The influences of surface polar unit density on the water dispersity of nanoparticles

Abstract The impacts of surface polar unit density on the water dispersity of nanoparticles have been investigated using molecular dynamics simulations. The nanoparticles with various polar unit densities were designed by assigning partial charges on different numbers of surface atoms of C60s. The water dispersity of the nanoparticle is enhanced rapidly as the introduction of surface polar atoms. Nevertheless, when the number of polar atoms (N) grows beyond a certain value, the change in the nanoparticle's water dispersity is relatively small. The hydration behaviors of nanoparticles were then studied to investigate the dependence of water dispersity on the surface polar unit density. The introduction of surface polarity enhances the interaction potential between the hydration water and the nanoparticle (Uwater−NP) which should facilitate the dissolution of nanoparticles. On the other hand, the surface polarity also reduces the number of hydrogen bonds formed by a water molecule in the hydration layer with other water molecules (NHB) and enhances the interaction potential between the contacted nanoparticles (UNP−NP) which may hinder their dispersion. However, Uwater−NP, NHB, and UNP−NP all change non-monotonically with N. Moreover, the surface polarity also rearranges the hydration structure of the nanoparticle, which also changes non-monotonically with N. The dependence of the nanoparticle's water dispersity on the surface polar unit density should be attributed to the interplay of different aspects of nanoparticle's hydration behavior, especially the interplay of Uwater−NP, UNP−NP, and NHB.