Publications

Abstract not provided.

Abstract not provided.

The band structure and electronic properties in a series of vinylene-linked heterocyclic conducting polymers are investigated using density functional theory (DFT). In order to accurately calculate electronic band gaps, we utilize hybrid functionals with fully periodic boundary conditions to understand the effect of chemical functionalization on the electronic structure of these materials. The use of predictive first-principles calculations coupled with simple chemical arguments highlights the critical role that aromaticity plays in obtaining a low band gap polymer. Contrary to some approaches which erroneously attempt to lower the band gap by increasing the aromaticity of the polymer backbone, we show that being aromatic (or quinoidal) in itself does not ensure a low band gap. Rather, an iterative approach which destabilizes the ground state of the parent polymer toward the aromatic ↔ quinoidal level crossing on the potential energy surface is a more effective way of lowering the band gap in these conjugated systems. Our results highlight the use of predictive calculations guided by rational chemical intuition for designing low band gap polymers in photovoltaic materials. © 2011 American Chemical Society.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Complex metal hydrides continue to be investigated as solid-materials for hydrogen storage. Traditional interstitial metal hydrides offer favorable thermodynamics and kinetics for hydrogen release but do not meet energy density requires. Anionic metal hydrides, and complex metal hydrides like magnesium borohydride have higher energy densities compared to interstitial metal hydrides, but poor kinetics and/or thermodynamically unfavorable side products limit their deployment as hydrogen storage materials in transportation applications. Main-group anionic materials such as the bis(borane)hypophosphite salt [PH2(BH3)2] have been known for decades, but only recently have we begun to explore their ability to release hydrogen. We have developed a new procedure for synthesizing the lithium and sodium hypophosphite salts. Routes for accessing other metal bis(borane)hypophosphite salts will be discussed. A significant advantage of this class of material is the air and water stability of the anion. Compared to metal borohydrides, which reactive violently with water, these phosphorus-based salts can be dissolved in protic solvents, including water, with little to no decomposition over the course of multiple days. The ability of these salts to release hydrogen upon heating has been assessed. While preliminary results indicate phosphine and boron-containing species are released, hydrogen is also a major component of the volatile species observed during the thermal decomposition. Additives such as NaH or KH mixed with the sodium salt Na[PH2(BH3)2] significantly perturb the decomposition reaction and greatly increase the mass loss as determined by thermal gravimetric analysis (TGA). This symbiotic behavior has the potential to affect the hydrogen storage ability of bis(borane)hypophosphite salts.

The controlled self-assembly of polymer thin-films into ordered domains has attracted significant academic and industrial interest. Most work has focused on controlling domain size and morphology through modification of the polymer block-lengths, n, and the Flory-Huggins interaction parameter, {chi}. Models, such as Self-Consistent Field Theory (SCFT), have been successful in describing the experimentally observed morphology of phase-separated polymers. We have developed a computational method which uses SCFT calculations as a predictive tool in order to guide our polymer synthesis. Armed with this capability, we have the ability to select {chi} and then search for an ideal value of n such that a desired morphology is the most thermodynamically favorable. This approach enables us to synthesize new block-polymers with the exactly segment lengths that will undergo self-assembly to the desired morphology. As proof-of-principle we have used our model to predict the gyroidal domain for various block lengths using a fixed {chi} value. To validate our computational model, we have synthesized a series of block-copolymers in which only the total molecular length changes. All of these materials have a predicted thermodynamically favorable gyroidal morphology based on the results of our SCFT calculations. Thin-films of these polymers are cast and annealed in order to equilibrate the structure. Final characterization of the polymer thin-film morphology has been performed. The accuracy of our calculations compared to experimental results is discussed. Extension of this predictive ability to tri-block polymer systems and the implications to making functionalizable nanoporous membranes will be discussed.

A rational approach was used to design polymeric materials for thin-film electronics applications, whereby theoretical modeling was used to determine synthetic targets. Time-dependent density functional theory calculations were used as a tool to predict the electrical properties of conjugated polymer systems. From these results, polymers with desirable energy levels and band-gaps were designed and synthesized. Measurements of optoelectronic properties were performed on the synthesized polymers and the results were compared to those of the theoretical model. From this work, the efficacy of the model was evaluated and new target polymers were identified.

This paper describes mitigation technologies that are intended to enable the deployment of advanced hydrogen storage technologies for early market and automotive fuel cell applications. Solid State hydrogen storage materials provide an opportunity for a dramatic increase in gravimetric and volumetric energy storage density. Systems and technologies based on the advanced materials have been developed and demonstrated within the laboratory [1,2], and in some cases, integrated with fuel cell systems. The R&D community will continue to develop these technologies for an ever increasing market of fuel cell technologies, including, forklift, light-cart, APU, and automotive systems. Solid state hydrogen storage materials are designed and developed to readily release, and in some cases, react with diatomic hydrogen. This favorable behavior is often accomplished with morphology design (high surface area), catalytic additives (titanium for example), and high purity metals (such as aluminum, Lanthanum, or alkali metals). These favorable hydrogen reaction characteristics often have a related, yet less-desirable effect: sensitivity and reactivity during exposure to ambient contamination and out-of-design environmental conditions. Accident scenarios resulting in this less-favorable reaction behavior must also be managed by the system developer to enable technology deployment and market acceptance. Two important accident scenarios are identified through hazards and risk analysis methods. The first involves a breach in plumbing or tank resulting from a collision. The possible consequence of this scenario is analyzed though experimentally based chemical kinetic and transport modeling of metal hydride beds. An advancing reaction front between the metal hydride and ambient air is observed to proceed throughout the bed. This exothermic reaction front can result in loss of structural integrity of the containing vessel and lead to un-favorable overheating events. The second important accident scenario considered is a pool fire or impinging fire resulting from a collision between a hydrocarbon or hydrogen fueled vehicle. The possible consequence of this scenario is analyzed with experimentally-based numerical simulation of a metal hydride system. During a fire scenario, the hydrogen storage material will rapidly decompose and release hydrogen at high pressure. Accident scenarios initiated by a vehicular collision leading a pipe break or catastrophic failure of the hydride vessel and by external pool fire with flame engulfing the storage vessel are developed using probabilistic modeling. The chronology of events occurring subsequent to each accident initiator is detailed in the probabilistic models. Technology developed to manage these scenarios includes: (1) the use of polymer supports to reduce the extent and rate of reaction with air and water, (2) thermal radiation shielding. The polymer supported materials are demonstrated to provide mitigation of unwanted reaction while not impacting the hydrogen storage performance of the material. To mitigate the consequence of fire engulfment or impingement, thermal radiation shielding is considered to slow the rate of decomposition and delay the potential for loss-of-containment. In this paper we explore the use of these important mitigation technologies for a variety of accident scenarios.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.