Janus Gold Nanoparticles from Nanodroplets of Alkyl Thiols: A Molecular Dynamics Study

Abstract

Janus particles provide an asymmetry in structure, which can impart diverse functionalities leading to immense importance in various applications, ranging from targeted delivery to interfacial phenomena, including catalysis, electronics, and optics. In this work, we present results of a molecular dynamics study of the growth mechanism of coating on gold nanoparticles (AuNPs) from droplets of n-alkyl thiols with different chain lengths (C5 and C11) and terminal groups (CH and COOH). The effect of chain lengths and functional groups on the formation of a monolayer of alkyl thiols on AuNPs is investigated. A two-step mechanism, initiated by the binding of the droplet to the nanoparticle surface with a time constant on the order of ∼1 ns, followed by the diffusion-driven growth with a larger time constant (on the order of 100 ns), is shown to capture the growth dynamics of the monolayer. It is observed that the time required for complete wetting increases with an increase in the chain length. Moreover, the monolayer formation is slowed down in the presence of carboxyl groups because of strong hydrogen bonding. The kinetics of the n-alkyl thiols coating on the nanoparticles is found to be independent of the droplet size but carboxyl-terminated thiols spread more with increasing droplet size. Furthermore, different time constants for different chains and functional groups yield Janus coating when two droplets of alkyl thiols with different terminal groups are allowed to form monolayers on the nanoparticle. The Janus balance (β) for different combinations of alkyl thiols and nanoparticle sizes varies in the range of 0.42-0.71.

Computational and Experimental Investigation of Janus-like Monolayers on Ultrasmall Noble Metal Nanoparticles

“…Large, patchy, Janus-like domains can clearly be seen. This type of phase separation is consistent with previous simulation work that suggests that chemical mismatch induces patchy monolayer phase separation. ,− …”

“…Work by Glotzer et al and Stellacci et al used dissipative particle dynamics with a soft repulsive potential to model ligand monolayers. While these studies provide insight on the effects of physical and chemical mismatch on phase separation in the ligand monolayers, the simulations do not explicitly include attractive interactions between ligands or nanoparticle faceting, both of which have been shown to be important in subsequent work on NP , and flat monolayer phase separations. Other groups have modeled NP monolayers using molecular dynamics. , However, the equilibration of thiol monolayers in the laboratory can take up to 4 days, making it impossible for traditional molecular dynamics simulations to reach equilibrium.…”

“…While these studies provide insight on the effects of physical and chemical mismatch on phase separation in the ligand monolayers, the simulations do not explicitly include attractive interactions between ligands or nanoparticle faceting, both of which have been shown to be important in subsequent work on NP , and flat monolayer phase separations. Other groups have modeled NP monolayers using molecular dynamics. , However, the equilibration of thiol monolayers in the laboratory can take up to 4 days, making it impossible for traditional molecular dynamics simulations to reach equilibrium. Our own previous work used self-consistent field theory (SCFT) to model the nanoparticle monolayer. , SCFT determines the equilibrium monolayer configuration by solving a set of self-consistent equations.…”

Pt–Co nanocluster in hollow carbon nanospheres

“…The temperature of the systems was controlled using Nosé–Hoover thermostat with a relaxation time of 0.1 ps. Previous works have also used successfully the same relaxation time for this thermostat . To investigate whether our systems have been achieved the equilibrium and stability, we have drawn the graphs of configurational energy, total energy, and temperature versus the simulation time for the different systems considered in this work and presented in Supporting Information Figures S5–S7.…”

Influence of Temperature-Guided SAM Growth on Wetting and Its Mass Transfer Models

“…34,35 The chain length of the molecules is also a crucial factor in governing the structural behaviors of the adsorbed monolayers. 30,48 Longer chains promote enhanced molecular packing and ordering within the monolayers, leading to more well-defined and organized structures. 49 Previous studies demonstrated that alkanol molecules form a strongly adsorbed monolayer on a hydrophilic surface, such as mica.…”