Effect of molecular weight on conductivity of polymer electrolytes

The ionic conductivity, σ, of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfone)imide (LiTFSI) was measured as a function of molecular weight of the PEO chains, M, over the range 0.2-5000 kg/mol. Our data are consistent with an expression σ = σ₀ + K/M proposed by Shi and Vincent [Solid State Ionics 60 (1993)] where σ₀ and K are exponential and linear functions of inverse temperature respectively. Explicit expressions for σ₀ and K are provided.     

Biomass-derived oxygenate reforming on Pt(111): A demonstration of surface science using d-glucose and its model surrogate glycolaldehyde

Molecules derived from cellulosic biomass, such as glucose, represent an important renewable feedstock for the production of hydrogen and hydrocarbon-based fuels and chemicals. Development of efficient catalysts for their reformation into useful products is needed; however, this requires a detailed understanding of their adsorption and reaction on catalytically active transition metal surfaces. In this paper we demonstrate that the standard surface science techniques routinely used to characterize the reaction of small molecules on metals are also amenable for use in studying the adsorption and reaction of complex biomass-derivatives on single crystal metal surfaces. In particular, Temperature Programmed Desorption (TPD) and High Resolution Electron Energy Loss Spectroscopy (HREELS) combined with Density Functional Theory (DFT) calculations were used to elucidate the adsorption configuration of d-glucose and glycolaldehye on Pt(111). Both molecules were found to adsorb in an η₁ aldehyde configuration partially validating the use of simple, functionally-equivalent model compounds for surface studies of cellulosic oxygenates.     

Kinetics of Nitroxide Mediated Radical Polymerization of Styrene with Unimolecular Initiators

Summary: This study examined the kinetics of nitroxide-mediated radical polymerization of styrene with unimolecular (alkoxyamine) initiators. Control of polymerization rate and polymer molecular weight in unimolecular nitroxide-mediated radical polymerization was studied by looking at the effects of the three main factors: initiator concentration, temperature, and initiator molecular weight on polymerization rate, molecular weight and polydispersity. In addition, the behavior of the unimolecular initiating systems was compared to that of the corresponding bimolecular system. The effective TEMPO concentration and degree of self-initiation of styrene were proved to be significant in dictating magnitudes of molecular weight averages and widths of molecular weight distribution.     

Pulsed quantum cascade laser instrument with compact design for rapid, high sensitivity measurements of trace gases in air

We have developed a compact instrument for sensitive, rapid and continuous measurement of trace gases in air, with results presented here for methane (CH₄), nitric oxide (NO), nitrous oxide (N₂O) and ammonia (NH₃). This instrument takes advantage of recent technology in quantum cascade (QC) lasers and infrared detectors, which allows high sensitivity without cryogenic liquids, e.g., 0.2 ppb (0.2×10^-9) of NH₃ in air in 1 s. One may substitute a QC laser operating at a different wavelength to measure other gases. The instrument operates continuously, requiring little operator attention, and web-based remote access is provided for instrument control, calibration and data retrieval. The instrument design includes a thermoelectrically (TE) cooled pulsed distributed feedback (DFB) QC laser, a low volume (0.5 l) multipass cell offering 76 m absorption path length and a TE cooled detector. Integrated software for laser control and data analysis using direct absorption provides quantitative trace gas measurements without calibration gases. The instrument may be applied to field measurements of gases of environmental concern. PACS  07.57.Ty; 42.62.Fi; 92.70.Cp     

Conformational analysis of tertiary cycloalkyl (C6,C7,C8) carbocations using molecular mechanics. Comparison with stable ion experimental data

Conformational calculations of the 1-methylcyclohexyl, 1-methylcycloheptyl, and 1-methylcyclooctyl cations agree with reported experimental observations.     

The hydrogenation of α-methylstyrene by tricarbonyl(cyclopentadienyl)hydride compounds of tungsten and molybdenum; support for a radical mechanism

Rates of reaction of the hydrides of tungsten and molybdenum of the form HM(η5-C₅H₅(CO)₃, with β-methylstyrene have been determined. The rate law is first order in olefin and in hydride. A mechanism involving a rate limiting step of hydrogen atom transfer to the olefin is consistent with the rate law, isotope effect and the absence of CO inhibition. The activation enthalpy for the reactions of HW(η5-C₅H₅)(CO)₃ and HMo(η5-C₅H₅)(CO)₃ are 97.5 ± 4.2 and 89.1 ± 3.3 kJ/mol, respectively. The rate constant for the reaction of styrene and HW(β5-C₅H₅)(CO)₃ is approximately that of β-methylstyrene, while β-methylstyrene was not observed to react under the conditions of the previous determinations. This suggests that attack by the hydride occurs at the β-carbon and this process is inhibited by substituents at that location.