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arXiv · 2002.01362

Gold Nanoparticles Passivated with Functionalized Alkylthiols: Simulations of Solvation in the Infinite Dilution Limit

Saurav Prasad·Madhulika Gupta
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Abstract

Solvation of gold nanoparticles passivated with end group functionalized alkylthiols, namely CH$_3$, NH$_2$ or COOH is studied in solvents of varying degrees of repulsion-dispersion and electrostatic interactions ranging from strongly polar SPC/E water to modified hybrid water models, where the Lennard-Jones contribution to the potential energy is enhanced relative to SPC/E to completely non-polar, decane. The effects due to solvent reorganization around the nanoparticle as a function of the ligand and solvent chemistry are monitored using the nanoparticle-solvent pair correlation functions and tetrahedral order parameter. The solvent penetration inside the ligand shell is maximum for decane, indicating better solute-solvent interaction in decane compared to other solvents. The COOH end group functionalized nanoparticle breaks the tetrahedral structure of water molecules more as compared to other nanoparticles used in this study. The ligand reorganization and its effect on solvation are monitored using radial density profiles (RDPs), radius of gyration ($R_g$) and ligand asymmetry parameter ($\langle \Delta \rangle$). RDP and $R_g$ values show significant stretching of ligands in decane than in model waters, which is also consistent with $\langle \Delta \rangle$. The ligand shell anisotropy for all nanoparticles is maximum in SPC/E water and minimum in decane. The isotropic potential of mean force ($V_{PMF}(r)$) between two identical end group functionalized nanoparticles have been calculated in vacuum, SPC/E water and H3.00 modified hybrid water, which consistently shows attractive well depth. Distance-dependent fluctuation driven anisotropy has also been examined. The implications for self-assembly of passivated gold nanoparticles from aqueous dispersions as well as the dependence of calculated quantities on ligand and solvent chemistry are highlighted.

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Saurav Prasad, Madhulika Gupta. 2020-02-04. Gold Nanoparticles Passivated with Functionalized Alkylthiols: Simulations of Solvation in the Infinite Dilution Limit. https://arxiv.org/abs/2002.01362

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