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

Abstract

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. Accordingly, the dried pattern is composed of distinct regions of closely bound ordered Au-NP assemblies coexisting with loosely bound disordered packings of Au-NPs that form inside and outside the coffee stain pattern. The multilayers of densely packed and hexagonally arranged Au-NPs at the outer coffee stain edge are tested for surface-enhanced Raman scattering activity against a standard probe molecule (Rhodamine B—RhB). The least detection limit of RhB at the outer coffee stain edge improves by three orders of magnitude with increasing nanoparticle concentrations and nanoparticle sizes. The present study demonstrates that the drying kinetics, distinct dried deposit morphologies, and the limit of plasmonic activity of the deposited Au-NPs can be fine-tuned via a combined variation of CTAB concentration, nanoparticle size, and nanoparticle concentration in the Au-NP dispersion droplet.