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.     

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.     

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。     

聚醚聚氨酯双离子型离聚物的介电性能研究

以4,4＇-二苯基甲烷二异氰酸酯(MDI)、N-甲基二乙醇胺(MDEA)和聚四氢呋喃(PTMD)以2:1:1(mol比)合成聚醚型聚氨酯,MDEA的叔胺基与γ-丙磺内酯反应,制备了不同磺化程度的双离子型离聚物.在不同温度与频率(-150-30℃,20Hz—100KHz)下,测定了其介电性能.结果表明,随离子化程度的提高,ε＇增大,α弛豫介电损耗峰移向低温,说明相分离越趋完善;β弛豫单元的活化能(△Hβ)基本不变;α弛豫单元的活化能(△Hα)依次变小.介电测量结果与动态力学方法研究结果相吻合.     

两端系留纳米粒子聚合物的分子动力学模拟

两端系留纳米粒子聚合物是研究末端对聚合物链弛豫行为影响的优选分子模型.本文构建了两端系留纳米粒子聚合物模型,运用粗粒化分子动力学方法研究了两端系留纳米粒子聚合物的特征温度和弛豫行为,探讨了纳米粒子半径和聚合物链长对玻璃化转变温度、结晶温度和介电性能的影响.研究表明,聚合物两端纳米粒子的存在可延缓聚合物链的弛豫并促进结晶,使两端系留纳米粒子聚合物的玻璃化转变温度和结晶温度均增加.研究结果与相关的实验报道吻合,可加深对两端系留纳米粒子聚合物结构和性能的理解.     

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.     

壳聚糖微球悬浊液的介电谱研究:弛豫机制的解释和内部信息的获得

结合DLVO理论和壳聚糖微球的特点, 提出了适合实验数据的电动力学模型, 并分析了浓厚分散系的界面极化弛豫的微观机制. 进而测量了不同粒径壳聚糖微球悬浊液的介电谱, 发现在10～100 MHz频率范围内均出现明显的介电弛豫现象. 利用上述模型合理解释了该弛豫现象以及微球粒径对界面极化弛豫的影响, 结果也证明了我们提出的模型的适当性. 此外, 利用Hanai方法, 通过介电参数准确计算出了各悬浊液的内部信息, 并且分析了这些实时信息的合理性. 研究结果从实验和理论两方面展示了介电谱方法在即时获取壳聚糖内部信息上的独到优势.     

非导电球型粒子悬浮液宽频介电谱——薄双电层理论的计算机模拟

以Shilov等提出的带有紧密层表面电导率的非导电球型粒子悬浮液宽频介电弛豫的薄双电层理论为基础, 从电动力学角度解释了粒子分散系两种典型介电弛豫(高频和低频弛豫)的机制. 在此基础上, 利用Mathcad程序将该理论定量程序化并建立了粒子/水相分散系介电谱参数与体系内部相参数的关系. 进而利用该程序模拟了溶液浓度、Zeta电位以及分散粒子半径等内相参数对两种弛豫的影响, 结合该理论阐述了不同环境下这两种弛豫的变化规律, 从而为今后更好地利用这两种弛豫表征纳米至毫米级球形粒子分散系的各相电及界面性质提供了有价值的参考.     

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.     

掠射椭圆偏振谱学方法数理模型的研究

掠射椭圆偏振谱学方法通过现场测量椭圆偏振参量Δ和Ψ能够反映电极过程的性质及变化规律.将电化学反应中的扩散层模型与掠射椭圆偏振实验体系相结合,提出了掠射椭圆偏振谱学方法的数理模型,对掠射椭圆偏振参量Δ和Ψ的物理化学意义做出了解释,认为电极表面附近的溶液扩散层对于椭圆偏振光既有相位延迟器的作用,又有振幅吸收器的作用；并应用一些实验结果,分析了电解液中电活性物质浓度和入射光束斑直径对掠射椭圆偏振参量的影响.     

Use of a cooperative-motion domain model to analyze brillouin light scattering measurements of the dynamic modulus in triblock copolymers

The use of the relaxation function is widespread in the study of polymer dynamics. Since the popular empirical KWW relaxation function consistently underestimates dielectric loss at high frequency, several models dealing explicitly with intermolecular cooperativity have been proposed as alternatives. In this article, the domain model proposed by Matsuoka, previously used only to analyze dielectric relaxation results, is used to analyze Brillouin light scattering results from polystyrene–polybutadiene–polystyrene triblock copolymers. A single relaxation time analysis and the KWW model are both compared to the domain model. Neither of these models fits the Brillouin data well. The single relaxation time analysis gives a physically unrealistic results; the KWW analysis fits the data at low frequency, but fails in the high-frequency region by underestimating the attenuation. The domain model fits the Brillouin data well over the entire temperature/frequency range. The results show that in order to understand the full range of dynamics in these materials and in polymeric materials in general, the KWW model is insufficient due to its underestimation of attenuation at high frequency. A model including cooperative motion is crucial to fully understand polymer dynamics. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2170–2178, 2000     

Interpretation of the TSDC fractional polarization experiments on the α‐relaxation of polymers

We report on the interpretation of the thermally stimulated depolarization current (TSDC) experiments, with partial polarization methods, on the dielectric α‐relaxation. The results obtained on polyvinyl acetate are rationalized on the basis of the Boltzmann superposition principle in combination with a Kohlrausch–Williams–Watts (KWW) time decay of the polarization (with the β exponent essentially temperature independent and equal to the value determined by conventional dielectric methods at T_g). From this analysis of the global TSDC spectrum we found a complex temperature dependence of the KWW relaxation time, which is Arrhenius‐like at the lowest temperatures but crosses over to the Vogel–Fulcher behavior observed above T_g in the temperature range of the TSDC peak. On the basis of these results, we found the way of predicting the TSDC spectra measured after partial polarization procedures. We found that, the distribution of activation energies and compensation behavior deduced by following the standard way of analysis are associated to the assumption of an Arrhenius‐like temperature dependence of the α‐relaxation time in the temperature range explored by TSDC. Therefore we conclude that both the distribution of activation energies and compensation behavior obtained by following the standard way of analysis do not give a proper physical picture of the α‐relaxation of glassy polymers around the glass‐transition temperature. Our results also show that the partial polarization TSDC methods are not able to give insight about the actual existence or not of a distribution of relaxation times at the origin of the nonexponentiality of the α‐relaxation of polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2105–2113, 2000     

Effects of the volume and temperature on the global and segmental dynamics in poly(propylene glycol) and 1,4‐polyisoprene

Published dielectric relaxation measurements for poly(propylene glycol) and 1,4‐polyisoprene are analyzed to determine the relative effects that thermal energy and volume have on the temperature dependence of the normal‐mode relaxation times, and these are compared with their effects on the temperature dependence of the local segmental relaxation times. For both polymers at temperatures well above the glass‐transition temperature, both relaxation modes are governed more by the thermal energy than by the volume, although the latter's contribution is not negligible. Such a result is consistent with an assumption underlying models for polymer viscoelasticity, such as the Rouse and tube models, that the friction coefficient governing motions over large length scales can be identified with the local segmental friction coefficient. Moreover, the relaxation data for both the segmental and normal modes superimpose when expressed as a function of the product of the temperature and volume, the latter being raised to a power. This scaling form arises from an inverse power law for the repulsive part of the intermolecular potential. The value of the exponent on the volume is the same for the normal and segmental motions and for both polymers indicates a relatively soft potential. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4313–4319, 2004     

Strain and temperature accelerated relaxation in polycarbonate

The nonlinear viscoelastic behavior of glassy polymers and its relationship to ductile yielding is studied by single- and double-step stress relaxation experiments. In the latter case a small stress relaxation step is superimposed on a specimen at an elevated state of temperature or strain. The results show that the changes in the relaxation behaviors in the two cases closely parallel each other. The relaxation behavior at strains near yield closely approximates that at low strain but near Tg. The small strain relaxation response can be described well by a Kohlrausch-Williams-Watts (KWW) type function. The interpretation of these data in terms of a coupling model which includes the KWW form is discussed.     

Dynamic light scattering from bulk poly(n-hexylmethacrylate) near and above the glass transition

Photon correlation spectra of polarized scattered light from poly(n-hexylmethacrylate) PHMA (M_w = 1.6·10⁵, T_g = ?5°C) have been studied in the temperature range of ?2–25°C. The experimental time correlation functions over the time range 10^?6?10² s were represented by the Kohlrausch-Williams-Watts (KWW) function exp{?(t/τ)^β} with a virtually temperature-independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass-rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass-rubber or α-relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10^?6 s near T_g. © 1992 John Wiley & Sons, Inc.     

Photon correlation spectroscopy of bulk poly(n-hexyl methacrylate) near the glass transition

Slowly relaxing longitudinal density fluctuations in an optically perfect sample of bulk poly(n-hexyl methacrylate) (PHMA) have been studied by photon correlation spectroscopy in the temperature range 10–36°C. The glass transition temperature for this sample was measured to be T_g = −3°C by differential scanning calorimetry. The optical purity of the sample was verified by Rayleigh-Brillouin spectroscopy and the Landau-Placzek ratio was observed to be 2.3 at 25°C. Light-scattering relaxation functions were obtained over the time range 10⁻⁶-1 s. The shape of the relaxation functions broadened as the temperature was lowered towards the glass transition. Quantitative analysis of the results was carried out using the Kohlrausch-Williams-Watts (KWW) function to obtain average relaxation times, 〈τ〉, and width parameters, β. The width parameter decreased from 0.43 to 0.21 over the temperature interval, as suggested by visual inspection. Average relaxation times shifted with temperature in a manner consistent with previous mechanical studies of the primary glass-rubber relaxation in PHMA. The relaxation functions were also analyzed in terms of a distribution of relaxation rates, G(Γ). The calculated distributions were unimodal at all temperatures. The average relaxation times obtained from G(Γ) were in agreement with the KWW analysis, and the shape of the distribution broadened as the sample was cooled. The rate at which G(Γ) displayed a maximum correlated well with the corresponding frequency of maximum dielectric loss for PHMA. The temperature dependence of these two quantities could be reproduced with an Arrhenius activation energy of 21 Kcal/mol. A consistent picture of the molecular dynamics of PHMA near the glass transition requires a strong secondary relaxation process with a different temperature dependence from the primary glass-rubber relaxation. The present results suggest that the behavior of PHMA is similar to the other poly(alkyl methacrylates). © 1996 John Wiley & Sons, Inc.     

Dielectric properties of bisphenol-a epoxy resins

The α-relaxation process of seven commercial diglycidyl ether of bisphenol-A (DGEBA) epoxy resins of varying molecular weights, without hardener, was characterized by measuring the frequency and temperature dependence of the complex permittivity, (?ast;). The temperature dependences of the frequency of maximum dipole loss ?_max and the ionic conductivity σ are non-Arrhenius and can be described by the Williams-Landel-Ferry (WLF) equation. The frequency dependence of the molecular relaxation process is described by the Kohlrausch-Williams-Watts (KWW) relaxation function. The WLF C₁ parameter and the KWW β parameter, describing the temperature and frequency dependences, respectively, vary systematically with the molecular weight of the resin. These results are discussed in the context of recent theories of the glass transition.     

Simulation of the glass transition and physical ageing

A kinetic model simulating the glass transition and enthalpic relaxation in poly(3-hydroxybutyrate) is introduced. The model is based on the concept that enthalpic relaxation or physical ageing is a continuation of the glass forming process and uses the KWW function to describe the glass formation process and the subsequent ageing of the glass. Non-linearity is introduced by incorporating a dependence of the relaxation time on the fictive temperature. The effects of non-linearity on the distribution of relaxation times and the physical ageing process are investigated together with the development of the endothermic ageing peak at the glass transition with increasing extents of ageing.     

玻璃化液体中构型熵与展宽弛豫函数关系的研究

The relationship between the transport properties and thermodynamic properties in glass forming liquids was investigated. The configurational entropy of Adam-Gibbs theory on cooperatively rearranging regions and the theoretic function derived from extremal value model were used to propose a brief that non-exponential stretched exponent in KWW form relaxation function is equal to the relative configurational entropy of cooperatively rearranging region in liquids, and is inversely proportional to the critical number of molecules occurring configurational transformation in a cooperatively rearranging region. Therefore, the new physical significance on glassy configuration is imposed on the stretched exponent, and theoretical developments and empirical correlations between the structural relaxation and configurational entropy are established. Further, an improved expression of β(T) was proposed to eliminate the deviation of the fit by using Vogel-Fulcher-Tammann equation from viscosity data at higher temperatures, which conforms well over 200 K temperature range. The improvement on β(T) is correspondent to the improvement on the difference in thermal capacities between isobaric and isochoric processes.     

不同结晶度的乙二醇及其水溶液玻璃化转变与焓松弛

为了考察晶体成分对无定形成分玻璃化转变和结构松弛行为的影响,利用差示扫描量热法(DSC),结合低温显微技术,研究了乙二醇(EG)及其50％水溶液在不同结晶度时的玻璃化转变和焓松弛行为.采用等温结晶方法控制骤冷的部分结晶玻璃体中的晶体份额.DSC结果表明,对于部分结晶的EG,只有单一的玻璃化转变过程,而对于50％EG,当结晶度不同时,不同程度地表现出两次玻璃化转变（无定形相Ⅰ和无定形相Ⅱ）.相Ⅰ的玻璃化转变温度和完全无定形态的含水EG的玻璃化转变温度相一致;相Ⅱ的玻璃化转变温度要比此温度约高6 ℃.低温显微观察结果印证了DSC实验结果.DSC等温退火的实验和KWW(Kohlrausch-Williams-Watts)衰变函数分析结果表明,EG无定形和50％EG中的两种无定形有不同的焓松弛行为.