The effect of AuNP in solvent diffusion extends at least to 5
nm from the AuNP center (3 nm from the surface, Figure 9),
which indicates that the solvent transmits the interaction shellby-
shell by intermediating the orientation of water molecules.
This phenomenon is evident in the solvent orientation data
shown for the AuNP solutions in Figure 10. As for the shorttime
diffusion analysis, the water orientations also depend
strongly on distance: The first shell surrounding the NH3
+
terminal groups aligns water molecules in such a manner that
oxygen is closer to AuNP+ than the H atoms, and vice versa for
AuNP−. This effect arises from the electrostatic forces (of Hbonding)
between the oppositely charged terminal groups of
AuNPs and polarized water molecules, and it results in opposite
trends for the two AuNPs.