Wetting Properties of Passivated Metal Nanocrystals at Liquid−Vapor Interfaces: A Computer Simulation Study

Abstract

Molecular dynamics simulations have been employed to determine the contact angles of alkylthiol passivated gold nanocrystals adsorbed at the air-water interface. Simulations were performed using butane-, dodecane-, and octadecanethiol passivated nanoparticles. We demonstrate how the length of the surfactant chain can profoundly influence the wetting behavior of these nanoparticles. All particles were found to be stable at the air-water interface, possessing large, well-defined contact angles. We find that the shape of the dodecane- and octadecanethiol particles is strongly perturbed by the interface. We also present an analysis of the orientational ordering of water molecules at the dodecane-water interface and around butane- and dodecanethiol passivated nanoparticles. The orientational ordering translates into an electrostatic field around the nanoparticles, the magnitude of which corresponds with that of the water liquid-vapor interface.

Contact angle and adsorption energies of nanoparticles at the air–liquid interface determined by neutron reflectivity and molecular dynamics

“…The contact angle for d-OT-coated NPs is in line with the values obtained in previous theoretical reports of alkanethiol NPs. Tay and Bresme 30 reported using molecular dynamics simulations a contact angle of 115°for butanethiol and 140°for dodecanethiol coated gold clusters Au 140 . Our result for NPs covered by an alkanethiol with an intermediate length between those two ligands shows a contact angle value (∼120°) that lies in that range despite the difference in the NP core size.…”

“…One important consideration of Tay and Bresme's work is that they observed a deformation of the shell, that changed from a purely spherical into a lens-like shape for long ligands, giving rise to two contact angles. 30 This effect arises probably from the large thiol length/core radius ratio that increases the space between ligands on the parts separated from the core allowing a bigger deformation. In the NPs investigated in this work (Au 3832 -d-OT 476 ), that involves a smaller length/core radius ratio, we do not observe significant deformations.…”

How stable are amphiphilic dendrimers at the liquid–liquid interface?

“…For example using atomistic molecular dynamics simulations Tay and Bresme predicted the contact angle, particle shape and orientational order of the water molecules for one alkylthiolpassivated gold nanoparticle adsorbed on the air--water interface. 22 More recently an atomistic model has also been used to simulate amphiphilic dendrimer at the air/water interface. 23 The simulations have showed that the flexible polyaminoamide (PAMAM) dendrimers functionalized with long aliphatic chains adhere to the air/water interface adapting their molecular conformation to the polar/apolar environment.…”

Adsorption of core-shell nanoparticles at liquid–liquid interfaces

“…Numerical simulations have started to address the shell conformation for individual particles at liquidliquid interfaces, but the studies are still limited to relatively short dispersants. 38,39 Preliminary experimental studies have highlighted a link between polymer molecular weight and colloidal stability at the interface. 40 We focus here on SALI of iron oxide NPs, which find numerous applications due to their magnetic properties and good biocompatibility, 41 including diagnostics 42 and therapeutics, e.g.…”