Doctor of Philosophy (PhD)
A multiscale framework for simulation of fluid flow is developed by using a hybrid atomistic-continuum approach to couple molecular dynamics (MD) to the incompressible Navier-Stokes equations. The framework incorporates the accuracy of atomistic methods to resolve the detailed physics at the nano- to micro-scale in regions with large gradients, and the efficiency of the continuum models to describe the rest of the fluid. A state exchange scheme is employed where the value of conserved variables are reciprocated between the atomistic and continuum descriptions. A polyatomic constrained dynamics is introduced to facilitate construction of the required atomistic information from the corresponding continuum domain. The developed framework is demonstrated by studying flow field evolution in shear driven Couette flows, ranging from simple Lennard–Jones liquids to complex ones such as water and alkanes. The molecular details of interfaces at solid–fluid and fluid–fluid under shear are investigated and compare them with results from analytical predictions. As a prelude to developing the ability to handle large nanoparticles within the multiscale framework, the interaction of nanoparticles in water with planar polymeric walls is investigated by means of molecular dynamics and free energy calculations. A mean-field approximation is employed to represent an apolar fullerene-based nanoparticle as a spherical colloid which enables continuous variation of the solute size. This allows for a systematic size-dependent study of the solute potentials of mean force (PMFs) and solvation forces as a function of solute–wall distance. It is shown that the solute has a strong tendency for deposition onto the PMMA surface. However, for solutes with diameters greater than 3 nm a free energy barrier starts to hinder the solute–surface deposition. The transition from barrierless PMFs at small solute sizes to PMFs with barriers at larger solute sizes is attributed to the loss of hydrogen bonding between water molecules in proximity to the solute which intensifies the role of the comparatively weak, attractive van der Waals interactions between the water molecules and the solute, and the enlarged solute surface which makes depletion of the last layers of water trapped between the solute and the wall extremely expensive.
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Fattah Hesary, Kasra, "Hybrid Atomistic–Continuum Simulation Methodology for Handling Nanoparticle- Wall Interaction" (2017). LSU Doctoral Dissertations. 4219.
Nikitopoulos, Dimitris E.