Dielectric relaxation behavior of SDS/β-CD organized self-assembly in dilute aqueous solution

Dielectric relaxation behavior of SDS/β-CD self-organized with mass concentrations from 1% to 7% was investigated. The phase microstructure of SDS/β-CD aqueous solution was confirmed by analyzing the dielectric parameters. The dielectric relaxation behavior was attributed to the interfacial polarization between vesicle and medium, and the relaxation distribution parameter can indicate the shape transition from vesicles to microtubules with increasing concentration. Dielectric relaxation provided a new method to study surfactant organized self-assembly.     

膜/液界面浓度极化现象的介电解析

对由强、弱荷电膜和溶液构成的膜／液非均匀体系，在10－107Hz频率范围进行了介电测量，在直流偏压下，该体系显示了二个显著的介电弛豫．利用具有电导率分布相，即浓度极化相的介电理论对强行电的离子交换膜的结果进行了介电解析，从实验上测得的介电参数求出了反映膜／液界面浓度极化层构造的参数，讨论了该体系产生介电弛像的原因、说明了介电理论的合理性，并提出了膜／液界面体系产生介电弛豫现象的可能机理．     

Beyond the first hydration shell: dielectric study of LiCl aqueous solution

The dielectric constant for lithium chloride (LiCl) in aqueous solution with the entire concentration has been determined in the frequency range 0.5 GHz–50GHz at 298 K by dielectric relaxation spectroscopy (DRS). The system behaviour is described according to the Cole–Cole and two Debye-type relaxation functions whose evolution with composition is analysed. Combining the Cole–Cole and two Debye-type relaxation functions, the results of the dielectric properties of aqueous LiCl solution are presented and discussed. The maximum number of water molecules perturbed by ions in the hydration shell decays with its concentration. Using the extended Froehlich theory, it is concluded that the water structure is perturbed by ions beyond the first hydration shell in LiCl aqueous solution system.     

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。     

Dielectric relaxation study of aqueous α-amylase using time domain reflectometry technique

Time domain reflectometry technique has been used to study the complex permittivity spectra of aqueous α-amylase solution at different pH. Static dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least square fit method. The dielectric relaxation parameter increases with an increase in molar concentration of α-amylase in water due to the formation of hydrogen bonding. The hydration numbers were also determined from the static dielectric constant.     

聚吡咯微粒掺入的聚苯乙烯膜在电解质溶液中的介电弛豫谱及其解析

在40 Hz～11 MHz频率范围测量了聚苯乙烯膜以及混入聚吡咯粒子的聚苯乙烯膜和电解质溶液构成的体系的介电谱, 发现了特异的弛豫现象: 纯的和掺入导电性聚吡咯后的聚苯乙烯膜分别显示出单一弛豫和双弛豫的不同模式的介电谱. 在Maxwell-Wagner界面极化概念基础上解释了该弛豫机制: 高、低频弛豫分别由膜-液界面极化和膜相本身的不均一性引起的. 将体系进行了模型化, 并利用Hanai理论方法对谱进行了解析, 获得了内部电性质的诸多参数. 对不同聚吡咯掺入量的膜/溶液体系的介电测量和解析结果表明, 电解质溶液的种类、浓度以及膜中混入聚吡咯的量都影响着膜相的介电响应. 这些结论为利用加入导电粒子改善绝缘高分子聚合物的电性质的研究以及制备既具有导电功能又使基体的力学性能得到提高的高分子复合物提供了重要的线索.     

Analysis of dielectric observations of KCl-charged poly(methyl methacrylate) microcapsules using a two-component model consisting of KCl-permeable and KCl-impermeable capsules

Dielectric measurements were carried out on aqueous suspensions of poly(methyl methacrylate) microcapsules charged with KCl solutions to examine the KCl permeability of the microcapsules. The specimens exhibited three kinds of dielectric relaxation. Two kinds of dielectric relaxation were observed immediately after washing the specimens with distilled water. These overlapped each other when the specimen was left standing in the measuring cell for a long time. Their relaxation frequencies were affected by the KCl concentration of the suspending medium in which the specimen was kept before washing. Another relaxation was observed distinctly when the spepcimens were washed thoroughly with distilled water. Its relaxation frequency was affected by the KCl concentration of the charged solution. These results were explained by assuming that the specimens were mixtures of KCl-permeable and KCl-impermeable capsules. The theoretical analysis procedure was devised in the light of dielectric theory of interfacial polarization to estimate the parameters which characterize the structure of the specimens.     

反渗透膜UTC-70在水溶液中的介电谱及其解析

根据平面层状体系介电弛豫理论研究了反渗透膜UTC-70在各种浓度氯化钠和氯化钾溶液中的介电弛豫行为.利用计算机拟合的方法得到膜/溶液体系的介电参数,并由此计算得到了UTC-70膜相和水溶液相的相参数,获得了反映反渗透膜UTC-70荷电情况的信息及其与电解质溶液浓度的关系,介电解析的结果解释了介电弛豫的产生机制.     

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.     

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.     

非导电微球悬浊系的介电谱——弛豫机制的考察和界面信息的解析

研究了不同浓度电解质溶液中聚苯乙烯微球悬浊液的介电谱, 发现在40 Hz～110 MHz频率范围内出现了两个明显的弛豫. 在介电模型基础上对弛豫原因的理论分析结果表明, 千赫兹频域出现的弛豫是由粒子附近双电层中对离子的扩散所致, 兆赫兹附近出现的弛豫源于空间电荷在固/液界面的累积. 应用Hanai方法计算出体系内部的相参数, 获得了微球/溶液界面的电信息, 并给出了合理解释. 理论计算结果验证了模型和方法的适用性. 实验采用透析法调制样品, 有效地防止了体系内部粒子二次团聚的发生.     

Measurement of the dielectric relaxation property of water-ion loose complex in aqueous solutions of salt at low concentrations

Electrolytes and their dissociated ions are thought to form positive or negative hydration layers around them. In this study, we have developed a method to determine the volume and the dielectric relaxation property (relaxation frequency f c, dispersion intensity delta) of the water hydrating ions in salt solutions. The method consists of four steps: (1) By use of a high-resolution microwave dielectric spectroscopy technique, the dielectric spectra of sample salt solution and bulk water are measured in pair. (2) The dielectric spectrum of solutes (ions) with water layers for a given volume fraction varphi is then calculated from each pair of dielectric spectra of a sample salt solution and reference water according to the Hanai mixture theory. (3) Each spectrum of solutes with water layers at a given varphi is decomposed into a few Debye relaxation functions and the bulk water component. (4) The volume fraction varphi is operationally decreased from 0.5, and steps (2) and (3) are repeated at each varphi until the bulk water component vanished. Then the volume fraction of the hydrated solutes (ions) in solution is determined. The method was applied to NaF and NaCl solutions. As a result the different spectral intensity was nearly proportional to the salt concentration below 0.2 M in the frequency range of 3-26 GHz. The hydration number N h and the dielectric relaxation property of the hydration layer for each salt solution was successfully determined as ( f c1, delta 1, N h)= (18.7, 44.9, 27.9) for NaCl and ( f c1, delta 1, f c2, delta 2, N h) = (26.0, 6.70, 5.64, 19.2) for NaF.     

Dielectric relaxation studies of binary mixtures of N-methylacetamide and N-methylformamide in benzene solutions using microwave absorption data

Using standard microwave X-band technique and by following Gopala Krishna's single frequency (9.90?GHz) concentration variational method, the dielectric relaxation times (τ) and the dipole moments (μ) of dilute solution of N-methylacetamide (NMA), N-methylformamide (NMF) and NMA?+?NMF binary mixtures in benzene solutions have been calculated at different temperatures. The energy parameters for the dielectric relaxation process for NMA?+?NMF binary mixture containing 30?mol% NMF have been calculated at 25, 30, 35 and 40°C and compared with the corresponding viscosity parameters. A good agreement between the free energy of activation from these two sets of values shows that the dielectric relaxation process like the viscous flow process can be treated as the rate process. From relaxation time behavior of NMA and NMF binary mixture in benzene solution, solute–solute types of the molecular association has been proposed.     

Dielectric relaxation in concentrated solutions of poly(γ-benzyl-L-glutamate)

Measurements of dielectric constant and loss, broad-line nuclear magnetic resonance, and differential thermal analysis of concentrated solutions of poly(γ-benzyl-L -glutamate) (PBLG) were carried out to determine the effects of intermolecular interactions on the mobility of the side group and the solvent (dichloromethane or dioxane). Only one dielectric loss peak due to the cooperative motion of the side group and the solvent was found. The activation energy of this relaxation process varied from 3 to 47 kcal/mole with increasing concentration of PBLG from 20 to 100% by weight accompanied with steep increases at about 40 and 80%. This result is explained as due to entanglement of neighboring side groups. In NMR, narrowing of the line was observed near the temperature where the dielectric loss was observed. The glass transition was also observed by differential thermal analysis. From these results it was concluded that the relaxation observed in PBLG solution and in pure PBLG have the nature of primary or α relaxations.     

Dielectric relaxation behavior of colloidal suspensions of palladium nanoparticle chains dispersed in PVP/EG solution

Dielectric measurements were carried out on colloidal suspensions of palladium nanoparticle chains dispersed in poly(vinyl pyrrolidone)/ethylene glycol (PVP/EG) solution with different particle volume fractions, and dielectric relaxation with relaxation time distribution and small relaxation amplitude was observed in the frequency range from 10(5) to 10(7) Hz. By means of the method based on logarithmic derivative of the dielectric constant and a numerical Kramers-Kronig transform method, two dielectric relaxations were confirmed and dielectric parameters were determined from the dielectric spectra. The dielectric parameters showed a strong dependence on the volume fraction of palladium nanoparticle chain. Through analyzing limiting conductivity at low frequency, the authors found the conductance percolation phenomenon of the suspensions, and the threshold volume fraction is about 0.18. It was concluded from analyzing the dielectric parameters that the high frequency dielectric relaxation results from interfacial polarization and the low frequency dielectric relaxation is a consequence of counterion polarization. They also found that the dispersion state of the palladium nanoparticle chain in PVP/EG solution is dependent on the particle volume fraction, and this may shed some light on a better application of this kind of materials.     

Dielectric Analysis of Dynamic Fouling Behavior on Surface of Polyethersulfone Composite Ultrafiltration Membrane

A dielectric analysis model for the fouling layer on the polyethersulfone composite ultrafil-tration (UF) membrane and solution system, which consists of the solution, concentration polarization layer (CPL), and cake layer, was established by virtue of the interfacial polar-ization and the electrostatic field theory. The effect of some important parameters, such as the depth, conductivity of CPL, and cake layer, on the dielectric spectroscopy (or dielectric relaxation properties) of the UF system was discussed by the parameter sensitivity analy-sis and the dielectric measurement. The simulations indicate that the CPL can be created rapidly and the cake layer formation is the dynamic balance process of growth and erosion in the process of UF. The key factor affecting on the dielectric spectrum of UF system is the electrical properties of the CPL and the cake layer. In comparison to the results of dielectric measurement, the simulations indicate that the model proposed in this work is valid and reliable to some degree for describing and explaining the dielectric relaxation phenomenon in UF system. It is very important to further understand the fouling behavior of membrane surface and optimize the controlling techniques of membrane fouling in the process of UF.     

Dielectric relaxation study of glycine–water mixtures using time domain reflectometry technique

The complex permittivity of glycine in water mixture for various temperatures and concentrations have been measured as a function of frequency between 10?MHz and 30?GHz using time domain reflectometry technique. Dielectric parameters, i.e. static dielectric constant and relaxation time were obtained from the complex permittivity spectra using nonlinear least square fit method. The dielectric relaxation parameter increases with an increase in molar concentration of glycine due to the formation of hydrogen bond groups by glycine molecule in an aqueous solution medium. The activation entropy, activation enthalpy and Kirkwood correlation factor have also been determined for glycine–water mixtures.     

High-Frequency Dynamical Behavior of Poly(ethylene glycol)+H2O Mixtures by Brillouin Spectroscopy

Brillouin spectroscopy has been used to examine high-frequency dynamical behavior of aqueous solutions of poly(ethylene glycol) (Mw ≈ 400g/mol) at 298K in the entire concentration region. It was found that a relaxation process takes place in the experimental frequency window that significantly affects the shape of experimentally recorded spectrum of the density fluctuations (dynamical structure factor). The process detected was attributed to segmental motion of the flexible polymeric chain. The full spectrum analysis of Brillouin spectra has been performed taking advantage of the relaxation function previously used in describing a single relaxation process in dielectric examination of water solutions of PEG 400. The proposed data processing procedure permits a qualitative reproduction of concentration dependencies of the hypersonic wave velocity and absorption measured. The shapes of the concentration dependencies of the relaxation times obtained from the Brillouin and the dielectric spectroscopies are in good agreement over a very broad concentration range, although their absolute values are scaled by the factor of 3. This result indicate that the two processes revealed independently by dielectric and Brillouin spectroscopies, apparently separated in time-scale, are just the same relaxation process.     

聚吡咯/聚苯乙烯混合膜/电解质溶液体系的介电谱解析电解质种类和浓度对膜透过性的影响

测量了混入聚吡咯粒子的聚苯乙烯混合膜在不同浓度的氯化钠、氯化钾、氯化钙及氯化镁体系的介电谱, 在40 Hz~11 MHz, 发现了显著的双介电弛豫现象(Double-relaxation phenomena). 基于Maxwell-Wagner理论讨论了弛豫产生的机制, 将体系进行了模型化, 并利用Hanai理论方法对介电谱进行了解析, 从获得的内部参数对混合后的膜荷电性质以及混合膜对离子的透过性进行了详细的讨论, 进而利用Donnan平衡理论推导的膜电位的表达式拟合, 获得了混合膜的固定电荷等参数.     

Phases confirmation of cloudy Silwet L-77 aqueous solution by dielectric relaxation spectroscopy

<正>The phase transition of Silwet L-77(a kind of siloxane surfactant) dilute aqueous solution with temperature was investigated by dielectric relaxation spectroscopy.In the initial heating process,a dielectric relaxation was found at about 10~6 Hz,which was considered as the interface polarization ascribed to the interface between water and liquid phases(W and L_1).With the temperature increasing further,a new dielectric relaxation was observed at about 10~4 Hz,which was assigned to the appearance of liquid crystal phase(L_α).According to the dielectric parameters fitted by Cole-Cole equation,the coexistence temperature of W,L_1 and L_αwas determined at about 37.0℃.