Title:	Correlating the drying kinetics and dried morphologies of aqueous colloidal gold droplets of different particle concentrations
Authors:	Zaibudeen, A.W. Bandyopadhyay, Ranjini
Issue Date:	Aug-2022
Publisher:	Scinece Direct
Citation:	Colloids and Surfaces A, 2022, Vol. 646, Article No. 128982
Abstract:	The evaporation of a gold nanorod (Au-NR) dispersion droplet, containing residual surfactant, on a hydrophilic silicon substrate results in a coffee stain with different microstructures. The distinct regions in the coffee stain, formed during different stages of droplet drying, are presumably correlated with the dynamics of the evaporating droplet. We drop-cast 2 μL CTAB capped Au-NR dispersion droplets on a hydrophilic substrate, and study their evaporation kinetics, and dried patterns using optical, electron, and atomic force microscopy. We report that droplet retraction, pinning, and quick evaporation during the initial, intermediate, and final phases of droplet drying are clearly correlated with the different coffee stain aggregation regions for a range of Au-NR concentrations. The receding velocity of the evaporating gold colloidal droplet decreases with increasing Au-NR concentration, resulting in random to cluster-like aggregations of Au-NRs outside the coffee stain. Droplet depinning is followed by a concentration-dependent droplet pinning process which results in the formation of a coffee stain edge comprising distinct domains that consist of smectic phase-like structures of Au-NRs. The duration of droplet pinning, the widths and heights of the outer coffee stain edge increase with increasing gold nanorod concentration and are consistent with theoretical predictions. Finally, the rapid evaporation of the droplet leads to the formation of non-uniform depletion region and inner coffee stain regions. Our study demonstrates that the solute deposition pattern can be tailored by controlling the evaporating droplet kinetics. The unique assemblies of Au-NRs in the coffee stain edge are potentially excellent candidates for the development of plasmonic sensors for the selective detection of trace amounts of molecules, while the large clusters of end-to-end aligned Au-NRs outside the stain could be used for the fluorescence enhancement of low quantum yield molecules.
Description:	Restricted Access.
URI:	http://hdl.handle.net/2289/7924
ISSN:	0166-6622
Alternative Location:	https://doi.org/10.1016/j.colsurfa.2022.128982
Copyright:	2022 The Author(s)
Appears in Collections:	Research Papers (SCM)

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