The deviations between the ion distribution data and the DH
descriptions emerge around 2.4 nm from the AuNP center of
mass, which can be considered as an approximate location for
the interface (often called a double layer) between NP-bound
and loosely associated counterions, the latter being able to
move rather freely in the system despite the presence of the
NP. The fits shown in Figure 6 yield values of 0.27 and 0.20 nm