Spatio-temporal modulation of self-assembled central aggregates of buoyant colloids in sessile droplets using vapor mediated interactions

Hegde, O and Basu, S (2021) Spatio-temporal modulation of self-assembled central aggregates of buoyant colloids in sessile droplets using vapor mediated interactions. In: Journal of Colloid and Interface Science, 598 . pp. 136-146.

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Abstract

A functional sessile droplet containing buoyant colloids (ubiquitous in applications like chemical sensors, drug delivery systems, and nanoreactors) forms self-assembled aggregates. The particles initially dispersed over the entire drop-flocculates at the center. We attribute the formation of such aggregates to the finite radius of curvature of the drop and the buoyant nature of particles. Initially, larger particles rise to the top of the droplet (due to higher buoyancy force), and later the smaller particles join the league, leading to the graded size distribution of the central aggregate. This can be used to segregate polydisperse hollow spheres based on size. The proposed scaling analysis unveils insights into the distinctive particle transport during evaporation. However, the formation of prominent aggregates can be detrimental in applications like spray painting, sprinkling of pesticides, washing, coating, lubrication, etc. One way to avoid the central aggregate is to spread the droplets completely (contact angle ~ 00), thus theoretically creating an infinite radius of curvature leading to uniform deposition of buoyant particles. Practically, this requires a highly hydrophilic surface, and even a small inhomogeneity on the surface would pin the droplet giving it a finite radius of curvature. Here, we demonstrate using non-intrusive vapor mediated Marangoni convection (Velocity scale ~ O(1 0 3) higher than the evaporation-driven convection) can be vital to an efficient and on-demand manipulation of the suspended micro-objects. The interplay of surface tension and buoyancy force results in the transformation of flow inside the droplet leads to spatiotemporal disbanding of agglomeration at the center of the droplet. © 2021 Elsevier Inc.

Item Type:	Journal Article
Publication:	Journal of Colloid and Interface Science
Publisher:	Academic Press Inc.
Additional Information:	The copyright for this article belongs to Academic Press Inc.
Keywords:	Aggregates; Buoyancy; Contact angle; Drug delivery; Evaporation; Heat convection; Particle size analysis, Buoyant particles; Drug delivery system; Hydrophilic surfaces; Marangoni convection; Mediated interaction; Particle transport; Radius of curvature; Uniform deposition, Drops
Department/Centre:	Division of Mechanical Sciences > Mechanical Engineering
Date Deposited:	03 Aug 2021 09:44
Last Modified:	03 Aug 2021 09:44
URI:	http://eprints.iisc.ac.in/id/eprint/68902

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