Effect of Water Vapor on the Pair Potential Between Ligated Nanoparticles

We have carried out all-atom molecular dynamics simulations to illuminate the physical basis for the change in Young’s modulus of a monolayer of dodecane thiol ligated Au nanoparticles discovered by Wang et al.[1] For a water vapor concentration that would generate 80% monolayer coverage of the nanoparticle surface we find that water molecules form large fluctuating “hemispherical” clusters on the nanoparticle surface with the correct macroscopic contact angle. We have constructed AuNP-AuNP potential curves for both wet and dry systems; the difference in the shapes of these curves near their minima is consistent with the change in Young’s Modulus found by Wang et al.[1] The in vacuum all-atom NP ligand conformations and NP-NP potential agrees well with those previously obtained from united-atom simulations.[2] Additionally, both the wet and dry potential energy curves differ significantly between sampled frozen orientations, implying the possibility of variation in the local NP energy in a self-assembled ordered AuNP array.

[1] Wang, Y. et al. ACS Nano 11, 8 (2017)
[2] Liepold, C. et al. J. Chem. Phys. 150, 044904 (2019)