Figure shows increasing aggregation of the Br-170 PNPls into stacks for more viscous solvents. Furthermore, these results corroborate the hypothesis that, for both I-110 and Br-170 samples, the undulations between 0.1 and 0.3 Å -1 are indeed the beginning of the stacking of the PNPls. Therefore, the concentration for this stacking in hexane is close to 80 mg/mL, which is a rather high concentration for nanocrystalline colloidal suspensions. We hypothesize that this stacking in liquids must occur in equilibrium: depending on the solvent, there is a mean size of the stacks, and the NPls from the extremes must go on and off the surface with a certain exchange rate. In addition, since the viscosity is inversely proportional to temperature, the solubility of the aggregates must increase at higher temperatures. Still, this temperature response must present some degree of hysteresis, as the data from Figure and Figure suggest.