Date of Award

August 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Nidal Abu-Zahra

Second Advisor

Deyang Qu

Committee Members

Junjie Niu, Benjamin Church, Jorg Woehl

Keywords

battery, binder, drug carrier, finite element analysis, molecular dynamics, polymer

Abstract

This study presents three tailored models for popular problems in energy storage and biological materials which demonstrate the application of computational materials science in material system development in these fields. The modeling methods can be extended for solving similar practical problems and applications.

In the first application, the thermo-mechanical stress concentrated region in planar sodium sulfur (NaS) cells with large diameter and different container materials has been estimated as well as the shear and normal stresses in these regions have been quantified using finite-element analysis (FEA) computation technique. It is demonstrated that the primary failure mechanism in the planar NaS system design considered in the current work would be the interfacial fracture between the insulating header (IH) and the upper insert metal (IM1) due to the normal stress in cell height direction, and the necessary treatments, including better material selection or improved bonding technology between IH and IM1, must be involved to avoid the fractures of constituent components in the joint area.

In the second application, a full atomistic molecular dynamics (MD) computation approach has been employed to quantify the Flory-Huggins parameters between poly(lactic acid) (PLA), poly(glycolic acid) (PGA), and tetracycline-HCl (TC-HCl) drugs, which can elucidate the thermodynamic stability and the interaction between drugs and poly(lactic/glycolic acid) (PLGA) carriers polymers. Thermodynamic analysis regarding the miscibility and the stability of PLA, PGA, TC-HCl phases are then conducted in line with the experimental fabrication of polymer-drug films of two different copolymer ratio products, i.e., 50/50 (PLA/PGA ratio) and 75/25 PLGA samples. Meso-scale computations using phase-field method (PFM) are also conducted to predict the structural evolution of PLGA/TC-HCl systems using the calculated Flory-Huggins parameters. The results show that the surface morphology of PLGA/TC-HCl film can be highly dependent upon the thermodynamic interaction between the polymer and drug phases.

In the third application, full atomistic MD simulations have been performed on tetra-sulfides and undoped conjugated polymers pernigraniline base polyaniline (PNB), leucoemeraldine base polyaniline (LEB), poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPY) to investigate the binding effectiveness between polysulfides and polymer binders. The weight ratio between sulfur and binder in lithium{sulfur cells is considered in 1:1 v/v mixture of dioxolane/dimethoxyethane. The simulations reveal that the end group 2 of PNB can effectively bind a lithium tetra-sulfide (i.e. Li2S4) cluster or 2 out of 43 Li2S4 molecules with the effect of solvent. However, repeat units of PNB, LEB, PEDOT and PPY seem ineffective in binding solvated Li2S4 through non-bonded interaction, especially when the concentration of tetra-sulfide/binder in a local domain of the cathode is low. Therefore, polymers with this specific functional group (i.e. the end group 2 of PNB) are suggested to be further studied as potential effective binders to inhibit the shuttle effect of solvated lithium polysulfides. Also, since the solvent has considerable impact on the binding effectiveness between tetra-sulfides and binder, it is suggested to take advantage of the explicit solvation models, such as those built in this work, to predict how other influencing factors affect binding between polysulfides and polymers.

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