时域反射光谱法研究酰胺-醇混合物的介电驰豫

Using time domain reflectometry (TDR),dielectric relaxation studies were carried out on binary mixtures of amides (N-methylformamide (NMF) and N,N-dimethylformamide (DMF)) with alcohols (1-butanol,1-pentanol,1-hexanol,1-heptanol,1-octanol,and 1-decanol) for various concentrations over the frequency range from 10 MHz to 10 GHz at 303 K. The Kirkwood correlation factor and excess dielectric constant properties were determined and discussed to yield information on the molecular interactions of the systems. The relaxation time varied with the chain length of alcohols and substituted amides were noticed. The Bruggeman plot shows a deviation from linearity. This deviation was attributed to some sort of molecular interaction which may take place between the alcohols and substituted amides. The excess static permittivity and excess inverse relaxation time values varied from negative to positive for all the systems indicating that the solute-solvent interaction existed between alcohols and substituted amides for all the dynamics of the mixture.     

时域反射谱法研究烷基丙烯酸酯与酚复合的介电弛豫

The dielectric relaxation measurements on binary mixtures of esters (methyl acrylate, ethyl acrylate, and butyl acrylate) with phenol derivatives (p-cresol, p-chlorophenol, and 2,4-dichlorophenol) were carried out at different concentrations at 303 K using the time domain reflectometry (TDR) over the frequency range from 10 MHz to 20 GHz. The Kirkwood correlation factor and excess inverse relaxation time were determined and discussed to yield information on the molecular interactions of the systems. The relaxation time increased with increasing concentration of phenols and increasing chain length of esters. The excess inverse relaxation time values were negative for all the systems, which indicated the solute-solvent interaction existing between esters and phenols producing a field in such a way that the effective dipole rotation was hindered.     

平面结构非均匀体系的介电驰豫—组成相的数目与电导对驰豫的影响

非均匀体系在０．１ｋＨｚ－１０ＭＨｚ频率范围显示出显著的介电驰豫，为了弄清介电驰豫的原因以及该驰豫与非均匀体系界面数目的关系，本文从介电的观点在理论及实验两方面讨论了典型的非均匀体系的例子：膜／溶液体系。特别地，对频率域的介电驰豫谱与组成相的结构及浓度的关系进行了分析，并在Ｍａｘｗｅｌｌ－Ｗａｇｎｅｒ机理的基础上现象论地解释了驰豫的原因，非均匀体系的介电驰豫性质具有下列特征：（１）介电驰豫数目等于     

VDF（81）／TeFE（19）共聚物的低温低频介电驰豫

用经过改进的介电驰豫谱仪测得不同结晶度的铁电共聚物ＶＤＦ（８１）／ＴｅＦＥ（１９）在－１２０－４０℃、１０＾－２－１０＾４－Ｈｚ范围内的复介电常数，低温介电驰豫过程显示室温以下共聚物的频率谱由低频和高频两两部分叠合而成，低频部分ＷＬＦ方程，收非晶区被冻结分子链段的微布朗运动贡献；高频部分遵从Ａｒｒｈｅｎｉｕｓ规律，由晶区和非晶区子链段较小尺度的局域运动产生，结果说明共聚物的玻璃化转化变温度是－５２     

介电松弛谱法用于高分子链动力学行为的研究

介电松弛谱法是研究高分子链松弛运动的一种有效方法.它可反映出分子的特征结构信息,对揭示高分子链动力学行为的本质及规律、调控其凝聚态结构意义重大.本文从介电松弛谱理论出发,总结出几种常用的介电特征参数以及用于解析这些参数的数学模型.通过介电松弛谱中高分子链的弛豫过程的解析,可得出与高分子链运动相关的特征参数,如介电常数、介电松弛强度以及链运动的特征松弛时间,从而判断链松弛运动的尺寸小大,松弛的基团以及链运动的协同过程;还可与Arrenius方程、Vogel-Tammann-Fulcher（VFT）方程、统计学模型建立联系,获得界面构造、分子内部组成、链动力学行为同环境的依存性等信息,为高分子材料的分子设计、开发与应用奠定高分子物理理论基础.     

1,2-聚丁二烯介电松弛的复平面分析

本文对1,2-聚丁二烯的介电松弛进行了复平面分析.结果表明,在1,2-聚丁二烯的玻璃化转变过程中,ε″(ω)与ε＇(ω)的关系满足Havriliak-Negami方程.由复平面图求出了样品的静态和光频下的介电系数,平均松弛时间和松弛时间分布参数.利用所得数据讨论了1,2-聚丁二烯在玻璃化转变过程中的构象变化、松弛时间分布和平均偶极矩等问题.     

平面结构非均匀体系的介电驰豫─—组成相的数目与电导对弛豫的影响

非均匀体系在０．１ｋＨｚ～１０ＭＨｚ频率范围显示出显著的介电弛豫,为了弄清介电弛豫的原因以及该弛豫与非均匀体系界面数目的关系,本文从介电的观点在理论及实验两方面讨论了典型的非均匀体系的例子：膜／溶液体系。特别地,对频率域的介电弛豫谱与组成相的结构及浓度的关系进行了分析,并在Ｍａｘｗｅｌｌ－Ｗａｇｎｅｒ机理的基础上现象论地解释了弛豫的原因。非均匀体系的介电弛豫性质具有下列特征：（１）介电弛豫数目等于体系内界面种类的数目;（２）特征弛豫频率紧密地依存于溶液相的电导。     

介观结构氮掺杂碳纳米笼负载铂-钌合金催化剂的优异甲醇电氧化性能

利用氮掺杂碳纳米笼（hNCNC）的高比表面积及掺杂氮原子的锚定作用,方便地将约3 nm的Pt-Ru合金纳米粒子均匀地负载在hNCNC表面,制得了Pt和Ru比例可调的Pt-Ru/hNCNC双金属合金催化剂.这些催化剂展现出优异的甲醇催化氧化活性和稳定性,且具有良好的抗CO中毒能力,显著优于Pt/hNCNC和商业PtRu/C等对照组催化剂.其优异的电化学性能可归因于以下因素的协同作用：（1） Pt-Ru合金的双功能机制增强了催化剂的CO氧化脱附能力从而使活性位重新暴露,（2） hNCNC的氮掺杂及高比表面积有利于获得粒径小且均匀的合金纳米粒子,（3） hNCNC的多尺度分级孔结构有利于甲醇等参与反应物质的传输.     

5-(5-氯-2-吡啶偶氮)-2,4-二氨基甲苯的电分析特性研究

本文采用多种电化学方法研究了5-Cl-PADAT的电分析特性,求得了该化合物的电极反应电子转移数,扩散系数及电极反应标准速率常数,研究了其在滴汞电极上的吸附性质,提出了可能的电极还原过程。并且应用光度法测定了化合物的酸离解常数。     

Complex Permittivity Spectra of Binary Pyridine–Amide Mixtures Using Time–Domain Reflectometry

Frequency spectra of the complex permittivity for pyridine–amide binary mixtures have been determined over the frequency range 10 MHz to 10 GHz, at 5, 15, 25, and 40°C, using the time–domain reflectometry method, for 11 compositions of each pyridine–amide system, e.g., formamide, N-methylformamide, and N,N-dimethylformamide. The relaxation in these systems can be described by a single relaxation time using the Debye model. The static dielectric constant, relaxation time, the corresponding excess dielectric properties, Kirkwood correlation factor, and molar activation energy of the mixtures have been determined. The excess permittivity is found to be positive in the amide-rich region and negative in the pyridine-rich region. The excess inverse relaxation time is negative, except in the pyridine-rich region. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model. The temperature-dependent relaxation times show the expected Arrhenius behavior.     

Microwave Dielectric Behaviour of 1,2‐Propanediol‐Water Mixture Studied Using Time Domain Reflectometry Technique

The dielectric behaviour of 1,2‐propanediol was investigated to understand the effect of the hydroxyl group on the dielectric parameters. The measurement of permittivity ?î and ?îî of 1,2‐propanediol was carried out in the frequency range 10 MHz to 20 GHz at 25 °C temperature. Static permittivity and dielectric relaxation time are extracted from a 1,2‐propanediol‐water mixture using the bilinear calibration method and non‐linear least squares fit method. Calculated Kirkwood correlation factor contains information regarding solute‐solvent interaction. The hydrogen bonded model suggested by Luzar is applied to determine the molecular parameters. The excess dielectric parameters and Bruggeman factor show the systematic change in the dielectric parameter of the system with change in concentration.     

Dielectric Study of n-Butyl Acetate–Alcohol Mixtures by Time-Domain Reflectometry

Using picosecond time-domain reflectometry (TDR), dielectric relaxation studies have been carried out on binary mixtures of n-butyl acetate with methanol, ethanol, and 1-propanol, over the frequency range from 10 MHz to 20 GHz, at various concentrations and temperatures. The excess permittivity, excess inverse relaxation time, Kirkwood correlation factor, and thermodynamic parameters have been obtained. The excess permittivity for all the systems is negative. The values of static permittivity and relaxation time decrease with an increase in the percentage of n-butyl acetate in the mixtures.     

Dielectric Study of Aqueous Solutions of Alanine and Phenylalanine

Dielectric relaxation measurements on aqueous solutions of alanine and phenylalanine were carried out using time domain reflectometry (TDR) at 25, 30, 35, and 40 °C in the frequency range from 10 MHz to 20 GHz. Aqueous solutions of alanine and phenylalanine are prepared for five different molar concentrations of the respective amino acid. For all the solutions considered, only one relaxation peak was observed in this frequency range. The relaxation peaks shift to lower frequency with an increase in alanine and phenylalanine molar concentration. The molar enthalpy of activation and molar entropy of activation show endothermic interactions.     

Dielectric Relaxation Studies of Binary Mixture of α‐Picoline and Methanol Using Time Domain Reflectometry at Different Temperatures

Complex permittivity spectra of binary mixtures of varying concentrations of α‐picoline and methanol (MeOH) were obtained using time domain reflectometry (TDR) technique over frequency range 10 MHz to 25 GHz at 283.15 K, 288.15 K, 293.15 K and 298.15 K temperatures. The dielectric relaxation parame‐ ters namely static permittivity (σ₀), high frequency limit permittivity (σ_oo1) and the relaxation time (ρ) were determined by fitting complex permittivity data to the single Debye/Cole‐Davidson model. Complex non linear least square (CNLS) fitting procedure was carried out using LEVMW software. The excess static permittivity (σ₀^E) and the excess inverse relaxation time (1/ρ)^E which contains information regarding mo‐ lecular structure and interaction between polar — polar liquids, were also determined. From the experimental data, effective Kirkwood correlation factor (g^eff) and Bruggeman factor (f_B) were calculated. Excess parameters were fitted to the Redlich‐Kister polynomial equation. The values of static permittivity and relaxation time increase non‐linearly with increase in the mol fraction of MeOH at all temperatures. The values of excess static permittivity (σ₀^E) and the excess inverse relaxation time (1/ρ)^E are negative for the studied α‐picoline — MeOH system at all temperatures.     

Temperature Dependent Dielectric Relaxation in Solvent Mixtures at Microwave Frequencies

By the use of time domain reflectometry method, dielectric measurements were carried out on dimethylformamide‐2‐nitrotoluene solvent mixtures in the frequency range 10 MHz‐20 GHz, at various temperatures from 15 °C to 45 °C. These solvent mixtures as well as pure solvents display a Debye type dispersion. Their frequency dependent dielectric properties can be summarized by the three parameters in the Debye equation: a static permittivity, permittivity at high frequency and a dielectric relaxation time constant. The free energy of activation for dipolar relaxation process and the Kirkwood correlation factor were determined using these fitting parameters for these solvent mixtures at various concentrations and temperatures. By using these dielectric parameters, the excess permittivity and excess inverse relaxation time is obtained. The excess permittivity is found to be positive for all concentrations and temperatures whereas the excess inverse relaxation time is negative.     

Dielectric Relaxation Study of Chloro Group with Associative Liquids. II. 1,2-Dichloroethane with Methanol, Ethanol, and 1-Propanol

Frequency spectra of the complex permittivity for 1,2-dichloroethane–alcohol binary mixtures have been determined over the frequency range 10 MHz to 20 GHz at 15, 25, 35, and 45°C, using the time-domain reflectometry (TDR) technique, for 11 compositions of each 1,2 dichloroethane–alcohol system. The alcohols used in the study were methanol, ethanol, and 1-propanol. The relaxation in these systems can be described by a single relaxation time using the Debye model. The static dielectric constant, relaxation time, the corresponding excess dielectric properties, Kirkwood correlation factor, and Bruggeman factor of the mixtures have been determined. The static dielectric constants for the mixtures have been fitted with the modified Bruggeman model.     

Dielectric relaxation and hydrogen bonding studies of chlorobutane-dioxane mixtures using a time domain technique

Complex permittivity spectra have been computed for the binary mixtures of Chlorobutane (CLB) with 1, 4-Dioxane (DX) using Time Domain Reflectometry (TDR) for different concentrations and temperatures in the frequency range from 10 MHz to 30 GHz. The static dielectric permittivity and relaxation time have been obtained by fitting complex permittivity spectra to the Debye relaxation using least squares fit method. The Kirkwood correlation factor have been determined at various concentrations of 1, 4-dioxane. The Bruggeman model for the non-linear case has been fitted to the dielectric data for the mixtures.