Assembly Behavior of Hard and DNA-Programmable Colloidal Shapes into Complex Crystal Structures
Creators: name: Lee, Sangmin
Publisher: name: My University
Year: 2021
Subjects: subject: Self-assembly of colloids
subject: DNA nanotechnology
subject: Molecular dynamics simulation
subject: Monte Carlo simulation
subject: Thermodynamics
subject: Chemical Engineering
subject: FOS: Chemical engineering
subject: Engineering

description: Compared to atomistic assemblies with angstrom (Å) length scale, colloidal crystals at nanoscale often exhibit emergent and unique electronic, optical, mechanical and magnetic properties. Recent significant efforts in extending obtainable anisotropic shape and developing surface functionalization methods have enabled the design of a colloidal building block that assembles into a variety of structures and phases. However, the particle design space is highly multi-dimensional and is as yet mostly unexplored. Therefore, developing an easy and efficient model to study the assembly behavior of these particles is important. In this dissertation, using Monte Carlo and molecular dynamics simulations, we investigate the effect of particle shape and DNA functionalization of colloids on their assembly behavior. We first explore the assembly behavior of hard polyhedra, for which the entropy maximization is the sole driving force, with three projects. In the first project, we show two-step crystallization pathways via a metastable fluid-fluid phase transition in hard particle systems. We categorized our two-step crystallization pathways based on the dimension of the prenucleation motifs and discussed possible comparisons to other crystallization pathways. In the second project, we show entropy-driven self-assembly of five new open caged clathrate crystals stabilized by rotating guests. We demonstrate that crystallization of these crystals occurs via entropy compartmentalization, where the entropy of the system is decomposed into low entropy (host particles) and high entropy (guest particles) subsystems. In the third project, we show the formation and stabilization of fivefold and icosahedral twin clusters in a hard truncated tetrahedra system. We demonstrate that the icosahedral twin cluster can be entropically stabilized within a dense fluid due to a strong fluid-crystal interfacial tension. Next, we explore the assembly behavior of DNA-programmable colloids, in which the interaction between DNA ligands on the particle surface determines the assembly behavior. This part also covers three projects. In the first project, we show the formation of complex colloidal clathrate crystals using DNA-functionalized gold nano-bipyramids. The shape of bipyramid with 109.5o edge angle directs the particles to form a local tetrahedral network by maximizing DNA-hybridization, resulting in the formation of clathrate cages. In the second project, we introduce a symmetry breaking mechanism of DNA-programmable colloids, using mobile electron equivalents. We show that the spatial distribution of the electron equivalents in colloidal crystals varies depending on the DNA grafting density, resulting in the formation of nine different crystal structures. In the third project, we study the formation of diverse superstructures of Janus colloids functionalized by DNA. We show that colloidal chains of Janus particles form through cooperative assembly, and the formation of colloidal rings is catalyzed by introducing substrate binding through depletion. This dissertation shows that entropic bonds can be as effective as traditional chemical bonds in producing complex assembly behaviors and crystal structures, and the tunability of colloidal particles via DNA-functionalization allows us to find a rich set of new colloidal crystal applications.