Combined effects of nanoparticle size, and nanoparticle and surfactant concentrations on the evaporative kinetics, dried morphologies, and plasmonic property of gold colloidal dispersion droplets.

Understanding the combined influence of various parameters on the formation and morphologies of distinct solute deposit patterns obtained after droplet drying is essential for developing numerous real-time applications. In this work, gold nanoparticle (Au-NP) dispersion droplets are dried on a hydrophilic substrate and the coupled effects of nanoparticle size, and nanoparticle and surfactant (CTAB) concentrations on the evaporative kinetics and evaporation-induced nanoparticle assemblies in dried deposit patterns are studied using optical and scanning electron microscopy. The distinct stages of drying of a cetyltrimethylammonium bromide (CTAB) stabilized Au-NP dispersion droplet, such as the evolutions of pinning, depinning, and a depletion region, change drastically for a combined increase of CTAB concentration and nanoparticle size for different nanoparticle concentrations.

DC field coupled evaporation of a sessile gold nanofluid droplet.

The coffee stain formed when a sessile nanofluid colloidal droplet dries on a substrate displays distinct nanoparticle aggregation regimes. We employ scanning electron microscopy to study the coffee stain morphologies when DC electric fields are applied to drying aqueous suspension droplets of CTAB capped gold nanorods (Au-NRs) on a hydrophilic substrate. We observe a typical coffee ring edge with several Au-NR domains due to outward capillary flow both in the absence and presence of the electric field.