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Identifier 000453918
Title Mathematical modeling and molecular dynamics simulations of polymeric nanocomposite materials
Alternative Title Μαθηματική μοντελοποίηση και προσομοιώσεις μοριακής δυναμικής νανοσύνθετων πολυμερικών υλικών
Author Παουέρ, Αλβέρτος Ιωάννης
Thesis advisor Χαρμανδάρης , Ευάγγελος
Reviewer Κατσαούνης, Θεόδωρος
Πλεξουσάκης Μιχαήλ
Αναστασιάδης Σπύρος
Μαυραντζάς, Βλάσης
Ρεμεδιάκης, Ιωάννης
Χρυσοπούλου, Κυριακή
Abstract The study of Polymeric Complex Materials is an intense research area due to the broad spectrum of systems, applications, length and time scales. For example, concerning hybrid Polymeric nanocomposite systems, nanoparticles are used to modify/enhance the thermodynamics, the mechanical properties and the dynamical/rheological behavior of the entire system. The aim of this work is to predict the heterogeneous behavior and properties of such complex systems. Detailed atomistic (united atoms) molecular dynamics simulations of several graphene based polymer (polyethylene, PE) nanocomposite systems have been performed. Systems with graphene sheets of different sizes have been simulated at the same graphene concentration (~3%). In addition, a periodic graphene layer (“infinite sheet”) has been studied. Results concerning structural and dynamical properties of PE chains are presented for the various systems and compared to data from a corresponding bulk system. The final properties of the material are the result of a complex effect of the graphene’s sheet size, mobility and fluctuations. A detailed investigation of density, structure and dynamics of the hybrid systems has been conducted. Particular emphasis has been given in spatial heterogeneities due to the PE/graphene interfaces, which were studied through a detailed analysis based on radial distances form the graphene’s center-of-mass. Chain segmental dynamics is found to be slower, compared to the bulk one, at the PE/graphene interface by a factor of 5 to 10. Furthermore, an analysis on the graphene sheets characteristics is presented in terms of conformational properties (i.e., wrinkling) and mobility. Moreover, we study the properties of polymer/gold nanoparticle (NP) nanocomposites through atomistic molecular dynamics, MD, simulations. We probe the structural, conformational and dynamical properties of polymer chains at the vicinity of a gold (Au) NP and a functionalized (core/shell) Au NP, and compare them against the behavior of bulk polyethylene (PE). The bare Au NPs were constructed via a systematic methodology starting from ab-initio calculations and an atomistic Wulff construction algorithm resulting in the crystal shape with the minimum surface energy. For the functionalized NPs the interactions between gold atoms and chemically adsorbed functional groups change their shape. As a model polymer matrix we consider polyethylene of different molecular lengths, from the oligomer to unentangled Rouse like systems. The PE/Au interaction is parametrized via DFT calculations. By computing the different properties the concept of the interface, and the interphase as well, in polymer nanocomposites with metal NPs are critically examined. Results concerning polymer density profiles, bond order parameter, segmental and terminal dynamics show clearly that the size of the interface/interphase, depends on the actual property under study. In addition, the anchored polymeric chains change the behavior/properties, and especially the chain density profile and the dynamics, of the polymer chain at the vicinity of the Au NP. In addition, the dynamics of polymer chains in poly(ethylene oxide) / silica nanoparticles, PEO/SiO2, nanohybrids has been investigated via atomistic molecular dynamics simulations. We study the effect of spatial confinement, induced by the nanoparticles, and of chain adsorption on the polymer structure and dynamics. Investigation of the static properties of the nanocomposites via detailed atomistic simulations reveals a heterogeneous polymer density layer at the vicinity of the PEO/SiO2 interface, which exhibits an intense maximum close to the inorganic surface with the bulk density reached for distances ~1-1.2nm away from the nanoparticle. For small volume fraction of nanoparticles, the polymer dynamics, probed by the atomistic simulations of low molecular weight chains at high temperatures, is consistent with the presence of a thin adsorbed layer that shows slow dynamics with the dynamics far away from the nanoparticle being similar to that in the bulk. However, for high volume fraction of nanoparticles (strong confinement) the dynamics of all polymer chains are predicted slower than that in the bulk.
Language English
Subject Polymers
Issue date 2023-03-17
Collection   School/Department--School of Sciences and Engineering--Department of Mathematics and Applied Mathematics--Doctoral theses
  Type of Work--Doctoral theses
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