Unraveling the Role of Excess Ligand in Nanoparticle Pattern Formation from an Evaporatively Dewetting Nanofluid Droplet

Abstract

Nanoparticle (NP) patterning on a solid surface via nanofluid droplet evaporation is one of the most fascinating topics of research. Quite intriguingly, though a dose of excess ligand has been invariably included in all of the experimental studies that resulted in large-area NP patterns, the role of this excess ligand has been addressed inadequately in the modeling studies carried out so far. Addressing this, we have conducted systematic studies by including excess ligand both in our experiments and modeling, and correlated the results with each other. For this, we prepared nearly monodispersed thiol-protected gold nanoparticle dispersion in toluene and added calculated amounts of excess thiol before drop-casting it onto a transmission electron microscopy (TEM) grid. Subsequently, upon solvent evaporation, the patterns formed were imaged using conventional electron microscopy and analyzed with customized image processing tools, to perform statistically significant measurements. Our study demonstrates the ability of soluble excess ligand to induce NP aggregation under nonequilibrium condition, leading to large-area monolayer formation. These experimental results were then rationalized by Monte Carlo simulations, based on a modified coarse-grained two-dimensional (2D) lattice-gas model. We found that excess ligand facilitates NP spinodal phase separation under nonequilibrium conditions, largely governed by the interplay between ligand–solvent and nanoparticle–ligand interactions. Using power spectrum density analysis, we clearly demonstrate that these spatial patterns have fractal surface characteristics due to persistent fractional Brownian motion within subdiffusion limit.

Topological phases in nanoparticle monolayers: can crystalline, hexatic, and isotropic-fluid phases coexist in the same monolayer?

“…Large area NPMLs are reported to form at this particle and excess ligand concentration. 44 During this time particles are completely immersed within the solvent and interacting mainly through Brownian motions. At the later stage, the thin solvent film (a pseudo 2D environment for the NPs) gets formed with the NPs (being sub 10 nm in size) still being immersed.…”

Influence of van der Waals Interactions between the Alkyl Chains of Surface Ligands on the Size and Size Distribution of Nanocrystals Prepared by the Digestive Ripening Process

“…The recipe was prepared to calculate the size and size distribution from the TEM images from each sample. The details about the recipe can be found in ref .…”

Conducting Gold Nanoparticle Films via Sessile Drop Evaporation

“…Evaporation of gold nanoparticle dispersion is a common method for the fabrication of particulate films with high operational stability. 21 However, the electrical conductivity of the particulate films produced via droplet evaporation is low due to the presence of voids and the lack of particle−particle contacts. 22 In this context, several strategies have been reported by the researchers to design a conducting film.…”