Solvent Effects in the Adsorption of Alkyl Thiols on Gold Structures:  A Molecular Simulation Study

Abstract

We carried out Monte Carlo simulations of gold nanocrystals (NCs) and (111) slabs covered with alkyl thiols, with and without explicit solvent (n-hexane), at T ) 300 K. Adsorption isotherms for propane-and octanethiol showed a phase behavior measured previously in experiments. Comparison of the adsorption isotherm of octanethiol in hexane on a (111) slab with experimental data suggests that, in this system, no thiolate bond was formed. The geometry of a gold surface strongly influences the formation and structure of the capping monolayer. On a (111) surface, attractive interactions between carbon chains are more pronounced than on a NC. This leads to a stronger penetration of the capping layer by the solvent. Adsorption selectivity for binary alkyl thiol mixtures is stronger in vacuum than in solution. The convex shape of the NCs also reduces the adsorption selectivity of binary thiol mixtures. This result shows that the solvent cannot be ignored in simulations.

Understanding interactions between capped nanocrystals: Three-body and chain packing effects

“…The binding of thiol headgroups to Au surfaces is better understood than for other NC-surfactant systems. 16 Several models have been successfully applied to describe the structure and thermodynamics of alkyl thiol monolayers on flat Au͑111͒-surfaces [17][18][19] and Au-NCs. [18][19][20][21] It is important to note that the effective NC-NC interactions in a solvent are very different from the ones in vacuum due to solvent-capping layer interactions.…”

“…16 Several models have been successfully applied to describe the structure and thermodynamics of alkyl thiol monolayers on flat Au͑111͒-surfaces [17][18][19] and Au-NCs. [18][19][20][21] It is important to note that the effective NC-NC interactions in a solvent are very different from the ones in vacuum due to solvent-capping layer interactions. The work of Patel and Egorov 22 focused on the PMF for very small capped NC cores ͑Au 38 ͒ for varying solvent quality, and it was found that the PMF can be tuned from strongly attractive to fully repulsive.…”

A computer simulation study of the interaction between passivated and bare gold nanoclusters

“…We have noted the effect of the chain attachment on the nanocore structure before (Lal et al 2004(Lal et al , 2006. The behaviour of the chains on the metal surface has been shown by Pool et al (2007) to be dependent on the curvature of the surface. On flat surfaces, when the chain attachment density is suitable, the chains form a layer with a common angle of alignment, but such an alignment is normally frustrated by surface curvature.…”

“…Egorov (2005) devised a model for the nanoparticle interaction based on the classical density functional theory and Patel & Egorov (2007) performed molecular dynamics simulations similar in character to those presented there. Schapotschnikow et al (2007aSchapotschnikow et al ( ,b, 2008, Schapotschnikow & Vlugt (2009) and Pool et al (2007) have completed a comprehensive series of simulation studies, including a study of nanoparticle interactions (Schapotschnikow & Vlugt 2009), that is also highly relevant. Much of what we report here for passivated nanoparticles partly confirms what these authors have found; however, our model is sufficiently different in detail to show effects not previously reported and shed additional light on the subject.…”

Coarse-grained model for gold nanocrystals with an organic capping layer

“…[15][16][17][18][19] Due to high computational cost, only few studies investigated properties of systems with several NCs. 16,20,21 The NCs in those studies were relatively small (up to 140 atoms) compared to the ones typically used in assembly experiments.…”