Computational Materials Science and Engineering: Model Development and Case Study

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

Conducting polymers and hybrid materials for technological applications

Depletion of natural resources and non-renewable energy sources has recently accelerated due to the development of globalized economy and industrialization. During the last years, the scientific community has devoted much of its efforts to developing and improving renewable energy sources. In this context, electrochemical capacitors, or supercapacitors, have received great interest owing to their properties and potential applications. Supercapacitors and their different components constitute the main line of work of the present thesis. More specifically the thesis investigates the use of hydrogels in various distinct functions. The work done in the thesis has been developed both experimentally and corroborated by theoretical studies based on quantum mechanics and molecular dynamics. The main body of the thesis is divided into three parts. The first one includes the synthesis and characterization of a hydrogel derived from an unsaturated polyesteramide as a solid electrolyte in a supercapacitor. This part consists of the electrochemical characterization of the hydrogel obtained, evaluating the performance of the hydrogel when acting as a solid electrolyte, as well as a study of ion diffusion through the hydrogel carried out with molecular dynamics. These studies allow to obtain the optimal conditions for the synthesis and use of this hydrogel. The second part is based on the preparation and characterization of a multilayer system as an electrode in a supercapacitor. More specifically, it covers the preparation of a multilayer system consisting of PVA and the conductive polymer PEDOT, prepared by a layer-by-layer process. The chapter also consists of a theoretical study of quantum mechanics in which the movement and changes of a PEDOT monolayer are studied, and allows to elucidate the mechanisms and electronic properties that had not been fully understood at the experimental level. Finally, the third and last part incorporates the preparation of a multifunctional system consisting entirely of hydrogels. The chapter begins by detailing the preparation of an electrode of a supercapacitor based on a PEDOT hydrogel and alginate. After its characterization as an electrode, other functionalities that can be given to this system are explored. Among them, a reusable and recyclable pressure sensor is prepared to detect pressure changes linearly and with great sensitivity, as well as a controlled drug release system, in particular a controlled release by electrical stimulation of curcumin.Degut al desenvolupament de l'economia globalitzada i la industrialització, s'ha accelerat l'esgotament de recursos naturals i fonts d'energia no renovables. En els últims anys, la comunitat científica ha dedicat una gran part dels seus esforços a desenvolupar i millorar les fonts d'energia renovable. En aquest context, els capacitors electroquímics, o supercapacitors, han rebut un gran interès degut a les seves propietats i potencials aplicacions. El principal camp de treball d'aquesta tesis són els supercapacitors i les diferents parts que els constitueixen, més concretament la tesis estudia l'ús d'hidrogels en diverses funcions diferents. El treball fet a la tesis s'ha desenvolupat tant a nivell experimental com corroborat mitjançant estudis teòrics basats en la mecànica quàntica i la dinàmica molecular. El cos principal de la tesis està dividit en 3 parts. La primera part inclou la síntesis i caracterització d'un hidrogel derivat d'una poliesteramida insaturada com a electròlit sòlid en un supercapacitor. Aquesta part consta de la caracterització electroquímica de l'hidrogel obtingut, avaluant el rendiment de l'hidrogel a l'hora d'actuar com un electròlic sòlid, així com també consta d'un estudi de difusió dels ions a través d¿aquest dut a terme amb dinàmica molecular. Aquests estudis permeten obtenir les condicions òptimes per la síntesis i ús d'aquest hidrogel. La segona part està dedicada a la preparació i caracterització d'un sistema multicapa com a elèctrode en un supercapacitor. Més concretament, es basa en la preparació d'un sistema multicapa format per PVA i el polímer conductor PEDOT, preparat mitjançant un procés capa per capa. El capítol consta també d'un estudi teòric de mecànica quàntica en el que s'estudia el moviment i canvis d'una monocapa de PEDOT, i permet elucidar els mecanismes i propietats electròniques que no s'havien entès completament a nivell experimental. Finalment, l'última part es tracta de la preparació d'un sistema multifuncional format completament per hidrogels. El capítol comença detallant la preparació d'un elèctrode d'un supercapacitor basat en un hidrogel de PEDOT i alginat. Després de la seva caracterització com a elèctrode, s'exploren les altres funcionalitats que se li poden donar a aquest sistema. Es prepara un sensor de pressió reutilitzable i reciclable que permet detectar canvis de pressió linealment i amb una gran sensibilitat, i també es prepara un sistema d'alliberament controlat de fàrmacs, concretament l'alliberament controlat mitjançant estímul elèctric de curcuminaPostprint (published version

Developmet of flexible electrodes and lightweight capacitors

This work has focused on the study and development of hierarchically, flexible electrodes and lightweight capacitor using as a source of flexibility. the y-polyglutamic acid (y-PGA) and as an electroactive polymer the poly(3,4-ethylenedioxythiophene) (PEDOT) in composite with alumina (Al2O3),Initially, the PEDOT/Al2O3 composite electroactive film was studied under different monomers: clay proportion and considering the amphoteric behavior of the Al2O3, the analysis of the pH affectation was done. Further, the multi-step in situ polymerization was studied. The experiments demonstrated that the 4:1 monomer: Al2O3 proportion, the multi-step basic medium (pH 8.8) (due to the proximity to the isoelectric point of the filler) favors the electrochemical properties with respect to pure PEDOT. The aforementioned variables combination displays an increment of 55% in specific capacitance (SC) (141 F g-1) compared to the pristine PEDOT. The values obtained demonstrate the synergetic effect of all the variables mentioned and the participation of the filler as a secondary doping agent facilitating the ion mobility.Secondly, the assembly and development of lightweight electrodes was achieved based on the supramolecular incorporation of PEDOT particles into an aqueous biohydrogel (y-PGA). Subsequently, a 20% w/w PEDOT particles were dispersed to give the electroactive characteristic to the gel, following by an extra step of in situ electropolymerization of poly(hydroxymethyl-3,4- ethylenedioxythiophene) (PHMeDOT) to join and increase the conductive polymer connections. Results revealed that electrochemical performance depends of the polymerization time, in this case, the optimum results obtained was the 7h polimerization electrode with a SC 45.4 ±0.7 mF cm-2 from cyclic voltammetry (CV) and charge-discharge (GCD) long-term stability. Finally, the applicability in lightweight and flexible energy-harvesting systems was verified by the LED bulb test. As a third step, a new solid organic symmetric capacitor was constructed, mingling the best results obtained from the previous studies as discussed. Two self-supported p-doped electrodes of y-PGA, PEDOT microparticles, PHMeDOT (2h electropolymerization) with filler of Al2O3 were produced. The electrodes were joined to a supporting solid ¿-PGA electrolyte doped with NaHCO3 salt from the synthesis step and functioning later as the electrolyte The electrochemical performance suggested an excellent prototype stability after 2000 charge-discharge cycles evidencing through an only 8% SC loss, evidencing an excellent stability.This thesis also focused in the n-doped PEDOT-polycation ionene electrode development. As a first step, a synthetic electrochemical protocol was followed to produce an n-doped PEDOT using macromolecular dopant agent, specifically, 1,4- diazabicyclo[2.2.2]octane-based ionene bearing N,N’-(meta-phenylene)dibenzamide linkages (mPi) was established. The protocol consisted of a three-step process , individually optimized: (1) preparation of p-doped (oxidized) PEDOT at a constant potential of +1.40 V in acetonitrile with LiClO4 as electrolyte; (2) dedoping of oxidized PEDOT using a fixed potential of –1.30 V in water; and (3) redoping of dedoped PEDOT applying a reduction potential of –1.10 V in water with mPI. The results obtained displayed a comparable doping level with respect tothe doping level obtained in case of TMA. Nevertheless, the PEDOT doped with mPi revealed better thermal stability and hydrophilicity than the former pristine p-doped and dedoped PEDOT. The final work, considers the influence of the ionene topology on the properties of n-doped PEDOT by comparing three isomeric topomers. The highest doping level was obtained for the para-isomeric ionene-containing electrode, even though the content of ortho- and meta-topomers into the corresponding ndoped PEDOT:ionene electrodes is greater , the topomers interactions as well were related with the hydrogelation of the ionenes.Este trabajo se ha centrado en el estudio jerárquico y desarrollo de electrodos flexibles y condensadores livianos utilizando como fuente de flexibilidad. el ácido ¿-poliglutámico (¿-PGA) y como polímero electroactivo el poli (3,4-etilendioxitiofeno) (PEDOT) en compuesto con alúmina (Al2O3), Inicialmente, la película electroactiva compuesta PEDOT / Al2O3 se estudi ó bajo diferentes proporciones de monómeros:Al2O3 y considerando el comportamiento anfótero del Al2O3, se realizó el análisis de la afectación del pH. Los experimentos demostraron que la proporción 4: 1, multicapa en medio básico (pH 8,8) (debido a la proximidad al punto isoeléctrico de la carga) favorece las propiedades electroquímicas con respecto al PEDOT puro. La combinación de las variables antes mencionadas resultan en un incremento de 55% de la capacitancia espec ífica (SC) (141 F g-1) en comparación con el PEDOT, por sí mismo. Los valores obtenidos demuestran el efecto sinérgico de todas las variables mencionadas y la participación del filler como agente dopante secundario facilitando la movilidad i ónica. En segundo lugar, el ensamblaje y desarrollo de electrodos ligeros se logr ó en base a la incorporación supramolecular de partículas de PEDOT en un bio-hidrogel acuoso (¿-PGA). Posteriormente, se dispersaron partículas de PEDOT al 20% m / m confiriendo la característica electroactiva al gel, seguido de una etapa adicional de electropolimerizaci ón in situ de poli (hidroximetil-3,4-etilendioxitiofeno) (PHMeDOT) para establecer conexiones entre las partículas de PEDOT e incrementar la conductividad. Los resultados indicaron que el rendimiento electroquímico depende del tiempo de polimerizaci ón, en este caso, los resultados óptimos obtenidos fue para el electrodo polimerizado 7h con un SC 45.4 ± 0.7 mF cm-2 de voltametría cíclica (CV) y mostrando una alta electro estabilidad. Finalmente, la aplicabilidad en sistemas ligeros y flexibles de almacenamiento de energía fue verificada con la prueba de la bombilla LED. Como tercer paso, se construyó un nuevo condensador simétrico orgánico sólido, basados en el know-how desarrollado de los estudios previos. Se produjeron dos electrodos p-dopados auto-soportados de ¿-PGA, micropartículas PEDOT, PHMeDOT (electropolimerización 2h) con relleno de Al2O3. Los electrodos se unieron a un electrolito de ¿-PGA sólido dopado con sal de NaHCO3 desde la etapa de s íntesis. El rendimiento electroquímico sugirió una excelente estabilidad del prototipo después de 2000 ciclos de carga y descarga, con s ólo una pérdida de SC del 8%. Esta tesis también se centró en el desarrollo del electrodo de ioneno - polietileno PEDOT n-dopado. Como primer paso, se siguió un protocolo de síntesis electroquímica para producir un PEDOT n-dopado utilizando un agente dopante macromolecular, específicamente, ioneno basado en 1,4-diazabiciclo [2.2.2] octano con N, N '- (meta-fenileno) dibenzamida (mPi). El protocolo consistió en un proceso de tres pasos, optimizados individualmente: (1) preparaci ón de PEDOT pdopado (oxidado) a un potencial constante de +1.40 V en acetonitrilo con LiClO4 como electrolito;(2) desdopadp de PEDOT oxidado utilizando un potencial fijo de -1,30 V en agua; y (3) redopado del PEDOT desdopado aplicando un potencial de reducción de -1.10 V en agua con mPI. Los resultados obtenidos muestran un nivel de dopaje comparable con respecto al nivel de dopaje obtenido en el caso de TMA. Sin embargo, el PEDOT dopado con mPi revel ó una mejor estabilidad térmica e hidrofilicidad que el antiguo PEDOT p-dopado y el desdopado . El trabajo final, considera la influencia de la topolog ía ioneno en las propiedades de PEDOT n-dopado mediante la comparaci ón de tres topómeros isoméricos.El nivel más alto de dopaje se obtuvo para el electrodo que contiene ioneno para-isomérico, aunque el contenido de orto y meta en los correspondientes electrodos de PEDOT: ioneno es mayor, las interacciones topoméricas también se relacionaron con la formación de gelPostprint (published version

Nanomechanical coupling of mechanomutable polyelectrolytes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 255-282).Nanotechnology has advanced to the point where almost any molecular functional group can be introduced into a composite material system. However, emergent properties attained via the combination of arbitrary components - e.g., the complexation of two weak polyelectrolytes - is not yet predictive, and thus cannot be rationally engineered. Predictive and reliable quantification of material properties across scales is necessary to enable the design and development of advanced functional (and complex) materials. There is a vast amount of experimental study which characterize the strength of electrostatic interactions, topology, and viscoelastic properties of polyelectrolyte multilayers (PEMs), but very little is known about the fundamental molecular interactions that drive system behavior. Here, we focus on two specific weak polyelectrolytes - poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) - that undergo electrostatic complexation, and can be manipulated as function of pH. While the driving mechanism investigated here is ionic interactions, the findings and atomistic approaches are applicable to a variety of systems such as hydrogen bonded polypeptides (e.g., protein structures), as well as similar polyelectrolyte systems (e.g., PSS, PDMA, etc.). Specifically, in this dissertation, the coupling of electrostatic cross-links and weak interactions, polyelectrolyte persistence length and molecular rigidity of PAA and PAH is investigated with full atomistic precision. Large-scale molecular dynamics (MD) simulations indicate the stiffening of PEMs cannot be explained by increased electrostatic cross-linking alone, but rather the effect is amplified by the increase in molecular rigidity due to self-repulsion. Based on MD simulations, a general theoretical model for effective electrostatic persistence length is proposed for highly flexible polyelectrolytes and charged macromolecules through the introduction of an electrostatic contour length which can applied to other chemical species. A focus on adhesion reveals the effective cross-linking strength exceeds the strength of ionic interaction alone, due to secondary effects (e.g., H-bonding, steric effects, etc.) Moreover, a derived elastic model for complexation reveals a critical bound for cross-link density and stiffness, indicating the required conditions to induce cooperative mechanical behavior. The key insight is that these critical conditions can be further extended for the coupling of flexible molecules in general, such as proteins or flexible nanoribbons. The results demonstrate how nanoscale control can lead to uniquely tunable mechanomutable materials from designed functional building blocks. While PEM systems are currently being developed for biosensor, membrane, and tissue engineering technologies, the results presented herein provide a basis to tune the properties of such systems at the nanoscale, thereby engineering system behavior and performance across scales. Understanding the bounds of mechanical performance of two specific polyelectrolyte species, and their joint interaction through complexation, provides a basis for coupling molecules with various functionalities. Similar to complete understanding the limitations of a steel beam in construction of a bridge, the systematic delineation of polyelectrolyte complexation allows quantitative prediction of larger-scale systems.by Steven W. Cranford.Ph.D