Conductivity Measurements of a Con jugated-Polymer Single crystal at Lower Temperature

The conductivities in bis-(p-toluene sulfonate) or 2,4-hexa-diyne-1,6-diol(TS) and its polymer PTS single crystal were measured by means of a special device at a range of temperature from 77K to 373K (353K for TS) . Anomalies of the conductivity of TS and PTS along c-axes which are the directions of PTS at the temperature corresponding to their low temperature phase transition were observed. The temperature of phase transition in TS obtained from anomalies' of conductivity are 163K and 208K.     

在确定的热力学状态下测量气体导热系数与黏度

气体的导热系数和黏度是重要的热物性参数,其数值大小取决于所处的热力学状态。在目前的导热系数和黏度主要测量方法中,待测工质在测量时需经历非定常的过程或处于具有物性梯度的非平衡态之下,使得待测工质的物性在时间或者空间上不处于一个确定的热力学状态。本文利用圆柱定程干涉法,通过分析气体导热系数和黏度导致的声波能量耗散,结合气体输运理论中对稀疏气体的描述,探索了在确定的热力学状态下同时测量气体导热系数和黏度的方法,并以氩(Ar)为例进行了实验验证。测量结果与已有文献一致性较好,初步证实了方法的可行性。     

Crystallization of Polymers Studied by Temperature Modulated Calorimetric Measurements at Different Frequencies

Quasi-isothermal temperature modulated DSC (TMDSC) were performed during crystallization to determine heat capacity as function of time and frequency. Non-reversible and reversible phenomena in the crystallization region of polymers were distinguished. TMDSC yields new information about the dynamics of local processes at the surface of polymer crystals, like reversible melting. The fraction of material involved in reversible melting, which is established during main crystallization, keeps constant during secondary crystallization for polycaprolactone (PCL). This shows that also after long crystallization times the surfaces of the individual crystallites are in equilibrium with the surrounding melt. Simply speaking, polymer crystals are living crystals. A strong frequency dependence of complex heat capacity can be observed during and after crystallization of polymers.This revised version was published online in November 2005 with corrections to the Cover Date.     

Determination of Temperature Gradients with Micrometric Resolution by Local Open Circuit Potential Measurements at a Scanning Microelectrode

A method to determine localized temperature profiles using a scanning electrochemical microscopy (SECM) setup and potentiometry is presented. A Pt microelectrode was first calibrated to correlate the open circuit potential (OCP) with temperature in an electrolyte containing ferri/ferrocyanide. Using the calibration graph, the temperature at a given position and a time could be derived. For dynamic measurements, the thermal expansion of the surface was initially determined using shear force mode SECM. Following the OCP at the microelectrode static as well as dynamic temperature gradients above the heated surface were successfully probed and visualized with vertical micrometric resolution and with precision in temperature determination below 1 °C.     

Density and Rotational Temperature Measurements of the OH° and NO° Radicals Produced by a Gliding Arc in Humid Air

The predominant reactive species of a gliding arc in humid air, 50% relative humidity (50% RH), are identified from emission spectroscopy measurements to understand and explain the glidarc plasma interaction with aqueous solutions. The rotational temperatures of the main particles (i.e., the OH° and NO° radicals) are derived from comparing experimental and synthetic spectra at various locations in the plasma stream with different airflow rates. The temperatures decrease rather moderately downstream from the starting section of the arc (the neck) and they rather steeply increase with increasing the mass flow rate. Density measurements are also performed for the same experimental conditions to determine their evolution in the non-equilibrium zone. Although they are quasi-constant along the plasma jet axis, the OH° density is much higher than the NO° one. The chemical processes, which may lead to a constant regeneration of these prevailing reactive particles in a humid air gliding arc plasma, are also discussed. The complex composition of the plasma gas makes other chemical processes fairly possible, which may result in abundant species depending on the compound proportions.     

激光诱导等离子体中的电子密度和电子温度的测量

脉冲激光诱发等离子体的谱诊断技术用来对其电子密度和电子温度的测量结果与理论计算进行了比较，同时讨论了运用这个方法的物理条件．     

Solubility Measurements of Crystalline NiO in Aqueous Solution as a Function of Temperature and pH

Results of solubility experiments involving crystalline nickel oxide (bunsenite) in aqueous solutions are reported as functions of temperature (0 to 350 °C) and pH at pressures slightly exceeding (with one exception) saturation vapor pressure. These experiments were carried out in either flow-through reactors or a hydrogen-electrode concentration cell for mildly acidic to near neutral pH solutions. The results were treated successfully with a thermodynamic model incorporating only the unhydrolyzed aqueous nickel species (viz., Ni²⁺) and the neutrally charged hydrolyzed species (viz., Ni(OH)₂⁰)\mathrm{Ni(OH)}_{2}^{0}). The thermodynamic quantities obtained at 25 °C and infinite dilution are, with 2σ uncertainties: log₁₀K_s0^o = (12.40 ±0.29),\varDelta_rG_m^o = -(70. 8 ±1.7)\log_{10}K_{\mathrm{s0}}^{\mathrm{o}} = (12.40 \pm 0.29),\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = -(70. 8 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rH_m^o = -(105.6 ±1.3)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = -(105.6 \pm 1.3) kJ⋅mol⁻¹; \varDelta_rS_m^o = -(116.6 ±3.2)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} =-(116.6 \pm 3.2) J⋅K⁻¹⋅mol⁻¹; \varDelta_rC_p,m^o = (0 ±13)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = (0 \pm 13) J⋅K⁻¹⋅mol⁻¹; and log₁₀K_s2^o = -(8.76 ±0.15)\log_{10}K_{\mathrm{s2}}^{\mathrm{o}} = -(8.76 \pm 0.15); \varDelta_rG_m^o = (50.0 ±1.7)\varDelta_{\mathrm{r}}G_{m}^{\mathrm{o}} = (50.0 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rH_m^o = (17.7 ±1.7)\varDelta_{\mathrm{r}}H_{m}^{\mathrm{o}} = (17.7 \pm 1.7) kJ⋅mol⁻¹; \varDelta_rS_m^o = -(108±7)\varDelta_{\mathrm{r}}S_{m}^{\mathrm{o}} = -(108\pm 7) J⋅K⁻¹⋅mol⁻¹; \varDelta_rC_p,m^o = -(108 ±3)\varDelta_{\mathrm{r}}C_{p,m}^{\mathrm{o}} = -(108 \pm 3) J⋅K⁻¹⋅mol⁻¹. These results are internally consistent, but the latter set differs from those gleaned from previous studies recorded in the literature. The corresponding thermodynamic quantities for the formation of Ni²⁺ and Ni(OH)₂⁰\mathrm{Ni(OH)}_{2}^{0} are also estimated. Moreover, the Ni(OH)₃ ^-\mathrm{Ni(OH)}_{3}^{ -} anion was never observed, even in relatively strong basic solutions (m_{OH ^-} = 0.1m_{\mathrm{OH}^{ -}} = 0.1 mol⋅kg⁻¹), contrary to the conclusions drawn from all but one previous study.     

Unsaturation Characterization of Polyolefins by NMR and Thermal Gradient NMR (TGNMR) with a High Temperature Cryoprobe

Summary: It is important to identify the types of unsaturation and to quantify the amount of unsaturation in polyolefins for understanding chain termination mechanisms of polymerization with different catalysts. Unsaturation is also closely related to processibility, weatherability of polyolefin products and the level of antioxidants to be added for stabilizing purposes. However, it can be very challenging to accurately measure samples with a low level of the unsaturation within a reasonable amount of NMR acquisition time, along with some challenging technical issues, such as dynamic range with ¹H NMR. This paper reports a new method to accurately quantify unsaturation by using multi peak presaturation ¹H NMR with a high temperature NMR cryoprobe. The limit of quantification can be less than 1 unsaturation/1,000,000 carbons with about 30 min NMR acquisition. This paper also introduces a new technique, temperature gradient NMR (TGNMR) with or without substrates, to characterize unsaturation distribution directly in NMR tube upon temperature change.     

Temperature Control Modes in Thermal Analysis

Now we can use several temperature control modes, i.e., the isothermal run including stepwise heating and cooling, constant rate heating (or cooling), temperature control for sample thermal history, sample controlled thermal analysis (SCTA or controlled-rate thermal analysis, CRTA), temperature jump, rate jump, temperature modulation and repeated temperature scanning. Their advantages and drawbacks are reviewed with some illustrative examples, especially for application to kinetic analysis. The combined use of these varieties of temperature control mode is recommended by showing examples. Temperature modulation and repeated temperature scanning are discussed in comparison with temperature modulated DSC, and common and analogous points are elucidated. In relation to this, the possibility that an imaginary part of overall reaction rate constant in complex reaction is postulated. Finally,these modes are classified and tabulated from two viewpoints and other possible modes are shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Temperature Frequency Response Method for Adsorption Kinetics Measurements

A Frequency Response Method based on the infrared measurement of the sample temperature has been developed for adsorption kinetics measurements. It consists in modulating the experimental chamber volume at constant frequency. The complex ratio of the temperature response over the pressure response is independent of time but is a function of the frequency depending on all the kinetics parameters of the system. This method is accurate and allows to measure very fast kinetics. Its major drawback is that a spurious signal is observed at high pressure in absence of adsorption. The results obtained with silicalite-propane and NaX-carbon dioxide are compared with results obtained from other techniques (NMR, permeation, etc.).     

A Laser Flash Apparatus for Thermal Diffusivity and Specific Heat Capacity Measurements

We have developed a laser flash apparatus for simultaneous measurements of thermal diffusivity and specific heat capacity of solid materials by introducing recent technical progress: uniform heating by a homogenized laser beam using an optical fiber with a mode mixer, measuring transient temperature of a specimen with a calibrated radiation thermometer, analyzing a transient temperature curve with a curve fitting method, to achieve differential laser flash calorimetry. Thermal diffusivity, specific heat capacity and thermal conductivity of glassy carbon and molybdenum were measured in the temperature range from 300 to 1100 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Discrete pattern recognition by fitting onto a continuous function

This article outlines an original method for matching discrete structures when atom correspondences are unknown. This method avoids the current atom-by-atom treatment (and its inherent combinatorial problems) and considers the structures to be compared in their totality. The basic idea is to first obtain the atom correspondences by fitting one of the two discrete structures onto a spline approximation of the other, rather than optimizing in discrete space, and, second, to overlap the two discrete structures on the basis of the proposed assignment. As starting data, the method requires only the Cartesian coordinates of the two structures. No connectivity information, neither atom labeling nor matching tolerance is required. This method can readily handle matches of molecules with a few hundred atoms. It is able to search for a given 3D pattern as well as for a pattern common to two structures. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1875–1892, 1997     

Thermal Decomposition and Glass Transition Temperature Study of Poly-p-isopropylstyrene

Thermal decomposition and glass transition temperature studies have been carried out on poly-p-isopropylstyrene (PpiPrS) with a differential scanning calorimeter. The un-decomposed polymer as well as its decomposition products were analyzed by gel permeation chromatography (GPC), infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). During isothermal treatments in the 25–150°C temperature range (α < 3%), the observed increase in M arose primarily from interchain linking between the longer radical-bearing chains. Beyond 315°C (α > 6%), the molecular weight increases result from crosslinking reactions between decomposed polymer and longer undecomposed chains. During interchain linking, the number of isomethyl groups (iso-CH³) increase. In the crosslinking reactions that take place at temperatures beyond 315°C, the number of iso-CH³ and terminal or α-methyl groups (α-CH³) both increase while the number of methylene groups (CH²) decreases. Activation energies of decomposition for various homologs of polystyrene (PS) obey the following order: E_PS > E_PpiPrS > E_PpiPrαMeS ≥ E_PαMeS. A comparison of the Tg_e values of PS with those of PpiPrS, poly-α-methylstyrene (PαMeS) and poly-p-isopropyl-α- methylstyrene (PpiPrαMeS) shows that the presence of the p-isopropyl groups lowers the T_g of PS as well as that of PaMeS by about 30–35° K.     

Estimation of Critical Temperature of Thermal Explosion for Trinitromethyl Explosives by Non-isothermal DSC

Two general expressions and their six derived formulae for estimating the critical temperature(Tb) of thermal explosion for energetic materials(EMs) were derived from the Semenov’s thermal explosion theory and eight non-isothermal kinetic equations via reasonable hypothesis. We can easily obtain the values of the initial temperature(T0i) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of EMs, the onset temperature(Tei), the exothermic decomposition reaction kinetic parameters and the values of T00 and Te0 from the equation T0i or ei=T00 or e0+α1βi+α2βi2+···+αL–2βiL–2, i=1, 2, ···, L and then calculate the values of Tb by means of the six derived formulae. The results obtained with the six derived calculating methods for six trinitromethyl explosives: bis(2,2,2- trinitroethyl-N-nitro) ethylene diamine(BTNEDA), 2,2,2-trinitroethyl-4,4,4-trinitrobutyrate(TNETB), bis(2,2,2- trinitroethyl) formal(BNTF), bis(2,2,2-trinitroethyl-nitramine)(BTNNA), 2,2,2-trinitroethyl-2,2,2-trinitroethyl-N- nitroamino acetate(TNTNNA) and tetrakis [2,2,2-trinitroethyl] orthoester(TTNOE) agree well with each other.     

Measurements of Temperature and Electron Number Density in a dc Argon–Nitrogen Plasma Torch—Supersonic Operation

The diagnostics study on supersonic argon/nitrogen plasma jets expanded into a low-pressure test chamber is carried out by means of emission spectroscopy and enthalpy probe measurement techniques. The spatial distributions of electron density, temperatures, and associated shock structure effects in plasma jets are investigated in conjunction with their direct dependency upon the chamber pressure. The experimental results show the occurrence and the position of different zones; i.e., supersonic expansion, stationary shock waves and subsonic jet at pressures below 51 kPa. Flow fluctuations due to the oblique shock wave at 39 kPa background pressure are observed and discussed. The electron density profiles show variations along the plasma axis that coincide with the position of the shock waves. The experimental results show the transition from the moderately under-expanded to the strongly under-expanded jet structure induced by lowering of the chamber pressure.     

Debye Temperature Dependent Lattice Thermal Conductivity of Silicon

The temperature dependence of the Debye temperature θ_D(T) was applied to analyze the lattice thermal conductivity of Si between 2 and 300 K. The analysis of experimental data in terms of the Dubey model of the two modes of conduction has been carried out by combining the relaxation time for phonon-phonon scattering, point defect scattering and boundary scattering. The relative importance of the contribution of each mode was examined by estimating their percentage contribution to the phonon conductivity. Agreement between theory and experiment is achieved over the whole temperature range of study. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tomographic Measurements of Temperature Fluctuations in an Air Plasma Cutting Torch

A tomographic optical system and method based on evaluations of plasma radiation in a wavelength range of 559–601 nm were used to acquire temperature distributions in an air plasma cutting torch in planes perpendicular to the arc axis with a time resolution of 1 μs. The derived frequency spectra and distributions of temperature fluctuations represented by standard deviations have shown significant variations in distributions of instabilities, depending on the time scales which are taken into account. The results confirmed the decisive role of arc current ripple modulation in the arc temperature fluctuations.     

利用电流积分器和峰值保持单元改进固体电极上的多重峰测量和提高记录仪记录伏安图的精确性

本文推荐采用电流积分器和峰值保持(检测)器作为插入单元,以测量积分电量代替峰高测量,改进固体电极上的测量浓度范围。并采用峰值检测器提高记录仪的响应,使之适用于500～1000mV/s扫描速率下的伏安测定。本文以T(Ⅳ)作为例子证明上述优点。