Mesocrystal to single crystal transformation of D,L-alanine evidenced by small angle neutron scattering

The formation of D,L-alanine mesocrystals and their transformation into a single crystal was investigated by time-resolved small angle neutron scattering (SANS) and dynamic light scattering (DLS). Whereas DLS was able to monitor the early nanoparticle growth stages and the initial aggregation process to a mesocrystal, which was shown to scatter like a single crystal in a previous study, SANS was able to characterize the micron sized nanoparticle superstructure: the mesocrystal. With time, the mesocrystal structure became compact as evidenced by a transition from the Q^-3 power law behavior characteristic for aggregates with inner surface in the beginning and later a transition to Q^-4 behavior characteristic for compact particles: the single crystal. This is the first time-resolved experimental evidence that a compact single crystal can be formed by transformation of a mesocrystal nanoparticle aggregate by crystallographic fusion of the building units.