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Stephen J. Harley

Bio: Stephen J. Harley is an academic researcher from Lawrence Livermore National Laboratory. The author has contributed to research in topics: Sorption & Wine. The author has an hindex of 12, co-authored 33 publications receiving 419 citations. Previous affiliations of Stephen J. Harley include University of California, Davis & University of California.
Topics: Sorption, Wine, Adsorption, Bottle, Langmuir

Papers
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TL;DR: The results demonstrate that moisture is able to penetrate the material over a range of temperatures and humidities and quantitatively assesses how water vapor diffuses and ad/absorbs into polymeric materials that are traditionally considered hydrophobic.
Abstract: The dynamic and equilibrium water vapor sorption properties of Sylgard-184, a commercially available poly(dimethylsiloxane) elastomer (PDMS), were determined via gravimetric analysis from 30 to 70 °C. Described here is a methodology for quantitatively assessing how water vapor diffuses and ad/absorbs into polymeric materials that are traditionally considered hydrophobic. PDMS materials are frequently chosen for their moisture barrier properties; our results, however, demonstrate that moisture is able to penetrate the material over a range of temperatures and humidities. The sorption values measured here ranged from ca. 0.1 to 1.4 cm3 (STP) H2O/g Sylgard. The isotherms exhibited sigmoidal character and were fit to a triple mode sorption model. Asymptotic behavior at low water activities was characterized using a Langmuir type adsorption model, linear behavior was fit to a Henry’s law type dependence, and the convex portion at higher activities was fit with good agreement to Park’s equation for pooling or c...

64 citations

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TL;DR: Microscopy, scattering, spectroscopic, thermal, and dielectric techniques show that the covalent inclusion of the cross-linking particles restricts microphase separation, inhibits the formation of hard-block domains, and decelerates the motional dynamics of the polyurethane backbone.
Abstract: Octa-OH-functional POSS has been incorporated into a model polyurethane elastomer as a comparatively massive and notionally “robust” 3-dimensional cross-linking core. The effects of this cross-linking moiety on the morphology and molecular dynamics of the system are studied over a range of size and time scales. Microscopy, scattering, spectroscopic, thermal, and dielectric techniques, in agreement with each other, show that the covalent inclusion of the cross-linking particles restricts microphase separation, inhibits the formation of hard-block domains, and decelerates the motional dynamics of the polyurethane backbone. The effects on both the morphology and the dynamics of the polyurethane system are not continuous but occur in a steplike manner in the loading region of 4–6 wt % POSS. This critical region is thought to correspond to a sterically induced transition from one dominant morphology (microphase segregated) to an increasingly homogeneous nanophase segregated domain morphology. Contrary to expec...

55 citations

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TL;DR: In this article, bromine oxidation of porous silicon nanoparticles followed by reaction with n-butyllithium was shown to be stable in air and water indefinitely, and a combination of infrared, ultraviolet/visible, and photoluminescence demonstrated the presence of small crystalline silicon particles and saturated hydrocarbon ligands, while solid and liquid-state nuclear magnetic resonance spectroscopies established that butyl ligands are localized on the nanocrystal surface.
Abstract: Air- and water-stable silicon nanocrystals were prepared by the bromine oxidation of porous silicon nanoparticles followed by reaction with n-butyllithium. Transmission electron microscopy suggests that the vigorous oxidation of porous silicon under reflux conditions removes the porous layer from the nanoparticle to expose a crystalline silicon core that can be passivated with organic ligands. A combination of infrared, ultraviolet/visible, and photoluminescence demonstrate the presence of small crystalline silicon particles and saturated hydrocarbon ligands, while solid- and liquid-state nuclear magnetic resonance spectroscopies establish that butyl ligands are localized on the nanocrystal surface. All of these analytical methods suggest that the product of this synthesis is stable in air and water indefinitely.

54 citations

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TL;DR: The exchange rates of water ligated to Co(II) atoms in two polyoxotungstate sandwich molecules using the (17)O-NMR-based Swift-Connick method are reported and the molecules are clearly stable and monospecific in slightly acidic solutions, but dissociate in strongly acidic solutions.
Abstract: Polyoxometalate ions are used as ligands in water-oxidation processes related to solar energy production. An important step in these reactions is the association and dissociation of water from the ...

52 citations

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TL;DR: Water uptake in silica-filled and unfilled poly(dimethylsiloxane) networks is investigated; however, the model is versatile enough to be used with a wide range of materials and vapors.
Abstract: A high-fidelity model of kinetic and equilibrium sorption and diffusion is developed and exercised. The gas-diffusion model is coupled with a triple-sorption mechanism: Henry’s law absorption, Langmuir adsorption, and pooling or clustering of molecules at higher partial pressures. Sorption experiments are conducted and span a range of relative humidities (0–95 %) and temperatures (30–60 °C). Kinetic and equilibrium sorption properties and effective diffusivity are determined by minimizing the absolute difference between measured and modeled uptakes. Uncertainty quantification and sensitivity analysis methods are described and exercised herein to demonstrate the capability of this modeling approach. Water uptake in silica-filled and unfilled poly(dimethylsiloxane) networks is investigated; however, the model is versatile enough to be used with a wide range of materials and vapors.

21 citations


Cited by
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TL;DR: It is suggested that future advances in solar fuels science will be accelerated by the development of new methods for materials synthesis and characterization, along with in-depth investigations of redox mechanisms at catalytic surfaces.
Abstract: Water oxidation is a key chemical transformation for the conversion of solar energy into chemical fuels Our review focuses on recent work on robust earth-abundant heterogeneous catalysts for the oxygen-evolving reaction (OER) We point out that improvements in the performance of OER catalysts will depend critically on the success of work aimed at understanding reaction barriers based on atomic-level mechanisms We highlight the challenge of obtaining acid-stable OER catalysts, with proposals for elements that could be employed to reach this goal We suggest that future advances in solar fuels science will be accelerated by the development of new methods for materials synthesis and characterization, along with in-depth investigations of redox mechanisms at catalytic surfaces

1,159 citations

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TL;DR: An overview of the characteristics of nanoparticles that could affect their behaviour and toxicity, as well as techniques available for their determination are provided, which could be optimized to provide the necessary information.
Abstract: Nanotechnology is developing rapidly and, in the future, it is expected that increasingly more products will contain some sort of nanomaterial. However, to date, little is known about the occurrence, fate and toxicity of nanoparticles. The limitations in our knowledge are partly due to the lack of methodology for the detection and characterisation of engineered nanoparticles in complex matrices, i.e. water, soil or food. This review provides an overview of the characteristics of nanoparticles that could affect their behaviour and toxicity, as well as techniques available for their determination. Important properties include size, shape, surface properties, aggregation state, solubility, structure and chemical composition. Methods have been developed for natural or engineered nanomaterials in simple matrices, which could be optimized to provide the necessary information, including microscopy, chromatography, spectroscopy, centrifugation, as well as filtration and related techniques. A combination of these is often required. A number of challenges will arise when analysing environmental and food materials, including extraction challenges, the presence of analytical artifacts caused by sample preparation, problems of distinction between natural and engineered nanoparticles and lack of reference materials. Future work should focus on addressing these challenges.

643 citations

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TL;DR: Electrochemical, kinetic, UV-vis, SEM, EDX, and other data provide four main lines of compelling evidence that, under the conditions used herein, the dominant WOC is actually heterogeneous CoO(x) and not homogeneous [Co(4)(H(2)O)(2)(PW(9)O(34))(2)](10-).
Abstract: The question of “what is the true catalyst?” when beginning with the cobalt polyoxometalate (POM) [Co4(H2O)2(PW9O34)2]10– in electrochemical water oxidation catalysis is examined in pH 8.0 sodium phosphate buffer at a glassy carbon electrode. Is [Co4(H2O)2(PW9O34)2]10– a true water oxidation catalyst (WOC), or just a precatalyst? Electrochemical, kinetic, UV–vis, SEM, EDX, and other data provide four main lines of compelling evidence that, under the conditions used herein, the dominant WOC is actually heterogeneous CoOx and not homogeneous [Co4(H2O)2(PW9O34)2]10–.

371 citations

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TL;DR: It is shown that a bimetallic Zn-Co layered double hydroxide (Zn- co-LDH) can serve as an efficient electrocatalyst and catalyst for water and alcohol oxidation, respectively.
Abstract: Replacing rare and expensive noble metal catalysts with inexpensive and earth-abundant ones for various renewable energy-related chemical processes as well as for production of high value chemicals is one of the major goals of sustainable chemistry Herein we show that a bimetallic Zn–Co layered double hydroxide (Zn–Co–LDH) can serve as an efficient electrocatalyst and catalyst for water and alcohol oxidation, respectively In the electrochemical water oxidation, the material exhibits a lower overpotential, by ∼100 mV, than monometallic Co-based solid-state materials (eg, Co(OH)2 and Co3O4)-catalytic systems that were recently reported to be effective for this reaction Moreover, the material’s turnover frequency (TOF) per Co atoms is >10 times as high as those of the latter at the same applied potentials The Zn–Co–LDH also catalyzes oxidation of alcohols to the corresponding aldehydes or ketones at relatively low temperature, with moderate to high conversion and excellent selectivity

370 citations