多组分聚合物的动态流变特性

用动态流变学方法来研究聚合物的粘弹性具有独特的优点,它是研究多组分体系的形态和结构的一种有效方法。文中介绍了动态流变学方法测试高聚物的粘弹性的特点和理论,根据动态流变学理论分析高分子共混和填充体系动态流变学行为,并分析相分离、相形态、分子量分布等因素对动态粘弹性能的影响。     

粒子填充聚合物体系的特征粘弹行为

以线性粘弹理论为依据，介绍粒子填充聚合物体系动态流变行为，探讨影响填充聚合物体系粘弹性的主要因素，并对粒子填充聚合物体系粘弹机制的若干进展进行了简要概述。     

PPC/PBS共混体系的粘弹特性

用熔融共混法制备了聚碳酸亚丙酯(PPC)/聚丁二酸丁二醇酯(PBS)共混材料,并采用流变学方法对所制备的共混体系的粘弹特性进行了深入研究。结果表明,PPC/PBS为典型的热力学不相容体系,PBS的加入提高了PPC的加工性能;当PBS的质量分数约为40%~50%时,体系发生相反转,这与Paul模型对相反转点预测的结果一致;在相分离区,动态模量偏离了经典的低频末端标度规则,Han图表现出不同于均相体系的特征,引起时温叠加原理失效;与Gramspacher-Meissner模型相比,Palierne模型可以较好地描述PPC/PBS体系的线性粘弹行为。     

聚氯乙烯／增韧剂共混体系动态力学性能的研究

使用日本ＤＤＶ－Ⅲ－ＥＡ型动态粘弹仪研究了ＰＶＣ与３种增韧剂分别共混后的动态力学性能，结果表明，增韧剂的化学结构对该共混体系的动态力学性能影响显著。在这３种共混物中，动态力学性能随共混组成变化的规律不同，但随共混温度而变化的规律相同。     

支化程度和支链长度对支化聚苯乙烯粘弹行为的影响

将星形支化聚苯乙烯与线型聚苯乙烯共混组成支化体系,使用旋转流变仪测定样品的动态粘弹温度谱和频率谱,研究了支化结构对支化聚苯乙烯粘弹性能的影响。结果表明,支化程度对支化PS粘弹行为的影响与支链长度有关。长支链体系(支链的珨Mw,branch大于2 Me)中支链对链缠结具有促进作用,随支化程度增加,受相对分子质量和缠结的共同影响,支化PS在玻璃态与橡胶态的储能模量(G′)升高,玻璃化转变温度(Tg)、粘流转变温度(Tf)和主链特征松弛时间(τe)明显上升和延长,末端弹性效应增强,并在高频下观察到支链解缠结松弛。短支链体系(支链的珨Mw,branch小于2 Me)的支链对链缠结有抑制作用,随支化程度增加,支化PS的Tg,Tf和τe升速较慢,末端弹性效应表现不明显,高频下未观察到支链松弛。     

纤维增强聚合物复合材料的三相动态粘弹模型及其界面结构参数

本文以复合材料界面作为中间相(界面相),借助Takayanagi的两相共混模型及Ziege的修正公式,导出了单向纤维增强聚合物复合材料的三相动态粘弹共混模型,得到了界面层的几何结构混合参数(r_i、V_i、λ_L及中间参数B)及界面相的各个动态粘弹性参数.这些参数可以根据复合材料的动态粘弹性实验结果求得,利用上述导出的模型,对玻璃纤维单向增强不饱和聚酯的动态粘弹性进行了试验,结果表明,随着温度的变化,界面相的厚度r_i、体积分数V_i及动态粘弹参数也会发生一定的变化,存在着界面相与基体相之间的相互转变.      

聚合物基导电复合材料的粘弹性电阻响应

用自制的微机控制同步测量装置考察了聚合物基导电复合材料电阻的长时响应及动态粘弹响应。研究结果表明,导电复合材料的电阻蠕变和电阻松弛的根源在于大分子的力学松弛,其方向与蠕变及松弛实验开始前的压阻方向有关。对电阻正温度系数(PTC)行为的分析显示,模量的改变可能是PTC行为发生的内在机制;而动态剪切对导电粒子运动的协助作用及高聚物基体模量降低导致的CB接触几率增加均可能是动态条件PTC行为改变的原因。     

振动力场作用下聚合物熔体粘弹行为的研究

连续介质力学、高分子微观结构动力学和流变测量学三者相结合，分析了小振幅振荡振动、大振幅振荡振动、电磁动态振动、稳定剪切流动上平行或垂直叠加振动等四个不同的振动引入方式下聚合物熔体粘弹行为的研究现状。重点介绍了作者们在不依赖现有任何本构关系条件下建立的动态成型过程中聚合物熔体非线性粘弹行为的表征理论、以及电磁动态塑化挤出条件下聚合物熔体输送和挤出机理的近似解释理论。     

PVC/CPE共混体系相容性-形态-冲击强度关系的研究

本文使用日本产DDV-Ⅲ-EA型动态粘弹仪、扫描电子显微镜(SEM)及其它辅助设备,对国产PVC/CPE其混体系进行了讨论。结果表明,PVC/CPE属界面相容(compatible)共混体系,该体系的界面相容性与其动态力学谱图“E”曲线上各组分之T_g峰位无关,只与二组分之次级转变峰及二组分之松弛峰是否有一定互融性有关。共混组成、温度及时间是影响体系相容性、形态及冲击强度的重要因素。共混条件一定时,体系的相容性、冲击强度随CPE含量增加有一最佳值,此时形态结构对增韧最有利,大于或小于该含量都不能得到理想的增韧效果。共混组成一定时,随共混条件不同,体系的上述性能也随之改变,也存在一最佳值。所以,适当选择共混条件厦改性剂用量尤为重要。     

PVA／P（VA—VP）共混物的动态力学性能

用粘弹谱法(DVE)研究了醋酸乙烯酯和乙烯基吡咯烷酮共聚物的水解物P(VA-VP)和聚乙烯醇(PVA)共混体系的动态力学行为。共混物的阻尼松弛谱(tgδ)表明了共混体系的相容性随着组成比的不同而明显不同,一些组成比的共混物不仅存在晶相和非晶相的聚态结构,而且在非晶相态里随着组成比的不同还存在着微观结构不均匀性和相容性的差异。组成比(W_(PVA))为40～60％的共混物其复合模量和tgδ谱表明共混物中PVA的晶相是均匀分散在共容的非晶介质中,因而在室温至约80℃范围内能形成强度比纯PVA更好的有实用意义的功能PVA合金。 选择两种不同组成比的共混物通过改变升温速率和作用力频率的试验表明,随着升温速率的下降,非晶部分的相容性增大而晶相部分的结晶度增加;作用力频率的下降导致结晶度提高和T_8真升高。     

纳米纤维素对两性蠕虫胶束线性黏弹性的影响

对两性蠕虫胶束（Z-WLM）溶液添加不同类型纳米纤维素（NCs）后的耐温性能进行了研究,并通过线性流变学方法分析了不同浓度的NCs对Z-WLM的动态黏弹性、触变性、蠕变性等流变行为的影响。研究结果表明,质量分数为4wt%的芥酸酰胺丙基二甲基甜菜碱表面活性剂溶液可形成蠕虫胶束（WLM）结构,具有剪切稀释性、黏弹性、蠕变性及良好的触变回复性等特性。与其它类型NCs相比,长径比大、羧基含量高的NCs对WLM溶液拥有更好的增黏作用,同时可增加体系的松弛时间、弹性模量,延长其剪切黏度及动态模量触变回复时间,改善其蠕变回复性和耐温性,适用于70~100℃的中高温油藏增产作业使用。随着NCs添加量的增加,复合体系的黏弹性和蠕变回复性增强,触变回复性减弱。      

Numerical analysis of the creep of the contact and recovery of the imprint on amorphous polymer surfaces

This article attempts to analyze the viscoelastic behavior of an amorphous polymer during a microindentation test. The viscoelastic behavior of an amorphous polymer (poly(methyl methacrylate), PMMA) is derived from different relaxation tests performed under different applied true strains. A generalized Maxwell model is then used to identify the mechanical parameters of the viscoelastic behavior. The numerical results display good correlation with experiments during the creep phase. The uniaxial relaxation test used to identify the viscoelastic behavior is chosen in relation to the experimental conditions of indentation. The results obtained for the recovery phase allow a first analysis of the strain and von Mises equivalent stress fields during indentation test. The recovery of the imprint left on the surface seems to depend on the location of the strain maxima. If a strain level of 10 % or more reaches the surface of the deformed volume, a permanent imprint is obtained. Otherwise the residual imprint may be considered to be completely healed even if the subsurface has partially yielded during the loading phase or creep time.     

Continuous relaxation and retardation spectrum method for viscoelastic characterization of asphalt concrete

This paper presents a simple and practical approach to obtain the continuous relaxation and retardation spectra of asphalt concrete directly from the complex (dynamic) modulus test data. The spectra thus obtained are continuous functions of relaxation and retardation time. The major advantage of this method is that the continuous form is directly obtained from the master curves which are readily available from the standard characterization tests of linearly viscoelastic behavior of asphalt concrete. The continuous spectrum method offers efficient alternative to the numerical computation of discrete spectra and can be easily used for modeling viscoelastic behavior. In this research, asphalt concrete specimens have been tested for linearly viscoelastic characterization. The linearly viscoelastic test data have been used to develop storage modulus and storage compliance master curves. The continuous spectra are obtained from the fitted sigmoid function of the master curves via the inverse integral transform. The continuous spectra are shown to be the limiting case of the discrete distributions. The continuous spectra and the time-domain viscoelastic functions (relaxation modulus and creep compliance) computed from the spectra matched very well with the approximate solutions. It is observed that the shape of the spectra is dependent on the master curve parameters. The continuous spectra thus obtained can easily be implemented in material mix design process. Prony-series coefficients can be easily obtained from the continuous spectra and used in numerical analysis such as finite element analysis.     

Universal linear viscoelastic approximation property of fractional viscoelastic models with application to asphalt concrete

The paper presents a comprehensive linear viscoelastic characterization of asphalt concrete using fractional viscoelastic models. For this purpose, it is shown that fractional viscoelastic models are universal approximators of relaxation and retardation spectra. This essentially means that any spectrum can be mathematically represented by fractional viscoelastic models. Characterization of asphalt concrete is performed by constructing the dynamic modulus master curve and determining the parameters of the generalized fractional Maxwell model (GFMM). This procedure is similar to the widely used one of determining the master curve of asphalt concrete using a statistical function such as the sigmoidal model. However, from the GFMM, the relaxation modulus, creep compliance, continuous relaxation spectrum, and Prony series parameters can be determined analytically. A further advantage of the GFMM is that unlike the sigmoidal model, which only gives a representation of either the dynamic modulus or the storage modulus, the GFMM gives a representation of both the storage modulus and loss modulus (and therefore also the dynamic modulus and phase angle). The procedure was successfully applied to ten different mixes used in the State of Virginia.     

A hyper-viscoelastic constitutive model for polyurea

This letter presents a new constitutive model for polyurea by superposing the hyperelastic and viscoelastic behaviors of polyurea. The Ogden model is used for the hyperelastic part and its parameters are determined from curve fitting of quasi-static test data. A nonlinear viscoelastic model is employed for describing the viscoelastic behavior and its relaxation time is obtained based on the test data of shear relaxation modulus. A special form of Zapas kernel for the damping function is found to be very effective to capture the viscoelastic behavior of polyurea subjected to wide ranges of strain rate. Both the versatility and accuracy of the model are examined via virtual testing.     

沥青混合料黏弹性主曲线模拟及换算

基于时间-温度等效原理将不同温度下沥青混合料的储存模量和蠕变柔量进行平移形成主曲线,采用广义Maxwell和Kelvin模型分别模拟沥青混合料的松弛和蠕变特性,利用Prony级数表达式和Laplace变换实现黏弹性主曲线间的相互换算,并将换算结果与试验结果进行了比较。结果表明,广义Maxwell和Kelvin模型可以较好地模拟沥青混合料黏弹性主曲线,储存模量和蠕变柔量主曲线相互换算结果与试验结果规律基本一致,松弛模量实际结果应介于由储存模量和蠕变柔量换算的松弛模量主曲线之间,这可为沥青混合料黏弹性力学研究及黏弹性参数的获取提供有益参考。     

Nonlinear thermomechanical dynamic buckling analysis of imperfect viscoelastic composite/sandwich shells by a double-superposition global–local theory and various constitutive models

Almost no dynamic buckling analysis has been performed so far for the sandwich/multilayer viscoelastic shells. Even the vibration analyses of the mentioned shells have been restricted to the harmonic loads ignoring the transverse stresses and their continuity at the mutual interfaces of the layers, and the transverse flexibility of the shell. In the present paper, a high-order double-superposition global–local theory inherently suitable for nonlinear analyses is proposed and employed for nonlinear dynamic buckling and postbuckling analyses of imperfect viscoelastic composite/sandwich cylindrical shells subjected to thermomechanical loads. Depending on the nature of the applied loads, both complex modulus and hierarchical constitutive models are used for the viscoelastic materials. Results reveal that as the time duration of the suddenly applied loads decreases beyond the first natural period of the shell, the dynamic buckling load becomes much higher than the static buckling load, especially for the rectangular load–time histories. Furthermore, the relaxation behavior of the viscoelastic material may decrease the dynamic buckling load.     

Viscoelasticity and relaxation characteristics of polystyrene/clay nanocomposite

Polymer nanocomposites based on an organophilically modified montmorillonite (OMMT) and polystyrene (PS) are prepared via a solvent casting method using chloroform as a cosolvent to examine their dynamic viscoelastic and relaxation properties, in which the increased basal spacings of the OMMT determined by X-ray diffraction indicated the intercalation of PS chains into OMMT interlayer. From the measured viscoelastic properties originated from the nanocomposite interaction between polymer and OMMT, we were able to determine the characteristic behavior of PS/OMMT nanocomposites. Storage and loss moduli are found to give the transition from liquid-like to solid-like behavior as the clay content increases, especially in the low frequency region. Stress relaxation behavior was also enhanced by showing more solid-like characteristics with increasing OMMT.