Comment on "Patterns in Drying Drops Dictated by Curvature-Driven Particle Transport"

Chris S Hodges; S Mick Tangparitkul

doi:10.1021/acs.langmuir.9b01442

Comment on "Patterns in Drying Drops Dictated by Curvature-Driven Particle Transport"

Langmuir. 2019 Jul 30;35(30):9988-9990. doi: 10.1021/acs.langmuir.9b01442. Epub 2019 Jul 19.

Authors

Chris S Hodges¹, S Mick Tangparitkul^{1

2}

Affiliations

¹ School of Chemical and Process Engineering , University of Leeds , Leeds LS2 9JT , U.K.
² Department of Mining and Petroleum Engineering , Chiang Mai University , Chiang Mai 50200 , Thailand.

PMID: 31322888
DOI: 10.1021/acs.langmuir.9b01442

Abstract

In a recent article, Mondal et al. (Mondal, R.; Semwal, S.; Kumar, P. L.; Thampi, S. P.; Basavaraj, M. G. Langmuir 2018, 34, 11473-11483) demonstrated different patterns (coffee-rings and coffee-eyes) in dry deposits from solutions of concentrated well-stabilized nanofluids. Coffee rings created from dried sessile droplets result mainly from internal radial flow as proposed by Deegan et al. (Deegan, R. D.; Bakajin, O.; Dupont, T. F.; Huber, G.; Nagel, S. R.; Witten, T. A. Nature 1997, 389, 827-829). To generate coffee-eyes from pendent droplets, Mondal et al. have proposed a new particle transport route involving particle adsorption at the interface and its consequent curvature-driven settling along the interface due to gravity acting on the droplet. In this comment, we demonstrate that coffee-eyes can also be formed from pendent droplets by increasing the nanoparticle size to destabilize the colloidal liquid, causing nanoparticle accumulation at the water droplet apex without particle adsorption at the interface.