三乙酸甘油酯玻璃化转变的焓弛豫与介电弛豫研究

脆性较高的玻璃形成分子液体通常在焓弛豫和介电弛豫动力学上表现出明显的差异性, 为了深入理解这一问题, 本文针对具有较高液体脆性的三乙酸甘油酯对比研究了焓弛豫与介电弛豫行为. 利用这两个技术分别研究了结构弛豫动力学过程的非Arrhenius 与非指数特征, 液体脆性因子与非指数性因子的对比显示很好的一致性. 分析表明分子的柔性有可能对这两种弛豫过程中分子运动的相关性产生明显的影响. 讨论了玻璃形成液体的分子结构与动力学参数之间的关联.     

阴离子表面活性剂SDBS胶束溶液的介电弛豫行为

用射频介电谱方法研究了0.1-80 mmol·L-1浓度的十二烷基苯磺酸钠(SDBS)水溶液体系的介质弛豫行为. 测量发现频率接近107 Hz时, 在临界胶束浓度(CMC)附近出现显著的介电弛豫现象. 采用Cole-Cole函数拟合SDBS体系介电数据, 其拟合参数具有明显变化规律: 介电增量(△ε)随SDBS摩尔浓度(cs)的增加而增大, 表现为两种线性关系, 并在cs=36 mmol·L-1附近出现拐点; 特征弛豫时间(τ0)却在cs=45 mmol·L-1出现极小值. 利用胶束电模型分析了介电弛豫机制, 认为束缚Na+对离子数量和胶束体积变化是引起介电增量和特征弛豫时间变化的两个重要原因.     

NaA沸石离子交换过程的介电弛豫谱研究

在40 Hz~110 MHz频率段对不同Ca²⁺交换度的NaA沸石堆积体系进行了介电测量, 并利用Cole-Cole公式及Hanai方法对介电参数和相参数进行拟合与解析. 结果表明, 随着Ca²⁺交换度的不断增高, 堆积体系的介电增量、弛豫频率、弛豫分布系数以及粒子的电导率均有不同程度的降低, 而粒子的介电常数保持不变. 通过综合分析弛豫变化规律与离子交换度的内在联系发现, 离子交换后Ca²⁺选择六元环占位, 同时六元环和八元环位置的相邻2个Na⁺被置换; 占据六元环的Ca²⁺与八元环位置的Na⁺对沸石粒子的极化贡献等价; Ca²⁺的进入导致沸石孔道内微观电场多样化.     

水/乙醇/正辛醇无表面活性剂微乳液的介电弛豫谱

无表面活性剂微乳液近年来受到人们极大关注,但人们对该类微乳液体系的了解还不够深入,在许多基础问题上仍存在较大争议,因此十分有必要利用不同的技术手段对该类体系开展研究.介电谱是表征微乳液体系的有效方法之一,但在无表面活性剂微乳液体系中的应用还鲜有报道.根据水/乙醇/正辛醇所组成的三元体系相图,选取了 3条路径配制了不同相...     

离子交换树脂悬浊液的介电弛豫谱研究

研究了D354阴离子交换树脂分散在不同浓度KCl溶液中的悬浊液的频率域介电谱,发现在测量频率为106～107 Hz处出现了显著的介电弛豫现象,得出了介电常数、电导率以及弛豫时间随KCl溶液浓度的特异的变化关系,理论分析表明,该弛豫是一个以界面极化为主的非单一极化机制的弛豫过程,进而利用Maxwell-Wagner界面极化理论和双电层性质解释了该体系的特异介电行为,得到了树脂悬浊液在外加交变电场下的离子迁移和聚集信息,并确定了该树脂在静态平衡下双电层中对离子的相对离子强度.     

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.     

马来二腈基二硫烯镍（Ⅱ）配合物展现了介电反常和弛豫

合成并用X-射线单晶衍射表征了一个离子对化合物1,7-bis（1-methylimidazolium）heptane bis（maleonitriodithiolato）nickelate（1）的结构。沿着晶体学c轴方向,化合物1中的阴、阳离子分别排列形成波浪形的链。变温介电性质研究表明,化合物1在90℃左右展现了介电态转变。我们将此转变归于化合物1中平衡阳离子的有序到无序转变。在低频区,化合物1出现了明显的介电弛豫过程,这与阳离子偶极运动有关。此外,DSC研究表明,在第二个升温过程中,化合物1在66℃和130℃左右出现两步冷结晶。此种冷结晶现象在小分子化合物中很罕见,这与化合物1的较大粘度以及测试过程中的较快降温速率有关。     

马来二腈基二硫烯镍(Ⅱ)配合物展现了介电反常和弛豫

合成并用X-射线单晶衍射表征了一个离子对化合物1,7-bis(1-methylimidazolium)heptane bis(maleonitriodithiolato)nickelate(1)的结构。沿着晶体学c轴方向,化合物1中的阴、阳离子分别排列形成波浪形的链。变温介电性质研究表明,化合物1在90℃左右展现了介电态转变。我们将此转变归于化合物1中平衡阳离子的有序到无序转变。在低频区,化合物1出现了明显的介电弛豫过程,这与阳离子偶极运动有关。此外,DSC研究表明,在第二个升温过程中,化合物1在66℃和130℃左右出现两步冷结晶。此种冷结晶现象在小分子化合物中很罕见,这与化合物1的较大粘度以及测试过程中的较快降温速率有关。     

PS-PBA粒子分散系的介电弛豫谱解析——同、反离子对弛豫的影响及表界面电参数的计算

制备了近纳米级的聚苯乙烯-丙烯酸丁酯(PS-PBA)复合微球粒子,并在40Hz～110×106Hz的宽频范围测量了该粒子分散在9种电解质中时的介电弛豫谱,发现了与PS微球粒子分散系不同的特异介电弛豫:低频弛豫对反离子种类具有敏感性而高频弛豫则与电解质种类几乎无关;根据Shilov-Dukhin模型和M-W-O模型分别分析了高、低频率的弛豫机制,并通过对介电谱的Cole-Cole拟合获得了各体系的介电参数.进一步利用Hanai方法由介电参数计算获得了所有体系的相参数;详细分析了体系的内部参数受PS-PBA微球自身结构以及电解质种类影响的原因;讨论了离子扩散系数对介电参数的影响,从而得出了低、高频的弛豫特征时间分别由同离子的扩散系数和反离子的扩散系数所决定之结论.最后,结合Grosse宽频介电理论计算了粒子表面的以及双电层的主要电参数,并分析了电解质种类差异对这些电参数的影响.     

球壳粒子悬浮系模型化研究——内部相参数对介电谱影响的数值模拟

在Hanai理论基础上对球壳粒子悬浮系的介电模型进行了模拟研究,通过用C++的复数类对理论公式的程序化,建立了介电谱的介电参数与体系内部相参数的关系.所得的解析解可方便地模拟介电弛豫谱依不同相参数的变化曲线,计算并分析了内部参数对介电谱的模式以及介电参数的影响因素.     

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 carded 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.     

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.     

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 of Aqueous Trimethylamineoxide Solutions

Dielectric relaxation was examined for aqueous trimethylamineoxide (TMAO) solutions over a wide concentration (c) range. The dielectric relaxation of TMAO was described by a Debye-type function with a relaxation time of about 3 × 10^–11 s, with the strength proportional to c. The number of water molecules tightly hydrated to unprotonated TMAO was estimated to be two. Ab initio calculations predict the magnitudes of the dipoles for individual TMAO and TMAO tightly hydrated by two water molecules, to be 4.9 and 4.2 D, respectively. When the amount of HBr added was increased, dielectric spectra were described by two modes with relaxation times, about 3 × 10^–11 and the about 8 × 10^–10. The fast relaxation was assigned to the rotational mode of unprotonated TMAO tightly hydrated by two water molecules, and the slow mode to the rotational mode of dimers formed between a protonated and unprotonated TMAO due to hydrogen bonding.     

醇与丙烯酸酯的介电弛豫性质

Acrylic esters are industrially important chemicals, which are used as adhesives, paints, binders, and emulsifiers[1]. Alcohols play an important role in many chemical reactions because of their ability to undergo self-association with manifold internal s…     

Hydrogen-Bond Structure and Low-Frequency Dynamics of Electrolyte Solutions: Hydration Numbers from ab Initio Water Reorientation Dynamics and Dielectric Relaxation Spectroscopy

We present an atomistic simulation scheme for the determination of the hydration number (h) of aqueous electrolyte solutions based on the calculation of the water dipole reorientation dynamics. In this methodology, the time evolution of an aqueous electrolyte solution generated from ab initio molecular dynamics simulations is used to compute the reorientation time of different water subpopulations. The value of h is determined by considering whether the reorientation time of the water subpopulations is retarded with respect to bulk-like behavior. The application of this computational protocol to magnesium chloride (MgCl₂) solutions at different concentrations (0.6–2.8 mol kg⁻¹) gives h values in excellent agreement with experimental hydration numbers obtained using GHz-to-THz dielectric relaxation spectroscopy. This methodology is attractive because it is based on a well-defined criterion for the definition of hydration number and provides a link with the molecular-level processes responsible for affecting bulk solution behavior. Analysis of the ab initio molecular dynamics trajectories using radial distribution functions, hydrogen bonding statistics, vibrational density of states, water-water hydrogen bonding lifetimes, and water dipole reorientation reveals that MgCl₂ has a considerable influence on the hydrogen bond network compared with bulk water. These effects have been assigned to the specific strong Mg-water interaction rather than the Cl-water interaction.     

An Electric Criterion to Evaluate Glass Transition Temperature: Dielectric Relaxation Measurements

In this contribution, a dielectric measurement technique for the evaluation of phase transition temperature and the study of physical aging on polymeric thin films is considered. This kind of measurement provides the possibility of displaying phase transitions with a high degree of precision. Furthermore, it can be considered alternatively to techniques not applicable in the case of thin films, such as Differential Scanning Calorimetry (DSC). In this work, owing to the high sensitivity of the utilized experimental set-up, a glass transition T_G of 156 K, with a precision equal to 0.3%, and a melting T_M = 220 K have been assessed for 4 µm thick Polydimethylsiloxane (PDMS) films. Performing measurement as a function of time, it was possible to monitor physical aging phenomena, mainly consisting in a change of dielectric properties. As expected, the time evolution of the aging phenomena can be described by a simple logarithmic law.     

Relaxation of quantum hydrodynamic modes

In this article, we develop a series of hierarchical mode‐coupling equations for the momentum cumulants and moments of the density matrix for a mixed quantum system. Working in the Lagrange representation, we show how these can be used to compute quantum trajectories for dissipative and nondissipative systems. This approach is complementary to the de Broglie–Bohm approach in that the moments evolve along hydrodynamic/Lagrangian paths. In the limit of no dissipation, the paths are the Bohmian paths. However, the “quantum force” in our case is represented in terms of momentum fluctuations and an osmotic pressure. Representative calculations for the relaxation of a harmonic system are presented to illustrate the rapid convergence of the cumulant expansion in the presence of a dissipative environment. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002