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Micromachines 2016, 7(1), 13; doi:10.3390/mi7010013

Thermocapillarity in Microfluidics—A Review

Department of Mechanical and Aerospace Engineering, University of Central Florida, Orlando, FL 32816, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Jeong-Bong Lee
Received: 1 November 2015 / Revised: 1 January 2016 / Accepted: 8 January 2016 / Published: 21 January 2016
(This article belongs to the Collection Lab-on-a-Chip)

Abstract

This paper reviews the past and recent studies on thermocapillarity in relation to microfluidics. The role of thermocapillarity as the change of surface tension due to temperature gradient in developing Marangoni flow in liquid films and conclusively bubble and drop actuation is discussed. The thermocapillary-driven mass transfer (the so-called Benard-Marangoni effect) can be observed in liquid films, reservoirs, bubbles and droplets that are subject to the temperature gradient. Since the contribution of a surface tension-driven flow becomes more prominent when the scale becomes smaller as compared to a pressure-driven flow, microfluidic applications based on thermocapillary effect are gaining attentions recently. The effect of thermocapillarity on the flow pattern inside liquid films is the initial focus of this review. Analysis of the relation between evaporation and thermocapillary instability approves the effect of Marangoni flow on flow field inside the drop and its evaporation rate. The effect of thermocapillary on producing Marangoni flow inside drops and liquid films, leads to actuation of drops and bubbles due to the drag at the interface, mass conservation, and also gravity and buoyancy in vertical motion. This motion can happen inside microchannels with a closed multiphase medium, on the solid substrate as in solid/liquid interaction, or on top of a carrier liquid film in open microfluidic systems. Various thermocapillary-based microfluidic devices have been proposed and developed for different purposes such as actuation, sensing, trapping, sorting, mixing, chemical reaction, and biological assays throughout the years. A list of the thermocapillary based microfluidic devices along with their characteristics, configurations, limitations, and improvements are presented in this review. View Full-Text
Keywords: thermocapillary; microfluidic; actuation; MEMS devices; evaporation; instability; droplet; bubble thermocapillary; microfluidic; actuation; MEMS devices; evaporation; instability; droplet; bubble
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Karbalaei, A.; Kumar, R.; Cho, H.J. Thermocapillarity in Microfluidics—A Review. Micromachines 2016, 7, 13.

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