When 10:00 AM - 12:00 PM Apr 29, 2015
Where NCRC Bldg. 10, Level 1, Research Auditorium
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Tuning Mesoscopic Assembly Behavior via Nano Building-Block Interactions and Architecture

Ryan Marson
Thesis Defense

Sharon Glotzer, advisor


Using molecular dynamics (MD) computer simulations we show that a variety of complex, technologically relevant phases emerge from tuning aspects of nanoparticle architecture and interactions. In doing so, we demonstrate that nanoparticles can be thought of as building-blocks in larger scale assemblies over which we can tune nearly every aspect of the structure for specific applications such as photonics, photovoltaics, or catalysis. We highlight three specific case studies - polymer/nanoparticle composite building-block assemblies, star polymer microdroplets, and amino-acid coated nanoparticles with embedded dipoles that form rods of preferred chirality. In all cases predictions from simulations are used to either guide building-block assembly or to offer detailed insight into structures that were not previously understood. Additionally, we establish general, domain-agnostic mesophase behavior, as well as hypothesize synthesis and assembly strategies to target highly specific structures for any given application.


In the first study, we show that tethered nanoparticle building blocks can assemble phases such as lamellae, micelles, and network phases such as the double gyroid. These results are corroborated by experimental findings in systems of polyhedral oligomeric silsesquioxane (POSS) with attached polystyrene (PS) tethers; in both the computational and experimental systems identical mesophases emerge as the length of the polymer tether increases. We demonstrate specific transitions between hexagonal tubes, Frank-Kasper phases, and the Sigma-phase quasicrystal approximate for this building-block.


Our second study uses a modification of MD, dissipative particle dynamics (DPD), to establish the role of unreacted hydroxyl star polymer end-groups in stabilizing microdroplet assemblies. We show that by changing both the length and number of the polymer arms we can tune between 3 types of mesoscopic assemblies - porous, non-hollow, and hollow droplets. We confirm that a critical hydroxyl density is necessary to trigger the hollow to non-hollow droplet transition. Additionally we show that porous structures emerge for short polymer arm lengths.


Finally, our third study demonstrates that local nanoparticle interactions can bias the bulk chirality in a pseudo-1D assembly. By coating CdTe nanoparticles with a chiral amino-acid stabilizer, Cysteine, it is possible to predictably bias the handedness of rods and wires created from the nanoparticles. Via simulation, we establish that local twist originating from the Cysteine coating on the nanoparticle surface can locally bias assemblies. Additionally, we demonstrate that the pitch and structure of the rod can depend critically on the nanoparticle shape.