The simulation results reveal that there are qualitative differences in the effect that cation size has on conductivity for different nanoparticle volume fractions (Figure ). For φ < 0.3, a nonmonotonic dependence on cation size is observed in which the conductivity first increases and then decreases with increasing cation size. In contrast, for φ > 0.3, the ionic conductivities are seen to monotonically decrease with increasing cation size. To rationalize these trends, we note that for all the cation sizes considered, the cation distribution on different site types in the multiparticle system (SI, Section S5.6) is similar to that noted for σ cat = 0.5 σ (Figure ). Accordingly, similar to the arguments presented to explain the results in Figure , the observed conductivity behavior with increasing cation size can be understood based on the corresponding trends for cation mobilities along the nonoverlapping and overlapping surface sites. Explicitly, for φ < 0.3, most cations are present on the non-overlapping surface sites (SI, Section S5.6) due to the negligible overlap between the surface sites of neighboring particles. From the results in Figure , the cation diffusivities in the non-overlapping surface region are seen to exhibit a nonmonotonic behavior with increasing cation size, which explains the corresponding conductivity trends. The behavior of cation mobilities in the non-overlapping surface region can in turn be attributed to the interplay between two competing factors: (a) faster cation transport for larger cations due to weakened ion-pair electrostatic interactions and (b) increased hindrance to the transport of larger cations due to their bulkiness. For φ > 0.3, with significant overlap between the surface sites of neighboring particles, the conductivity is primarily influenced by the cation diffusivities in the overlapping surface regions. The latter shows a monotonic decrease with cation size (Figure ) due to the greater impact of steric hindrance effects compared to ion-pair electrostatic interactions. Such characteristics serve to rationalize the monotonic conductivity behavior at higher nanoparticle loadings.