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Download or read book Nanoscale Structure and Dynamics of Entangled Polymer-grafted Nanoparticle Assemblies and Simple Linear Ethers Using Molecular Simulations written by Nicholas Thomas Liesen and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: In molecular dynamics (MD) simulations, coarse grained force fields significantly reduce the computational burden when predicting the structural properties of materials, but negatively impact the resulting transport property predictions, typically accelerating the dynamic evolution of the system. Using the methods of equilibrium and non-equilibrium MD simulations, the nanoscale structure of neat polymer grafted-nanoparticle (PGN) assemblies deposited on a smooth surface, and the transport properties of simple linear ethers are explored. Specifically, generic coarse grained bead-spring models are used to reach the time and length scales associated with entanglements, and to isolate the effect of architecture on the nanoscale structure and chain conformations of entangled and hexagonally packed PGN monolayers, which consist solely of nanoparticles (NPs) protected by grafted polymer chains. At increased graft densities brushes are dryer and more aligned, with decreased interpenetration between chains on neighboring canopies. This leads to fewer interparticle entanglements per chain, which are increasingly localized to interstitial regions. Chains also have increased alignment normal to the NP surface at high graft density, and increased intraparticle entanglement density near the surface. The inverse relationship between graft density and the degree of interparticle entanglement of the brush suggests that higher graft density monolayers will have reduced toughness and robustness under strain. Understanding these relationships, and generally connecting experimentally tunable parameters to molecular-scale structure and overall material properties, will provide insight into optimal design of future materials. In the second part of the thesis, finer transferable atomistic and united atom force fields are used to better capture trends in diffusivity and apparent viscosity across a range of temperatures and shear rates for a series of linear ethers. Specifically, trends in zero-shear viscosity with chain length, and force field performance relative to experiments are measured. Furthermore, there are consistent trends in activation energy barriers associated with diffusion and momentum transport across these models and experiments, as well as clear relationships between diffusive time scales, and rotational relaxation times, which are found to be inversely proportional to zero-shear viscosity. These time scales are explored as a means to gauge characteristic time scales of the system’s underlying dynamics, and are used to discuss whether the coarser united atom model can be treated as an accelerated version of its atomistic counterpart. Many transport properties, obtained by integrating equilibrium time correlation functions, are plagued by poor statistics. The relationships identified in this work may enable predictions of poorly behaved collective properties of the system, such as viscosity, from better behaved per-molecule properties, such as diffusion time and rotational relaxation time. Finally, by explicitly including the details of molecular conformations and intramolecular interactions, this work may help toward understanding the properties of fluids at a molecular level.