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Enhancement of reaction rate in small-sized droplets: A combined analytical and simulation study

Mondal, Sayantan and Acharya, Subhajit and Biswas, Rajib and Bagchi, Biman and Zare, Richard N (2018) Enhancement of reaction rate in small-sized droplets: A combined analytical and simulation study. In: JOURNAL OF CHEMICAL PHYSICS, 148 (24).

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Official URL: https://dx.doi.org/10.1063/1.5030114

Abstract

Several recent mass spectrometry experiments reveal a marked enhancement of the reaction rate of organic reactions in microdroplets. This enhancement has been tentatively attributed to the accumulation of excess charge on a surface, which in turn can give rise to a lowering of activation energy of the reaction. Here we model the reactions in droplets as a three-step process: (i) diffusion of a reactant from the core of the droplet to the surface, (ii) search by diffusion of the reactant on the surface to find a reactive partner, and finally (iii) the intrinsic reaction leading to bond breaking and product formation. We obtain analytic expressions for the mean search time (MST) to find a target located on the surface by a reactant in both two-and three-dimensional droplets. Analytical results show quantitative agreement with Brownian dynamics simulations. We find, as also reported earlier, that the MST varies as R-2/D, where R is the radius of the droplet and D is the diffusion constant of the molecules in the droplet medium. We also find that a hydronium ion in the vicinity can substantially weaken the bond and hence lowers the activation barrier. We observe a similar facilitation of bond breaking in the presence of a static dipolar electric field along any of the three Cartesian axes. If the intrinsic reaction is faster compared to the mean search time involved, it becomes primarily a diffusion-controlled process; otherwise the reaction cannot be accelerated in the droplet medium. The air-droplet interface provides a different environment compared to the interior of the droplet. Hence, we might also expect a completely different mechanism and products in the case of droplet reactions. Published by AIP Publishing.

Item Type: Journal Article
Additional Information: Copyright of this article belong to AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Department/Centre: Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Depositing User: Id for Latest eprints
Date Deposited: 25 Jul 2018 15:28
Last Modified: 25 Jul 2018 15:28
URI: http://eprints.iisc.ac.in/id/eprint/60292

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