Enhancement of mixing in a viscous, non-volatile droplet using a contact-free vapor-mediated interaction

Hegde, O and Kabi, P and Basu, S (2020) Enhancement of mixing in a viscous, non-volatile droplet using a contact-free vapor-mediated interaction. In: Physical Chemistry Chemical Physics, 22 (26). pp. 14570-14578.

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Abstract

Mixing at small fluidic length scales is especially challenging in viscous and non-volatile droplets frequently encountered in bio-chemical assays. In situ methods of mixing, which depend on diffusion or evaporation-driven capillary flow, are typically slow and inefficient, while thermal or electro-capillary methods that are either complicated to implement or may cause sample denaturing. This article demonstrates an enhanced mixing timescale in a sessile droplet of glycerol by simply introducing a droplet of ethanol in its near vicinity. The fast evaporation of ethanol introduces molecules in the proximity of the glycerol droplet, which are preferentially adsorbed (more on the side closer to ethanol) creating a gradient of surface tension driving the Marangoni convection in the droplet. We conclusively show that for the given volume of the droplet, the mixing time reduces by �10 hours due to the vapour-mediated Marangoni convection. Simple scaling arguments are used to predict the enhancement of the mixing timescale. Experimental evidence obtained from fluorescence imaging is used to quantify mixing and validate the analytical results. This is the first proof of concept of enhanced mixing in a viscous, sessile droplet using the vapour mediation technique. © the Owner Societies.

Item Type:	Journal Article
Publication:	Physical Chemistry Chemical Physics
Publisher:	Royal Society of Chemistry
Additional Information:	Copyright for this article belongs to Royal Society of Chemistry.
Keywords:	Drops; Ethanol; Evaporation; Fluorescence imaging; Glycerol; Heat convection, Analytical results; Capillary method; Experimental evidence; Gradient of surface tension; Marangoni convection; Mediated interaction; Proof of concept; Sessile droplet, Mixing
Department/Centre:	Division of Interdisciplinary Sciences > Interdisciplinary Centre for Energy Research Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	11 Nov 2021 11:51
Last Modified:	11 Nov 2021 11:51
URI:	http://eprints.iisc.ac.in/id/eprint/66091

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