Linear Arrhenius Behavior Research Articles

Local Structure in Sodium Antiperovskite Ionic Conductors

Antiperovskites, which can serve as solid state electrolytes, have recently received great attention due to their high ionic conductivity[1]. Compared to typical solid-state ionic conductors, Na3OCl antiperovskite exhibits a unique ionic conductivity behavior that deviates from a linear Arrhenius behavior, in which the ionic conductivity increases rapidly with increasing temperature[2,3]. Many different structural origins affecting the ion conduction mechanism in antiperovskite have been proposed using calculation, such as vacancy/dumbbell migration[4]. The lack of direct experimental local structural investigations makes it challenging to fully understand the structural origins for high ionic conductivity, even resulting in limitations in the development of material designs for good ionic conductors. Complicating their investigation, these materials are also extremely sensitive to air, preventing many structural studies.Here, local structural investigations of Na3OCl are performed using aberration corrected scanning transmission electron microscopy (STEM) to elucidate the atomistic mechanisms underlying its high ionic conduction. To avoid degradation in air, we use an inert gas transfer system that has several advantages. First, transfer in an inert gas environment without air/moisture exposure enables the sample to retain the on-stoichiometry. Second, both room temperature and cryo experiments are possible, which allows pristine structure investigation at application relevant temperatures. Beyond the environment, Na3OCl is also very electron beam sensitive. We will show that low-dose imaging methods, such as parallel beam electron diffraction and electron ptychography, can provide new insights and allow for direct imaging of the local structure. For example, diffuse electron scattering (scattering between the Bragg reflections) is used to investigate subtle differences resulting from local structure, atomic defects, and phonon dispersion relations through combination with electron scattering simulations and Molecular Dynamics (MD) using machine learned potentials. We will then demonstrate how electron ptychography can achieve deep sub-angstrom spatial resolution with low dose conditions and provide direct insights into the migration of Na-ions. Overall, the inert gas transfer system and low-dose diffraction and STEM ptychography enable direct imaging of local structures even for reactive and electron beam sensitive materials, such as antiperovskite electrolytes. The understanding of local structure related to the high ionic conductivity will be crucial for designing high-performance solid electrolytes.

Ionic liquid incorporated metal–organic framework as high conductivity solid conductor

As a new type of composite ionic conductor, the combination of ionic liquids (ILs) and metal organic framework (MOF) shows a good application prospect. In this study, two ionic liquids, 1,3-dimethylimidazolium tetrafluoroborate ([Dmim][BF4]) and 1-Allyl-3-methylimidazolium dicyanamide ([Amim][N(CN)2]) were successfully combined with MIL-101(Cr). The influence of the amount of ionic liquid and temperature on the electrical conductivity of composite IL@MIL-101(Cr) was explored. The optimal electrical conductivity reached 3.73 × 10-3S·cm−1 ([Dmim][BF4]) and 2.69 × 10-3S·cm−1 ([Amim][N(CN)2]) respectively when exposed to air at 100 °C. It is worth noting that the ionic conductivity of all composites exhibits linear Arrhenius behavior. Since the activation energies of composites are closely related to the type of ionic liquid and MOF types, these two composites exhibit different activation energies. The reason for the difference in activation energies is analyzed with the aid of quantum chemical calculations.

Polymer-ion interactions in PVDF@ionic liquid polymer electrolytes: A combined experimental and computational study

Polymer electrolytes based on poly (vinylidene fluoride) (PVDF) with different concentrations (40, 55, 65, and 75 wt.%) of 1-methyl-3-ethylimidazolium bis(trifluoromethanesulfonyl)imide [EMIM][FSI] were investigated by experimental and molecular dynamics (MD) simulation techniques. The addition of ionic liquid (IL) slightly decreases the electrochemical stability window, as estimated by linear scanning voltammetry. For the neat PVDF, the simulated glass transition temperature (Tg) was obtained at 233.1 K, which is in good agreement with experimental data. Higher contents of IL promoted an increase of the glass transition temperature of the system, indicating a reduction of the polymer segmental mobility, possibly due to the increase of the interactions with the ions. Ionic conductivities were obtained through experimental measurements and MD simulations, which were calculated by Nernst-Einstein and Einstein-Helfand methods. The MD simulation results reproduced the general trend of the experimental ionic conductivities for the GPEs. The studied GPEs systems present an ionic conductivity that obeys a linear Arrhenius behavior, confirming that the ionic mobility is not dependent on the polymer motion.

Tuning Ionic Conductivity in Sodium Anti-Perovskite Ionic Conductors

Anti-perovskite materials have recently attracted great interest as a family of non-flammable solid state electrolytes with high ionic conduction.[1] Typical solid-state electrolyte materials have temperature dependent ionic conductivity following linear Arrhenius behavior over a substantial range of temperature, corresponding to a constant activation energy Ea. However, we have discovered several anti-perovskite materials that have strong positive deviations from Arrhenius behavior, leading to rapidly rising ionic conductivities with increasing temperature.Na3OCl and Na3OBr are typical anti-perovskite compositions with atomic structure shown in Figure 1a. Strong deviations from Arrhenius (linear) behavior were observed in the temperature dependent conductivity measured by impedance spectroscopy, where Na3OCl0.5Br0.5 reaches the highest ionic conductivity with increasing temperature, as shown in Figure 1b. The structural origins of such behavior, such as change of octahedral tilt systems and order/disorder phase transition, has been investigated using multiple temperature-resolved characterization methods including synchrotron XRD, NMR, dielectric property measurements, and calorimetry, and modeled using AIMD and DFT. This work will give insight to tuning solid state electrolyte with high ionic conductivity.This work was supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences.Figure : Temperature dependent ionic conductivity and atomic model of Na-based anti-perovskites. Figure 1

Thermoset materials characterization by thermal desorption or pyrolysis based gas chromatography-mass spectrometry methods

Thermoset materials characterization is often limited to solid state analytical techniques such as IR, NMR, DSC, TGA and mechanical testing. Alternatively, their off-gassing behavior can also be evaluated using GC based techniques such as TD-GC-MS, allowing this method to be applied to thermoset materials analyses such as identification, aging characterization, and formulation optimization. As an overview, common thermoset materials were evaluated by analyzing their gaseous degradation products via TGA-based pyrolysis and subsequent TD-GC-MS for the identification of representative volatile signatures. It is thereby possible to distinguish different classes of phenolic materials or cured epoxy resins, as well as their amine or anhydride curatives. Additionally, this method enabled quantification of a volatile fragment (bisphenol A, BPA) which is associated with oxidation of epoxy/amine thermoset materials. The amount of evolved BPA increased linearly with aging time and this trend exhibits linear Arrhenius behavior over the temperature range (80–125 °C) studied, in agreement with oxidation sensitivies based on oxygen consumption data. Further, TD-GC-MS was used to explore how off-gassing of residual anhydride curative from an epoxy/anhydride material depends on formulation stoichiometry. Even in formulations that theoretically contained enough epoxy to consume all anhydride (1:1 stoichiometry), an imperfect final cure state resulted in residual anhydride which could evolve from the material. For such materials, a slightly epoxy-rich formulation is required to ensure that the material contains no residual unreacted anhydride. Analysis of volatiles generated by thermal exposure is an attractive characterization approach enabling compositional analysis as well as complementary diagnostics for materials degradation.

Electrochemical stability of lithium halide electrolyte with antiperovskite crystal structure

The present study is focused on a relatively new class of solid-state lithium halide electrolytes with antiperovskite crystal structure that are designed to alleviate safety concerns related to conventional lithium-ion batteries. The solid-state Li3ClO electrolyte membranes were produced by a casting/delamination method and deposited on a graphite-based working electrode. The electrolyte charge transfer resistances, electrochemical performance, and chemical stability in a half-cell configuration were evaluated over a broad temperature range from room temperature up to 100 °C. The electrochemical cells with lithium metal as a reference electrode demonstrated linear Arrhenius behavior in the temperature range of 25–100 °C confirming the absence of phase transformations. Cyclic voltammetry at 50 °C and 100 °C confirms that the electrochemical cell performance during lithiation/delithiation from 0.05 to 1.00 V is reproducible within at least 100 cycles. The solid-state electrolyte electrochemical stability in contact with lithium metal is confirmed for the first time by demonstrating the constant values of charge transfer resistances during charge/discharge operations in 575 cycles at 50 °C and 1/5 C-rate. Transport of lithium ions between the lithium metal and Li3ClO electrolyte in contact with a graphite working electrode provides evidence that lithium halide antiperovskites can serve as effective and electrochemically stable electrolytes for a new generation of all-solid-state lithium-ion or lithium metal batteries.

A series of poly(butylimidazolium) ionic liquid functionalized copolymers for anion exchange membranes

A new series of ionic liquid functionalized copolymers for anion exchange membranes (AEM) is prepared. Poly(butylvinylimidazolium)(b-VIB) is copolymerized with para-methyl styrene (p-MS) by the radical polymerization formed block copolymers b-VIB/p-MS, which is crosslinked with poly(diphenylether bibenzimidazole) (DPEBI) providing the desired materials b-VIB/p-MS/DPEBI. Structures are characterized via H1NMR, FTIR spectra and elemental analysis. The b-VIB blocks offer the anion conduction function while DPEBI moieties contribute to enhancing other properties. The prepared membranes display chloride conductivity as high as 19.5 mS/cm at 25 °C and 69.2 mS/cm at 100 °C-higher than that of the commercial membrane tokuyuama A201-. Their hydroxide conductivity reaches 35.7 Scm−1 at 25 °C and 73.1 Scm−1 at 100 °C. The membranes showed a linear Arrhenius behavior in the anion conduction, low activation energies and distinguished nanophase separation of hydrophilic/hydrophobic regions by the transmission electron microscopy (TEM) studies. Thermal investigations using TGA and DSC confirm that the membranes are stable up to 250 °C. Particularly, drastically alkaline stability due to no decrease in the hydroxide conductivity after 168 h of treatment with 2M KOH.

Neon diffusion kinetics and implications for cosmogenic neon paleothermometry in feldspars

Observations of cosmogenic neon concentrations in feldspars can potentially be used to constrain the surface exposure duration or surface temperature history of geologic samples. The applicability of cosmogenic neon to either application depends on the temperature-dependent diffusivity of neon isotopes. In this work, we investigate the kinetics of neon diffusion in feldspars of different compositions and geologic origins through stepwise degassing experiments on single, proton-irradiated crystals. To understand the potential causes of complex diffusion behavior that is sometimes manifest as nonlinearity in Arrhenius plots, we compare our results to argon stepwise degassing experiments previously conducted on the same feldspars. Many of the feldspars we studied exhibit linear Arrhenius behavior for neon whereas argon degassing from the same feldspars did not. This suggests that nonlinear behavior in argon experiments is an artifact of structural changes during laboratory heating. However, other feldspars that we examined exhibit nonlinear Arrhenius behavior for neon diffusion at temperatures far below any known structural changes, which suggests that some preexisting material property is responsible for the complex behavior. In general, neon diffusion kinetics vary widely across the different feldspars studied, with estimated activation energies (Ea) ranging from 83.3 to 110.7kJ/mol and apparent pre-exponential factors (D0) spanning three orders of magnitude from 2.4×10−3 to 8.9×10−1cm2s−1. As a consequence of this variability, the ability to reconstruct temperatures or exposure durations from cosmogenic neon abundances will depend on both the specific feldspar and the surface temperature conditions at the geologic site of interest.

Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide) random copolymer functionalized with a bulky phosphonium cation

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO–TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXS revealed a cation scattering peak with a d-spacing from 7 to 15Å. Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3mS/cm at 95% RH, 90°C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel–Tamman–Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. This is particularly true for the film cast from ethyl lactate.

Diffusion kinetics of 3He and 21Ne in quartz and implications for cosmogenic noble gas paleothermometry

The simultaneous production and diffusion of cosmogenic noble gases offers the potential to constrain past temperatures on Earth and other planetary surfaces. Knowledge of both the production rate and diffusion kinetics of cosmogenic nuclide pairs is required to utilize this open-system behavior for paleothermometry. Here, we investigate the diffusion kinetics of spallogenic 3He and 21Ne in quartz through a series of step-degassing experiments on individual, proton-irradiated quartz grains. Quartz often, but not always, exhibits two stages of linear Arrhenius behavior, with He and Ne exhibiting similar release patterns. This two-stage behavior does not appear to correlate with heating-induced structural changes or anisotropy, nor is it an artifact of proton irradiation. The behavior may instead be associated with a sample-specific property such as radiation damage, mineral inclusions, fluid inclusions, or structural defects. We interpret these two Arrhenius arrays to represent multiple diffusion domain (MDD)-type behavior in quartz, as two-domain models closely reproduce the experimental data. However, we are currently unable to link this behavior with a clear physical mechanism; a different, more mechanistic model may be more appropriate in future studies.For both He and Ne, modeled Arrhenius diffusion parameters (activation energy, Ea, and pre-exponential factor, D0) display a range of values in the quartz samples analyzed. For 3He, Ea ranges from 73.0 to 99.8kJ/mol and D0 from 5.9×100 to 1.0×104cm2s−1 for the initial, low-temperature linear Arrhenius arrays; when observed, a second array at higher temperatures corresponds to Ea ranging from 85.2 to 106.4kJ/mol and D0 from 1.7×10−1 to 3.5×100cm2s−1. For 21Ne, Ea ranges from 95.7 to 153.8kJ/mol and D0 from 6.6×10−1 to 3.2×103cm2s−1 for the initial, low-temperature array; linearity at high temperatures is not well constrained, likely because the α- to β-quartz transition occurs during the relevant temperature range. When extrapolated to Earth surface temperatures and geologically relevant timescales, these results suggest that 1mm-radius quartz grains lose significant amounts of cosmogenic 3He by diffusion at sub-zero temperatures from the low-retentivity domain over >103yr timescales and from the high-retentivity domain over >104yr, whereas quantitative retention of cosmogenic 21Ne occurs over >106yr at temperatures ⩽40°C in most cases. While these results are generally consistent with previously reported studies, they also reveal that sample-specific diffusion parameters are required for quantitative application of cosmogenic noble gas paleothermometry. The cosmogenic 3He abundance in one quartz sample with a simple Holocene exposure history and the stepwise degassing pattern of cosmogenic 3He and 21Ne from another quartz sample with a ∼1.2Ma exposure history agree well with diffusion experiments on proton-irradiated aliquots of the same samples. For the sample with a simple Holocene exposure history, a production and diffusion model incorporating sample-specific diffusion parameters and the measured 3He abundance predicts an effective diffusion temperature consistent with the effective modern temperature at the sample location. This internal consistency demonstrates that the empirically determined, sample-specific diffusion kinetics apply to cosmogenic 3He and 21Ne in quartz in natural settings over geologic timescales.

Anion Transport in a Chemically Stable, Sterically Bulky α-C Modified Imidazolium Functionalized Anion Exchange Membrane

The morphology and anion transport of an α-C modified imidazolium functionalized anion exchange membrane, 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl)imidazolium functionalized polyphenylene oxide (with ion exchange capacity {IEC} = 1.53 or 1.82 mequiv/g), were studied in detail. The novel cation is less susceptible to OH– attack (0% degradation) compared to unsubstituted imidazolium functionalized polyphenylene oxide (25% degradation) after 24 h at 80 °C in 1 M KOH. The two different IEC materials (with the same protected cation) show interesting differences in membrane performance. From AFM and SAXS under humid conditions, the domain sizes of the membrane change, which impact the transport properties. The lower IEC sample showed a smaller tortuosity and, thus, needs a longer diffusion time for the water molecules to be fully hindered inside the hydrophobic clusters, which is confirmed by water self-diffusion measurements from pulsed field gradient NMR. From conductivity and diffusion measurements, the higher IEC sample exhibited Vogel–Tammann–Fulcher behavior, thus indicating that the polymer chain’s movement dominates the transport. However, the lower IEC sample exhibited the linear Arrhenius behavior signifying water-mediated transport. The maximum Cl– conductivity observed was 23 mS/cm at 95% RH and 90 °C.

Activation energy of poly(isobutylene) under thermo-oxidative conditions from 40 to 100 °C

The thermo-oxidation of poly(isobutylene) (PIB) has been investigated by using accelerated heat aging in the 40–100 °C range and functional group analysis by transmission Fourier Transform Infrared (FTIR) spectroscopy. Time–temperature superposition (TTS) and the Arrhenius approach were used to calculate activation energies. Oxidation product evolution was continuous within the temperature range. PIB displayed excellent TTS and linear Arrhenius behavior leading to an energy of activation (Ea) range of 116–125 kJ/mol for the growths of the carbonyl (ketone), hydroxyl and β-lactone groups. The similarity between the Ea values strongly suggests that the reactions that they comprise are interrelated, agreeing with the currently accepted oxidation mechanisms of PIB.

Determination of flow activation energy at viscosity maximum for spherical and wormlike micelles of different lengths and flexibility

Steady shear rheological measurements were carried out on aqueous solutions containing 15 mM cetyltrimethylammonium bromide (CTABr) and a constant value of [MX] and temperature for MX = 2,3-; 2,4-; 2,5-; 2,6-; 3,4-; and 3,5-Cl2BzNa with Bz−representing C6H3CO2. Plots of zero shear viscosity (η 0) vs. [MX] at 35 °C and 15 mM CTABr show the presence of single maximum and double maxima for MX = 2,3- and 3,5-Cl2BzNa, respectively. Turbidity data (absorbance at 600 nm vs. [MX]) coupled with η 0vs. [MX] data at 35 °C reveal indirectly the presence of vesicles along with wormlike micelles (WM) at MX / CTABr > 0. 7 for MX = 3,5-Cl2BzNa. Temperature dependence of η 0in the vicinity of the viscosity maximum shows nonlinear and linear Arrhenius behavior, within the temperature range of 20–55 °C, for MX = 2,3-; 2,4-; 2,5-; 3,4-; and 3,5-Cl2BzNa, respectively. The values of η 0, $\dot {\gamma }_{\text {cr}} $ (critical shear rate), and flow activation energy correlate with CTABr micellar binding constants of counterions.

Sequence and Temperature Dependence of the End-to-End Collision Dynamics of Single-Stranded DNA

Intramolecular collision dynamics play an essential role in biomolecular folding and function and, increasingly, in the performance of biomimetic technologies. To date, however, the quantitative studies of dynamics of single-stranded nucleic acids have been limited. Thus motivated, here we investigate the sequence composition, chain-length, viscosity, and temperature dependencies of the end-to-end collision dynamics of single-stranded DNAs. We find that both the absolute collision rate and the temperature dependencies of these dynamics are base-composition dependent, suggesting that base stacking interactions are a significant contributor. For example, whereas the end-to-end collision dynamics of poly-thymine exhibit simple, linear Arrhenius behavior, the behavior of longer poly-adenine constructs is more complicated. Specifically, 20- and 25-adenine constructs exhibit biphasic temperature dependencies, with their temperature dependences becoming effectively indistinguishable from that of poly-thymine above 335 K for 20-adenines and 328 K for 25-adenines. The differing Arrhenius behaviors of poly-thymine and poly-adenine and the chain-length dependence of the temperature at which poly-adenine crosses over to behave like poly-thymine can be explained by a barrier friction mechanism in which, at low temperatures, the energy barrier for the local rearrangement of poly-adenine becomes the dominant contributor to its end-to-end collision dynamics.

Extreme-ultraviolet secondary electron blur at the 22-nm half pitch node

In this paper the Arrhenius behavior of blur upon extreme ultraviolet (EUV) exposure is investigated through variation of the post-exposure bake (PEB) temperature. In this way, thermally activated parameters that contribute to blur (such as acid/base diffusion) can be separated from nonthermally activated parameters (such as secondary electron blur). The experimental results are analyzed in detail using multiwavelength resist modeling based on the continuum approach and through fitting of the EUV data using stochastic resist models. The extracted blur kinetics display perfectly linear Arrhenius behavior, indicating that there is no sign for secondary electron blur at 22-nm half pitch. At the lowest PEB setting the total blur length is ∼4 nm, indicating that secondary electron blur should be well below that. The stochastic resist model gives a best fit to the current data set with parameters that result in a maximum probability of acid generation at 2.4 nm from the photon absorption site. Extrapolation of the model predicts that towards the 16-nm half pitch the impact on sizing dose is minimal and an acceptable exposure latitude is achievable. In order to limit the impact on linewidth roughness at these dimensions it will be required to control acid diffusion to ∼5 nm.

Degradation and accelerated ageing of poly(ether block amide) thermoplastic elastomers

AbstractUnstabilized poly(ether block amide) (PEBA, PEBAX) of the type used in angioplasty balloons was aged at temperatures of 18–85°C for periods of up to 313 days. Since PEBA is used in safety critical applications, understanding the effects and underlying mechanisms of ageing and the validity of accelerated ageing protocols is vital. Mechanical testing indicated an increase in modulus during ageing consistent with embrittlement. An activation energy (Ea) of 47.3 kJ mol−1 was calculated over the temperature range 18–45°C and increased deviation from linear Arrhenius behavior observed above 45°C. This value of Ea would result in the commonly applied 10°C rule over estimating shelf life. Fourier Transform Infrared Spectroscopy, Gel Permeation Chromatography, and thermal analysis provided evidence that the observed property changes were largely the result of oxidative damage and crystallinity effects. The data presented provides a rational basis for the use of accelerated testing protocols at temperatures of up to 45°C to generate room temperature shelf life estimates. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Lower critical solution temperature determination of smart, thermosensitive N‐isopropylacrylamide‐alt‐2‐hydroxyethyl methacrylate copolymers: Kinetics and physical properties

AbstractThe lower critical solution temperatures (LCSTs) were verified and determined for different molar feed ratios of N‐isopropylacrylamide (NIPAAm) and 2‐hydroxyethyl methacrylate (HEMA) monomers with ultraviolet spectroscopy and differential scanning calorimetry techniques. Increases in the NIPAAm monomer content played a crucial role in the LCST, which increased up to 36.7°C at 50 mol %. However, a further increase in the NIPAAm monomer content steadily reduced the LCST, which decreased to 33°C at 100 mol % NIPAAm [i.e., pure poly(N‐isopropylacrylamide)]. The rate of copolymerization, assessed by the conventional conversion (%)–time method, and the apparent activation energies were determined. The reactivity ratios of the monomers, determined by the Kelen–Tudos and Fineman–Ross techniques, together with the results of an equation, showed that the copolymer which formed was an alternating copolymer. The Q–e values for the NIPAAm monomer were determined. The equation showed the linear Arrhenius behavior of ln(r1r2) versus the reciprocal of the temperature (where r1 and r2 are the reactivity ratios of NIPAAm and HEMA, respectively): the activation energy difference [i.e., (E12 + E21) − (E11 + E22), where E12, E21, E11, and E22 are various activation energies] was found to be −109 kJ/mol. The copolymers were characterized with 1H‐NMR, 13C‐NMR, Fourier transform infrared, ultraviolet–visible, thermogravimetric analysis, differential scanning calorimetry, X‐ray diffraction, and scanning electron microscopy techniques. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Mechanism of [formula omitted] and CO formation in the catalytic partial oxidation of [formula omitted] on Rh probed by steady-state spatial profiles and spatially resolved transients

Spatially resolved species and temperature profiles have been measured for the catalytic partial oxidation of CH 4 on autothermally operated Rh-coated α - Al 2 O 3 foams in both steady state and transient mode. A probe consisting of a thin quartz capillary and a thermocouple was moved with sub-mm resolution through the catalyst/heat shield stack to sample the gases into a mass spectrometer and measure temperature. The probe was also used to follow the relaxation of the system upon perturbation by stepping the stoichiometry of the reactants periodically. The spatial profiles in steady state show that H 2 and CO are formed in presence of gas phase oxygen (oxidation zone) and after total oxygen conversion by steam reforming (reforming zone). The stepwise change of the reactant stoichiometry in the transient experiments allowed decoupling chemistry (ms timescale) and temperature (s timescale). By exposing a catalyst, initially operating very hot at C / O = 0.6 , suddenly to a CH 4 rich feed ( C / O = 1.4 ) , it was possible to follow how the integral H 2 and CO production rates decrease with decreasing temperature of the catalyst. The reverse switch from C / O = 1.4 to 0.6 showed how the integral H 2 and CO production rates increased with increasing temperature of the catalyst. Differential reaction rates were obtained by performing these transients spatially resolved at two adjacent points in the catalyst. For C / O = 0.6 → 1.4 , H 2 and CO formation show a strict linear Arrhenius behavior over the entire temperature range from ∼ 1100 to ∼ 600 ∘ C . For C / O = 1.4 → 0.6 , the Arrhenius plots show two straight segments, a steep increase in the formation rate from ∼ 630 to ∼ 710 ∘ C and a weak increase from ∼ 725 to ∼ 1000 ∘ C . In both cases, H 2 formation is more activated than CO formation indicating two different rate determining steps.

Pore-filling solvent-free polymer electrolytes based on porous P(VdF-HFP)/P(EO-EC) membranes for rechargeable lithium batteries

Highly porous membranes consisting of poly(vinylidene fluoride- co-hexafluoropropylene) [P(VdF-HFP)] and poly(ethylene oxide- co-ethylene carbonate) [P(EO-EC)] were prepared by a phase inversion method using acetone as a solvent and ethylene glycol as a nonsolvent. The presence of viscous P(EO-EC) in the membranes not only contributes to their flexibility but also results in increases in their pore size and porosity. Pore-filling solvent-free polymer electrolytes (SPEs) were then prepared by filling the pores of the porous membranes with viscous P(EO-EC) complexed with LiCF 3SO 3. The ionic conductivities of the SPEs were found to exhibit Arrhenius temperature dependences, with the highest value of 3.7 × 10 −5 S cm −1 at 298 K for E-V6E4; ‘E-V xE y’ denotes an electrolyte with a P(VdF-HFP)/P(EO-EC) matrix ( x/ y by wt%) filled with P(EO-EC)/LiCF 3SO 3 (in the case of E-V6E4, ca. 61 wt%). The temperature dependences of ln τ c ( τ c is the correlation time) obtained from 7Li NMR linewidth measurements were found for all the SPEs to consist of two distinct regions, above and below the temperature of slope change, T sc, with linear Arrhenius behavior in each region. Above T sc, the temperature region in which the conductivity measurements were carried out, the correlation times, τ c, and the corresponding activation energies, E a, were found to decrease with increases in the amount of P(EO-EC)/LiCF 3SO 3 electrolyte.

Amelioration of mechanical brittleness in hyperbranched polymer. 1. Macroscopic evaluation by dynamic viscoelastic relaxation

Hyperbranched poly(ether ketone)- b-linear poly(ether ketone)- b-hyperbranched poly(ether ketone) (HLHPEK) triblock copolymers with two different block compositions were prepared as an approach to improve the mechanical brittleness of hyperbranched poly(ether ketone) (HPEK). From the time–temperature superposition of dynamic shear moduli, G′( ω) and G″( ω), of HPEK and two HLHPEKs, it was investigated that the junction points between G′( ω) and G″( ω) shifted to the higher frequencies and the rubbery plateau region spread wider over the reduced frequency axis as the linear blocks were introduced and their compositions were increased. Such changes in viscoelastic response were consequences of increase in the amount of chain entanglements additionally formed by the linear blocks. In order to verify the effect of the linear block incorporation on amelioration of the mechanical brittleness, the degree of brittleness and its improvement were evaluated from the temperature dependence of the shift factors, a T s, experimentally obtained during the superposition of the dynamic moduli and of the average viscoelastic relaxation times, τ HNs, determined with empirical Havriliak–Negami distribution function. From the nonlinear curve fittings of the a T s and the τ HNs by the Vogel–Tamman–Fulcher equation, the degree of brittleness for HPEK and HLHPEK triblock copolymers were quantified as values of the material parameter D, an indicative of deviation from the linear Arrhenius behavior and a measure of fragility of the given material. The tendency of increasing D values with the linear block compositions confirmed substantial improvement of the mechanical brittleness in the HLHPEK triblock copolymers compared to HPEK. Therefore, the approach to copolymerize HPEK with its chemically analogous linear counterpart was verified to be an effective strategy to impart molecular entanglements and hence ameliorate the mechanical brittleness on the basis of macroscopic rheological evaluation.