(4nw) Reconfigurable Nano Cube Superlattice Assemblies Elucidated with Dimensional Analysis

Research Interests: I am broadly interested in simulations of collective phenomena and self-assembly. I am particularly interested in soft matter biophysics. Since my PhD primarily focused on self-assembly of nanoparticles, I am well primed to pivot into this blossoming field. I plan on bringing some classic tools of chemical engineering, including scaling theory and dimensional analysis to new problems in biological soft matter. My abstract below shows off a particular case where the dimensional analysis and theory I developed tied the simulation and experiments of this project together.

Reconfigurable Nanoparticle superlattices where assembly is observable in-situ, are incredibly rare due to the challenges of imaging and analyzing such systems on a per particle level. Furthermore, a grand challenge of nanoparticle self-assembly is reconfiguring between two distinct lattices, while measuring and predicting the process of self-assembly. In this work, we take the first major step in this challenge by tuning the self-assembly of gold nanocubes under TEM illumination by changing the solvent in which the nanoparticles self-assemble. Under the TEM beam, we hypothesize that the nanoparticles become charged, and that the solvent undergoes radiolysis which screens the electrostatic repulsion between nanoparticles. Attraction between nanoparticles is induced via Van der Waals (VdW) forces. By building a simulation model that captures VdW attraction and electrostatic repulsion, we accurately predict the phases that assemble in experiment and their pathway. Furthermore, through dimensional analysis, we show that the self-assembly process can most likely be explained via a change in the screening length of the solvent not via a change in the magnitude of repulsion between the nanoparticles. Additionally, we use our model of electrostatic repulsion and VdW attraction to predict the boundary between orientationally ordered and disordered superlattices, allowing us to tune the assembly of rotator crystals. Finally, we leverage our understanding of different solvents to in-situ reconfigure our lattices and compare the mechanism of reconfiguration to simulations. Our combined simulations, dimensional analysis, and experiments thereby elucidate the mechanism of self-assembly for these reconfigurable nanoparticle superlattices whose pathway of assembly can be observed in-situ for the first time.