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Dynamic measurements and simulations of airborne picolitre-droplet coalescence in holographic optical tweezers

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posted on 2016-11-02, 15:37 authored by Bryan R. Bzdek, Liam Collard, James E. Sprittles, Andrew J. Hudson, Jonathan P. Reid
We report studies of the coalescence of pairs of picolitre aerosol droplets manipulated with holographic optical tweezers, probing the shape relaxation dynamics following coalescence by simultaneously monitoring the intensity of elastic backscattered light (EBL) from the trapping laser beam (time resolution on the order of 100 ns) while recording high frame rate camera images (time resolution <10 μs). The goals of this work are to: resolve the dynamics of droplet coalescence in holographic optical traps; assign the origin of key features in the time-dependent EBL intensity; and validate the use of the EBL alone to precisely determine droplet surface tension and viscosity. For low viscosity droplets, two sequential processes are evident: binary coalescence first results from the overlap of the optical traps on the time scale of microseconds followed by the recapture of the composite droplet in an optical trap on the time scale of milliseconds. As droplet viscosity increases, the relaxation in droplet shape eventually occurs on the same time scale as recapture, resulting in a convoluted evolution of the EBL intensity that inhibits quantitative determination of the relaxation time scale. Droplet coalescence was simulated using a computational framework to validate both experimental approaches. The results indicate that time-dependent monitoring of droplet shape from the EBL intensity allows for robust determination of properties such as surface tension and viscosity. Finally, the potential of high frame rate imaging to examine the coalescence of dissimilar viscosity droplets is discussed.

History

Citation

Journal of Chemical Physics, 2016, 145 (5), 054502

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Chemistry

Version

  • VoR (Version of Record)

Published in

Journal of Chemical Physics

Publisher

AIP Publishing

issn

0021-9606

eissn

1089-7690

Acceptance date

2016-07-14

Copyright date

2016

Available date

2016-11-02

Publisher version

http://scitation.aip.org/content/aip/journal/jcp/145/5/10.1063/1.4959901

Language

en

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