Ionic conduction in composite polymer electrolytes at subambient temperatures

The majority of investigations carried out on polymer(SINGLEBOND) salt systems have been on polyether electrolytes at moderate temperatures where such electrolytes exhibit macroscopic uniformity. Relatively little attention has been paid to the subambient temperature region where composite electrolytes based on polyethers exhibit much higher conductivities than their pure polyether electrolyte analogues. For all of the composite systems studied the conduction mechanism changes from one in which the ions are coupled to the polymer segmental relaxations to one in which the ions are decoupled and thermally activated ionic hopping produces higher conductivities than would be expected from ion-segmental coupling and higher than observed for the base polyether(SINGLEBOND) salt system. This change has been observed at temperatures between 10 and 80°C above the respective glass transition temperatures. The relationship between this interaction and these higher conductivities at subambient temperatures is explored and discussed. © 1996 John Wiley & Sons, Inc.     

Analysis of degradation products by thermal volatilization analysis at subambient temperatures

In the subambient thermal volatilization analysis (TVA) technique, degradation products initially at ?196°C are allowed to warm up to ambient temperature in a controlled manner under vacuum conditions, and volatilization from the sample tube to a trap at ?196°C is monitored by means of a Pirani gauge. The technique is discussed in relation to earlier TVA work in which volatilization from a heated polymer sample was followed. Design and operation of a subambient TVA system are described, and examples of the application of the technique to the study of the degradation products of seven polymers are considered.     

Thermophysical Properties of CeB6 and PrB6 at subambient temperatures

Equilibrium adiabatic heat-capacity measurements have been made on zone refined samples of CeB₆ and PrB₆. Companion measurements made on LaB₆, NdB₆, and GdB₆ have been reported elsewhere. These show cooperative lambda-type anomalies associated with antiferro-magnetic ordering. Except for lanthanum hexaboride, Schottky internal crystal field levels result in significant contributions to the thermodynamic functions. The gross thermodynamic properties at 298.15 K heat capacity (C_p/R), entropy increment (Δ^T _0,m S ⁰/R), and Gibbs energy function are correlated with the nature of the lanthanide. For LaB₆, CeB₆, PrB₆, NdB₆, and GdB₆ the three properties are, respectively: {11.654, 12.014, 11.997, 11.916, 11.695} Cp/R; {10.001, 11.803, 12.430, 12.558, 13.982} S⁰/R, and finally {4.379, 5.912, 6.232, 6.451, 7.905}Φ⁰ _m/R. This revised version was published online in August 2006 with corrections to the Cover Date.     

Isocratic separation of ginsenosides by high-performance liquid chromatography on a diol column at subambient temperatures

An improved high-performance liquid chromatographic method for separation of a number of ginsenosides has been developed. The influence of temperature (from 0 to 25°C) on the retention and separation of the ginsenosides was studied by applying a binary mobile phase (acetonitrile/water, 82:18 v/v) and a diol column (LiChrospher 100 Diol). The column temperature is one of the more important parameters for the retention and separation of the components investigated. Selected thermodynamic parameters, including changes of enthalpy (ΔH°) and entropy (ΔS°), were estimated from linear van’t Hoff plots, and possible retention mechanisms were discussed. Moreover, the best separation conditions were selected based on optimization criteria including maximum retention time (t _{R max}), minimum resolution (R _{s min}), and relative resolution product (r). Temperature regions close to 14°C offered the highest selectivity and almost equal distribution of the ginsenosides peaks across the chromatogram. Under such isocratic conditions, excellent separation of chromatographic standards and selected ginseng samples was achieved in less than 16 min.     

Micromachining of Parylene C for bioMEMS

Recent advances in the micromachining of poly(p‐xylylenes), commercially known as Parylenes, have enabled the development of novel structures and devices for microelectromechanical systems (MEMS). In particular, Parylene C (poly[chloro‐p‐xylylene]) has been explored extensively for biomedical applications of MEMS given its compatibility with micromachining processes, proven biocompatibility, and many advantageous properties including its chemical inertness, optical transparency, flexibility, and mechanical strength. Here we present a review of often used and recently developed micromachining process for Parylene C, as well as a high‐level overview of state‐of‐the‐art Parylene hybrid and free film devices for biomedical MEMS (bioMEMS) applications, including a discussion on its challenges and potential as a MEMS material. Copyright © 2015 John Wiley & Sons, Ltd.     

Parylene C coating for high-performance replica molding

This paper presents an improvement to the soft lithography fabrication process that uses chemical vapor deposition of poly(chloro-p-xylylene) (parylene C) to protect microfabricated masters and to improve the release of polymer devices following replica molding. Chemical vapor deposition creates nanometre thick conformal coatings of parylene C on silicon wafers having arrays of 30 μm high SU8 pillars with densities ranging from 278 to 10,040 features per mm(2) and aspect ratios (height : width) from 1 : 1 to 6 : 1. A single coating of parylene C was sufficient to permanently promote poly(dimethyl)siloxane (PDMS) mold release and to protect masters for an indefinite number of molding cycles. We also show that the improved release properties of parylene treated masters allow for fabrication with hard polymers, such as poly(urethane), that would otherwise not be compatible with SU8 on silicon masters. Parylene C provides a robust and high performance mold release coating for soft lithography microfabrication that extends the life of microfabricated masters and improves the achievable density and aspect ratio of replicated features.     

Variable temperature solution and cp-mas C NMR of [Mo(CO)3(diglyme)]. Displacement of diglyme by solvents at subambient temperatures

Variable temperature solution ¹³C NMR of [Mo(CO)₃(diglyme)] shows that the chelating diglyme ligand is displaced by the monodentate solvents acetone, methanol and ethanol at low temperature. Free and coordinated solvent are observed at low temperature while at ambient temperature rapid exchange prevents the observation of coordinated solvent.     

Engineering considerations for growth of bacteria at temperatures around 100°C

Laboratory results from studies of three extremely thermophilic sulfur-dependent archaebacteria (Pyrodictium occultum, Pyrodictium brockii, andPyrococcus furiosus) are used to illustrate both metabolic characteristics and engineering challenges associated with bacteria growing around 100°C. Low biomass yields, production of large amounts of hydrogen sulfide, and, in one instance, metabolic formation of a growth-inhibiting product are among the many characteristics that complicate the development of bioreactors and protocols for culturing these microorganisms. Engineering considerations related to the metabolic features of the sulfur-dependent archaebacteria are also discussed     

The phase diagram of fullerene C60 at high temperatures and pressures

Experimental and literature data were used to calculate the Gibbs energies of polymerized C₆₀ phases and construct the equilibrium T-p phase diagram of fullerene C₆₀ at temperatures from 0 to 1000 K and pressures from 0 to 8 GPa. The diagram contains stability regions of the orthorhombic, tetragonal, and rhombohedral polymerized C₆₀ phases and primitive cubic (PC) and face-centered cubic (FCC) nonpolymerized C₆₀ phases. The orthorhombic phase (linear polymer) is an equilibrium phase at 298 K and 1 bar and in the adjacent region. The equilibrium line observed experimentally (FCC C₆₀—orthorhombic phase) is well described by the phase diagram. The optimum temperatures and pressures of the synthesis of polymerized phases are determined by kinetic rather than thermodynamic parameters.     

Soot formation from C2H2 and C2H4 pyrolysis at different temperatures

A study of the pyrolysis of two hydrocarbons, C₂H₂ and C₂H₄, at different temperatures has been carried out in order to compare their behaviour in terms of soot and gas yields and gas composition. Pyrolysis experiments have been performed in the same conditions for both hydrocarbons: an inlet hydrocarbon concentration of 15,000 ppmv and a temperature range of 1000–1200 °C. For C₂H₂ and C₂H₄ pyrolysis tests, the results present the same trend when increasing the temperature: an increase in soot yield, a decrease in gas yield and a similar evolution of the outlet gases. Comparatively, it can be observed that acetylene is a more sooting hydrocarbon than ethylene for a given temperature. Additionally, the study of soot reactivity with O₂ and NO shows that the soot samples obtained from ethylene show a slightly higher reactivity towards O₂ and NO than the soot samples formed from acetylene.     

Topochemical 3D polymerization of C60 under high pressure at elevated temperatures

Fullerene C60 monomer crystals were compressed to a face-centered cubic (fcc) phase with a lattice parameter of a = 11.93(5) A and a micro-Vickers hardness of 4500 kg/mm2 using high-pressure and high-temperature conditions of 15 GPa at 500-600 degrees C. The hardness is compatible with that of cubic boron nitride (c-BN), suggesting the formation of a 3D C60 polymer. The single-crystal X-ray structural analysis revealed that each C60 molecule in the polymer was linked to the 12 nearest neighbors by [2+2] cycloaddition between the common pentagon-hexagon (56) edges. However, ab initio geometry optimization and molecular dynamics calculations suggested that the 3D polymer should have a rhombohedral structure with the space group of R containing [3+3] cycloaddition between the pentagons of C60 molecules within the plane perpendicular to the 3-fold axis. The higher apparent symmetry of fcc was observed as an averaged structure of different orientations of the rhombohedral structure. The R structure can be derived by only a slight rotation of each C60 unit in the (111) plane of the fcc structure. The band-structure calculation suggested that the 3D polymer (R) was a semiconductor; the activation energy for the electrical conductivity was experimentally determined to be 0.25 eV at 550 K.     

The ammonia-ammonium equilibrium in seawater at temperatures between 5 and 25°C

The stability constantK ₁of the equilibrium NH ₃ +H⁺NH ₄ ⁺ was determined by potentiometric titration in synthetic seawaters of 5 to 40 (per mille) salinity and sodium chloride solutions between 0.2 and 0.7M ionic strength at temperatures of 5, 15 and 25°C. Moreover,K ₁was determined in sulfate-free seawater of 35 salinity and 25°C. The dependence of logK ₁on salinity (or ionic strength) and temperature can be reasonably well described by linear relations. TheK ₁obtained for sulfate-free seawater agrees very well with earlier experimental results and theoretical predictions. From the measuredK ₁and literature data on the equilibrium NH ₃ (atm)NH ₃ (aq., NaCl), the atmospheric concentration of ammonia at equilibrium with seawater was estimated.     

Stabilization at high temperatures

A general detailed model of polymer oxidative degradation in the presence of a stabilizer-oxygen acceptor was considered. The motion of the degradation zone boundary and the sample lifetime were obtained for various conditions of the process. In particular, it is shown that within the given concentration immobile oxygen acceptor has the best stabilizing properties. The theoretical results are compared with the experimental data obtained by using two independent methods: polymer sample cracking and a change in the ESR signal. Good agreement between theory and experiment was obtained.     

Conductance of salts at moderate and high concentrations in propylene carbonate-dimethoxyethane mixtures at temperatures from −45°C to 25°C

The specific conductances of LiClO₄, KSCN, KPF₆, and Et₄NPF₆ in propylene carbonate-dimethoxyethane mixtures are reported for moderate to high concentrations at temperatures between –45°C to 25°C. The data analysis was established on the base of an empirical conductance equation permitting equally well adapted fits for all electrolyte solutions irrespective of temperature, electrolyte compound and solvent composition. The effects on the conductance resulting from ion-ion, ion-solvent interactions and solvent viscosity are rationalized in terms of the thermodynamic and hydrodynamic parameters characterizing the behaviour of electrolytes in dilute solutions. Some basic aspects are discussed for optimizing the conductance of battery electrolytes, especially those of high energy density batteries.     

X-Ray diffraction at high temperatures

Experimental equipment for X-ray diffraction at high temperatures is introduced and the possibility to directly observe the evolution of the atomic (geometric) structure as a function of temperature is discussed. Recent results on crystallization investigations of amorphous iron-based alloys and on the structural development in thin molybdenum sulphide films are given. The kinetics of the process was followed by means of time resolved experiments in both cases.     

Thermometric titrations at elevated temperatures

The oxidizing power of hexacyanoferrate(III) in alkaline conditions is wellknown. Unfortunately many if its oxidation reactions are too slow at room temperatures for direct titrimetric procedures. A method has been developed for the determination of millimolar amounts of selenium(IV), arsenic(III), antimony(III), chromium(III), and thallium(I) using thermometric titrimetry at approximately 330 K. The reproducibility and accuracy of the method are approximately 1%.