Engineering Assembly of Polyhedral Particles Toward Complex Structures and Pathways

Nanoparticle (NP) self-assembly is a versatile bottom-up approach to design and synthesize novel functional materials. Thermodynamics and kinetics of the self-assembly are governed by many factors, such as the shape of the nanoparticles, surface ligand, pH, salt concentration of the solution, temperature, and so on. It is not trivial to understand multiplicity of variables in the assembly behavior but is crucial for developing design principles to obtain target assemblies with desired properties. In this dissertation, I investigated the self-assembly of polyhedral NPs using Monte Carlo and molecular dynamics simulations. I focused on understanding how the shape of particles and the energetic interactions between particles affect their self-assembly behavior. In the first project, I investigated entropy-driven self-assembly of hard bipyramid systems with varying aspect ratios and symmetries. I showed that diverse colloidal superstructures with various symmetries and complexities can be obtained by tuning the shape of bipyramid particles. I found some bipyramids are mesogenic and they show different mesophase transition behavior. I demonstrated that the crystallization pathways as well as the transition behavior involving mesophases can be modulated by tuning the bipyramidal shape. In the second project, I studied DNA-mediated assembly of decahedral NPs into a dodecagonal quasicrystal in collaboration with Mirkin group at Northwestern University. I showed that the quasicrystal phase which is metastable in a hard particle system with the same particle shape can be stabilized by the enthalpic interaction between particles driven by DNA ligands. Moreover, I showed that the quasicrystal has an intrinsic stacking disorder along the 12-fold symmetry axis due to frequent phason flips, which entropically contributes to the stability of the quasicrystal. In the third project, I investigated the assembly of chiral tetrahedra into helical superstructures. Using a pair potential model representing the shape, chiral ligand, and charge interactions, I showed that the modeled tetrahedra self-assemble into 1D tetrahelices by precisely tuning the short-range attraction and long-range repulsion. I showed that the chiral bias induced by the ligand propagates to the superstructures leading to the highly enantioselective assembly of tetrahelices. Nextly, I suggested a hierarchical assembly route from tetrahedra into helical bundles via tetrahelices, which can be rationalized by the fusion of tetrahedra and subsequent charge renormalization. I expect these works provide guidance for proper selection of the building block and the assembly conditions to assemble desired nanoparticle superstructures.PhDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/174656/1/yeinlim_1.pd