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CBE Doctoral Dissertation Defense: “Computational Analysis of Colloidal Self-Assembly with Interaction Heterogeneity” (Po-Ting Wu)
July 3 at 2:00 PM - 4:00 PM
Abstract:
Micron-scale colloidal particles with short-ranged attractions, e.g., colloids functionalized with single-stranded DNA oligomers, have emerged as a powerful platform for studying colloidal self-assembly phenomena with the long-term goal of identifying routes for metamaterial fabrication. Although these systems have been investigated extensively both experimentally and computationally, the role of ‘real world’ features that may impact self-assembly in unexpected ways have been largely ignored. One such example of an important, yet underappreciated, feature is interaction heterogeneity (IH), i.e., variations in interparticle interaction strengths across a population of particles, which can arise from variability in the DNA strand areal density on particle surfaces during fabrication. In this thesis, we systematically investigate the impact of IH on equilibrium and non-equilibrium self-assembly processes in colloidal systems.
First, we refine a physics-based interparticle interaction model for DNA-functionalized colloids. Rather than recalculating interactions for varying DNA strand areal densities while implementing IH, we propose a simplified approach by assigning a scalar binding modulator to each particle to scale interactions. This approach is shown to accurately and efficiently represent variations in DNA strand areal density. In the remainder of this thesis, we use this interaction model to investigate the effects of IH on equilibrium and non-equilibrium self-assembly behaviors. Using a multicomponent coexistence tracing approach originally developed for size polydispersity, we compute phase diagrams for both Gaussian and bidisperse IH distributions. Our results reveal that IH shifts the fluid-side coexistence boundaries outward, promoting crystallization at lower particle volume fractions while also resulting in crystals that are enhanced in the stronger binding species. Both Gaussian and bidisperse IH show qualitatively similar effects, suggesting that even relatively simple IH distributions produce the observed effects.
Under non-equilibrium conditions, we study colloidal gelation induced by thermal quenching. In these non-equilibrium simulations, crystallization is inhibited with size polydispersity so that gelation can be studied under a wide range of IH and quenching conditions. We find that IH spreads out the gelation processes in time whereby particles with higher binding modulators initiate gelation and weaker particles subsequently decorate the gel backbone. Although the influence of IH on macroscopic gel structures, e.g., structure factor, appears to be subtle, significant differences are observed at the local structural level, notably captured by the coordination number distribution. Overall, our results emphasize that IH profoundly impacts both equilibrium and non-equilibrium colloidal self-assembly behaviors, providing a new perspective on IH as a new control parameter for colloidal self-assembly.
Zoom Meeting ID: 94650952409

Po-Ting Wu
CBE PhD Candidate
Advisor: Talid Sinno (CBE)
Committee Members: John C. Crocker (CBE), Robert A. Riggleman (CBE), Arjun G. Yodh (Physics and Astronomy)