thin water film

Abstract

Bringing two miscible fluids into contact naturally generates strong gradients in surface tension. Here, we investigate such a Marangoni-driven flow by continuously supplying isopropyl alcohol (IPA) on a film of water, using micron-sized droplets of IPA-water mixtures. These droplets create a localized depression in surface tension that leads to the opening of a circular, thin region in the water film. At the edge of the thin region, there is a growing rim that collects the water of the film, reminiscent of Marangoni spreading due to locally deposited surfactants. In contrast to the surfactant case, the driving by IPA-water drops gives rise to a dynamics of the thin zone that is independent of the initial layer thickness. The radius grows as r ∼ t 1/2 , which can be explained from a balance between Marangoni and viscous stresses. We derive a scaling law that accurately predicts the influence of the IPA flux as well as the thickness of the thin film at the interior of the spreading front. C 2015 AIP Publishing LLC. [http://dx.

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“…Examples of anti-surfactants include many salts, such as sodium chloride, i.e. common table salt, when added to water [19,18], water when added to short-chain alcohols [11], and certain resins that are included in solvent-based paints [29,12]. Here, we consider the Riemann problem for a thin film of a perfectly soluble anti-surfactant solution [6] in the limit of large capillary and Péclet numbers and the solution of which belongs to some measure space…”

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“…In this work, we study the influence of a volatile solvent on the evolution of a thin liquid film on a solid surface. As the volatile solvent diffuses through the atmosphere, a non-uniform solvent concentration arises which induces surface tension gradient and Marangoni-driven flow [1][2][3]. This effect is well-known and was described in the pioneering works of Marangoni [4] and Thomson [5].…”

Simple waves and shocks in a thin film of a perfectly soluble anti-surfactant solution

“…The system of nonlinear equations given by (6) and (7) is purely hyperbolic, and so may be written in characteristic form with Riemann invariants r ± = hb ±1 , which are constant along the characteristic curves in the (x, t)-plane with slopes given by the eigenvalues…”

“…Examples of anti-surfactants include many salts, such as sodium chloride, i.e. common table salt, when added to water [1][2][3][4], water when added to short-chain alcohols [5,6], and certain resins that are included in solvent-based paints [7][8][9][10].…”