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Membranes made of stacked layers of graphene oxide (GO) hold the tantalizing promise of revolutionizing desalination and water filtration if selective transport of molecules can be controlled. We present the findings of an integrated study that combines experiment and molecular dynamics simulation of water intercalated between GO layers. We simulated a range of hydration levels from 1 wt.% to 23.3 wt.% water. The interlayer spacing increased upon hydration from 0.8 nm to 1.1 nm. We also synthesized GO membranes that showed an increase in layer spacing from about 0.7 nm to 0.8 nm and an increase in mass of about 15% on hydration. Water diffusion through GO layers is an order of magnitude slower than that in bulk water, because of strong hydrogen bonded interactions. Most of the water molecules are bound to OH groups even at the highest hydration level. We observed large water clusters that could span graphitic regions, oxidized regions and holes that have been experimentally observed in GO. Slow interlayer diffusion can be consistent with experimentally observed water transport in GO if holes lead to a shorter path length than previously assumed and sorption serves as a key rate-limiting step.

Vehicle lightweighting is a promising strategy that can reduce energy consumption and GHG emissions without compromising vehicle’s performance or size. The cost of lightweighting plays a critical role in determining the adoption of lightweighting technologies by consumers and manufacturers among advanced vehicle technologies. This analysis estimates the cost of lightweighting needed to achieve significant light-duty vehicle adoption to provide reductions in use-phase GHG emissions. Three different costs of lightweighting scenarios in the U.S. market including a baseline scenario, advanced technology scenario, and widespread scenario are evaluated employing Automotive Deployment Options Projection Tool (ADOPT) in conjunction with other technology improvement assumptions (e.g., advancements in fuel and battery technologies, and material price reductions) from DOE. ADOPT leverages a database of over 700 existing vehicle models and options, enabling it to provide a high degree of realism and capture the unique characteristics of popular vehicles and the endogenously evolvement of the vehicle options. For baseline scenario, the use-phase GHG emissions are reduced by more than 50% and lightweighting fraction reaches 15% by 2046 compared to 2015 levels. The widespread scenario further reduces the GHG emissions by about 4% from the additional 10% glider mass reduction compared to the baseline scenario. The benefit came largely from lightweighting being implemented in the large market segment of lower-price vehicles, due to the relatively low lightweighting cost ($5/kg).

A polyethersulfone (PES)-supported graphene oxide (GO) membrane has been developed by a simple casting approach. This stable membrane is applied for ethanol/water separation at different temperatures. The 5.0 µm thick GO film coated on PES support membrane showed a long-term stability over a testing period of one month and excellent water/ethanol selectivity at elevated temperatures. The water/ethanol selectivity is dependent on ethanol weight percentage in water/ethanol feed mixtures and on operating temperature. The water/ethanol selectivity was enhanced with an increase of ethanol weight percentage in water/ethanol mixtures, from below 100 at RT to close to 874 at a 90 °C for 90% ethanol/10% water mixture. Molecular dynamics simulation of water-ethanol mixtures in graphene bilayers, that are considered to play a key role in transport, revealed that molecular transport is negligible for layer spacing below 1 nm. The differences in the diffusion of ethanol and water in the bilayer are not consistent with the large selectivity value experimentally observed. The entry of water and ethanol into the interlayer space may be the crucial step controlling the selectivity.

Graphene oxide (GO) is a promising membrane system for chemical separation applications due to its 2-D nanofluidics properties and an ability to control interplanar spacing for selectivity. The permeance of water, methanol (MeOH) and isopropyl alcohol (IPA) through 5 µm thick membranes was found to be 0.38 ± 0.15, 0.33 ± 0.16 and 0.42 ± 0.31 LMH/bar (liter/m2·h·bar), respectively. Interestingly, the permeance of a water–alcohol mixture was found to be dramatically lower (~0.01 LMH/bar) than any of its components. Upon removing the solvent mixture, the transmembrane flux of the pure solvent was recovered to near the original permeance. The interlayer space of a dried GO membrane was found to be 8.52 Å, which increased to 12.19 Å. 13.26 Å and 16.20 Å upon addition of water, MeOH and IPA. A decrease in d-space, about 2 Å, was consistently observed when adding alcohol to water wetted GO membrane and an optical color change and reduction in permeance. A newly proposed mechanism of a partial reduction of GO through a catalytic reaction with the water–alcohol mixture is consistent with experimental observations.

Three water adsorption–desorption mechanisms are common in inorganic materials: chemisorption, which can lead to the modification of the first coordination sphere; simple adsorption, which is reversible; and condensation, which is irreversible. Regardless of the sorption mechanism, all known materials exhibit an isotherm in which the quantity of water adsorbed increases with an increase in relative humidity. Here, we show that carbon-based rods can adsorb water at low humidity and spontaneously expel about half of the adsorbed water when the relative humidity exceeds a 50–80% threshold. The water expulsion is reversible, and is attributed to the interfacial forces between the confined rod surfaces. At wide rod spacings, a monolayer of water can form on the surface of the carbon-based rods, which subsequently leads to condensation in the confined space between adjacent rods. As the relative humidity increases, adjacent rods (confining surfaces) in the bundles are drawn closer together via capillary forces. At high relative humidity, and once the size of the confining surfaces has decreased to a critical length, a surface-induced evaporation phenomenon known as solvent cavitation occurs and water that had condensed inside the confined area is released as a vapour. Carbon-based rods can adsorb water at low humidity and release it at high humidity through a reversible physical process that is associated with the dynamic spacing between rods.

Vehicle lightweighting is a promising strategy that can reduce energy consumption and GHG emissions without compromising vehicle's performance or size. The cost of lightweighting plays a critical role in determining the adoption of lightweighting technologies by consumers and manufacturers among advanced vehicle technologies. This analysis estimates the cost of lightweighting needed to achieve significant light-duty vehicle adoption to provide reductions in use-phase GHG emissions. Three different costs of lightweighting scenarios in the U.S. market including a baseline scenario, advanced technology scenario, and widespread scenario are evaluated employing Automotive Deployment Options Projection Tool (ADOPT) in conjunction with other technology improvement assumptions (e.g., advancements in fuel and battery technologies, and material price reductions) from DOE. ADOPT leverages a database of over 700 existing vehicle models and options, enabling it to provide a high degree of realism and capture the unique characteristics of popular vehicles and the endogenously evolvement of the vehicle options. For baseline scenario, the use-phase GHG emissions are reduced by more than 50% and lightweighting fraction reaches 15% by 2046 compared to 2015 levels. The widespread scenario further reduces the GHG emissions by about 4% from the additional 10% glider mass reduction compared to the baseline scenario. The benefit came largely from lightweighting being implemented in the large market segment of lower-price vehicles, due to the relatively low lightweighting cost (5/kg).

Fuel cell vehicles are entering the automotive market with significant potential benefits to reduce harmful greenhouse emissions, facilitate energy security, and increase vehicle efficiency while providing customer expected driving range and fill times when compared to conventional vehicles. One of the challenges for successful commercialization of fuel cell vehicles is transitioning the on-board fuel system from liquid gasoline to compressed hydrogen gas. Storing high pressurized hydrogen requires a specialized structural pressure vessel, significantly different in function, size, and construction from a gasoline container. In comparison to a gasoline tank at near ambient pressures, OEMs have aligned to a nominal working pressure of 700 bar for hydrogen tanks in order to achieve the customer expected driving range of 300 miles. Beyond the need to contain pressure, the hydrogen tanks also differ from gasoline fuel tanks because of the additional vehicle space needed due to the lower hydrogen energy volumetric density even with the highly efficient fuel cell (four times the external volume of a gasoline tank including the fuel cell efficiency benefit). The main difference and challenge of hydrogen tanks is the construction and design that depends on a high utilization of carbon fiber in order to reduce the weight of the pressure vessel although substantially increasing the cost. In 2012, the U.S. Department of Energy (DOE), Office of Fuel Cell Technologies recognized these challenges and initiated a project to research enhance materials and design parameters to reduce the cost of hydrogen storage tanks. The project was led by Pacific Northwest National Lab (PNNL) and involved several other organizations in the value chain of hydrogen tank development: AOC, Ford Motor Company, Hexagon Lincoln, and Toray CFA. The project took a holistic approach to improving performance by investigating: (1) composite matrix resin alternatives including adding nano-reinforcing particles and fiber-matrix sizing for improved adhesion, (2) carbon fiber alternatives, (3) tank design alternatives using hybrid fiber layups, and (4) opportunities with cold gas operating conditions to maintain the hydrogen density while reducing the tank composite utilization. In each of these areas, the project successfully identified the potential benefits: (1) demonstrated new resin with 50% cost reduction at equivalent or better performance than traditional epoxy, (2) identified 4% to 12% improvement with fiber alternatives, (3) developed validated tank design models with improved failure prediction capability, and (4) confirmed value and system level viability of cold gas storage with a combined 22% cost reduction opportunity. This paper examines these modifications and considers the outlook for on-board 700 bar compressed hydrogen tank systems to achieve the commercialization goals for fuel cell vehicles.

Recently, the quaternary III–V material system gallium indium nitride arsenide (GaInNAs) has attracted a great deal of attention for optoelectronic devices such as lasers, photodetectors, and solar cells. However, growth of these materials is complicated by the difficulty of providing reactive nitrogen and getting the nitrogen to incorporate into the crystal lattice. This dissertation reports on the growth of GaInNAs by molecular beam epitaxy at The University of Texas at Austin. This MBE system uses a radio-frequency plasma with a novel inert gas dilution technique to produce controllable amounts of active nitrogen to the growth surface. Using this technique, a variety of GaNAs and GaInNAs photodetectors have been grown. We report the first GaNAs avalanche photodiode grown on GaAs, with a quantum efficiency of 27% at 1.06μm and a peak bandwidth of 27GHz. We have also grown resonant cavity avalanche photodiodes operating at 1.06μm with 60% quantum efficiency.

Understanding the viscoelastic properties of living cells and their relation to cell state and morphology remains challenging. Low-frequency mechanical perturbations have contributed considerably to the understanding, yet higher frequencies promise to elucidate the link between cellular and molecular properties, such as polymer relaxation and monomer reaction kinetics. Here, we introduce an assay, that uses an actuated microcantilever to confine a single, rounded cell on a second microcantilever, which measures the cell mechanical response across a continuous frequency range ≈ 1–40 kHz. Cell mass measurements and optical microscopy are co-implemented. The fast, high-frequency measurements are applied to rheologically monitor cellular stiffening. We find that the rheology of rounded HeLa cells obeys a cytoskeleton-dependent power-law, similar to spread cells. Cell size and viscoelasticity are uncorrelated, which contrasts an assumption based on the Laplace law. Together with the presented theory of mechanical de-embedding, our assay is generally applicable to other rheological experiments. While rheology studies have contributed to the understanding of the viscoelastic properties of living cells, the use of higher frequencies promises elucidate the link between cellular and molecular properties. Here authors introduce a rheological assay that measures the cell mechanical response across a continuous frequency range ≈ 1 – 40 kHz.