炭黑填充聚苯乙烯熔体流变行为

研究了炭黑(CB)填充聚苯乙烯(PS)熔体的稳态和动态流变行为. CB/PS复合体系在CB体积分数φ=0.06时发生逾渗转变. 结果表明, 低应变区熔体模量降低主要归因于粒子-粒子及粒子-高分子间作用力的破坏, 高应变下模量的急剧下降则主要与高分子链间解缠结有关. 采用“两相”模型拟合线性动态流变行为, 发现应变放大因子A_f(φ)、填充相模量及松弛指数与温度有关. A_f(φ)~φ关系符合Guth方程和扩散控制的粒子簇聚集模型. “粒子相”形状参数与聚集体分维度均随温度升高而有所降低, 说明CB粒子聚集体因团聚而趋于各向同性, 应变放大效应减弱. “粒子相”特征模量G'_f1(φ)和G"_f0(φ)与φ关系满足标度律. 当φ > 0.06时, G'_f1(φ)和G"_f0(φ)及其标度指数均随温度升高而明显降低, 其G'_f1(φ)变化幅度略大于G"_f0(φ), 说明“粒子相”弹性与黏性组分具有不同的温度依赖性. 随着温度升高, 扩散控制的CB粒子团聚过程加快, 应变放大效应减弱.     

SiO2/PEG分散体系动态剪切流变行为

在动态应变条件下, SiO2/PEG200(聚乙二醇, 平均分子量为200)分散体系出现了剪切增稠现象. 剪切流变实验表明, 在两种情况下都出现了剪切增稠: 一种是在不同的恒定频率下应变扫描, 在临界应力γc出现的剪切增稠; 另一种是恒定的应变(γ0=500%)条件下频率扫描, 在临界频率棕c抑10 rad·s-1出现的剪切增稠. 在不同的恒定频率应变扫描条件下, 实验研究了储能模量(G’)和耗能模量(G’’)与应变的关系, 同时初步探讨了应变与不同恒定频率的函数关系. 在线性粘弹性区域内, G’和G’’满足G’∝ω0.57和G’’∝ω0.7指数关系. 在恒定的应变条件下, 发现模量和复数粘度与扫描频率具有强烈的依赖关系, 这些现象可以定性地通过“粒子簇”理论来解释.“粒子簇”理论认为这种剪切增稠的发生是由于形成了亚稳定、流动所导致的“粒子簇”, 使得粘度上升.     

多壁碳纳米管填充聚苯乙烯熔体的恒温依时性动态模量逾渗行为

在恒温(170～190℃)热处理过程中,多壁碳纳米管(MWCNTs)填充聚苯乙烯(PS)熔体发生动态模量逾渗(DMP)行为,且该行为服从时-温叠加(TTS)原理.MWCNTs体积分数(φ)低于逾渗阈值(φc)时,填充熔体在恒温热处理过程中保持类液行为,热处理对MWCNTs分散状态无显著影响,动态储能模量(G')与动态损耗模量(G″)活化能(EG'与EG″)分别高于、低于PS黏流活化能(Eω),而与PS熔体恒频动态模量活化能相一致;φ>φc时,热处理促成MWCNTs进一步团聚,填充熔体在热处理过程中发生类液-类固转变,EG'与EG″均低于Eω,而动态逾渗时间活化能(Et'与Et″)显著高于Eω且随φ增高而增大.在逾渗转变区,EG'与EG″发生不连续变化.PS/MWCNTs复合体系的恒温依时DMP行为与MWCNTs聚集所导致的三维弹性网络的形成密切相关,PS大分子终端松弛不是决定DMP的关键因素.     

SSBR/SiO_2混炼胶的动态黏弹行为

研究了白炭黑(SiO2)填充溶液聚合丁苯橡胶(SSBR)的动态流变行为,考察了时间-浓度叠加(time-concentration superposition,TCS)原理在粒子填充橡胶中的应用,获得以未填充SSBR为基准的流变叠加曲线.流变叠加曲线在低频下呈现模量平台,复数黏度呈现剪切变稀行为,而损耗因子tanδ在特定频率下出现峰值.基于刚性粒子所导致的应变放大效应以及SiO2粒子间SSBR分子的受限运动,探讨了TCS模量平移因子AG与频率平移因子Aω随SiO2体积分数φ的变化.AG与Aω均为φ的标度函数,但AG～φ关系不符合粒子聚集体团聚(cluster-cluster aggregation,CCA)模型.讨论了偶联剂3-辛酰基硫代-1-丙基三乙氧基硅烷(NXT)对动态流变行为的影响.NXT不影响性叠加曲线的低频平台模量与剪切变稀幂律指数.然而,与不含偶联剂的混炼胶相比,NXT造成SSBR特征弛豫时间缩短,稠度与A增大.     

加工工艺对气相生长碳纤维填充聚苯乙烯复合体系导电逾渗与动态流变特性的影响

研究了加工工艺对气相生长碳纤维(VGCF)填充聚苯乙烯(PS)复合体系导电逾渗与动态流变特性的影响.结果表明,低转速、短时间混合有利于VGCF形成较为完善的逾渗网络结构,其复合体系逾渗阈值低、导电性能好.使用作者提出的两相模型描述VGCF/PS复合体系的流变特性,发现低转速、短时间(30 r/min、5 min)混合条...     

泥鳅体表黏液的流变行为

研究了无鳞鱼———泥鳅的体表黏液流变行为,发现黏液的稳态流动存在着3个不同区域:第一区域内,黏度随剪切速率(γ)变化不显著,呈现牛顿流动行为;第二区域内,随γ增大,黏度下降,呈现非牛顿行为;第三区域内,随γ继续增大,黏度又基本保持不变.黏液表观黏度(ηa)与γ的关系可用Carreau模型很好地拟合,其增比黏度(ηsp)与浓度(c)的关系为ηsp∝c1.5,表明黏液处于亚浓缠结区域.在测试频率(ω)范围内,黏液的动态储能模量(G′)大于动态损耗模量(G″),表明与黏性相比较,弹性占优,且G′及G″随ω变化不显著.存在一临界温度(35℃),当低于35℃时,黏液黏度随温度变化不显著,当高于35℃时,黏液变性,表现出不同的流变行为.     

HDPE/石墨复合体系动态粘弹行为与Mooney方程改进

由于小应变条件下,动态流变行为的测定不会对材料本身的结构造成影响或破坏,动态流变研究被认为是表征填充类聚合物体系填料颗粒的分散状态的有效方法[1～3].众所周知,窄分子量分布的均相聚合物体系在低频率(ω)区域的粘弹行为满足线性粘弹关系,而填充类聚合物基复合材料的流变行为表现出特殊的粘弹特征[4～8],即在低ω区域显示出非线性粘弹行为的特殊响应.特别是所谓的"第二平台(second plateau)"现象,被认为与体系形态结构密切相关[9].     

硅烷偶联剂对SSBR/SiO_2混炼胶体系动态流变行为的影响

研究了高填充白炭黑(SiO2)补强溶液聚合丁苯橡胶(SSBR)混炼胶体系的动态流变特性,分别考察了在2个混炼温度(120℃、160℃)下添加3种不同偶联剂(TESPT、TESPD、NXT)对其体系中SiO2粒子表面改性的效果.结果表明,在较低混炼温度下添加偶联剂,不利于SiO2粒子表面改性.在较高混炼温度下,偶联剂TESPT、PESPD、NXT均对SiO2粒子表面有改性效果,但同时引起混炼胶不同程度的焦烧,其中以TESPT最明显.随SiO2粒子表面改性程度的提高,出现“Payne效应”的临界应变(γc)值以及低频率(ω)区域lgG′-lgω曲线的斜率值均增大,反映出偶联剂对SiO2与SSBR相互作用的促进以及SiO2粒子分散的改善.     

抗冲聚丙烯共聚物熔体结构演化的动态流变学表征

用动态流变学方法研究了抗冲聚丙烯共聚物(IPC)熔体的流变行为.通过探讨温度、抗氧剂、氧气的存在对其熔体动态粘弹响应的影响,对IPC熔体结构的演化过程进行了描述.随温度的升高,IPC熔体的动态粘弹响应明显改变,低频率(ω)区域动态储能模量(G′)与ω的对数关系lgG′-lgω呈现平台特征;加入复合抗氧剂B215或在N2气氛下,在一定的时间范围内,IPC的特征粘弹行为完全消失,呈现均相体系的流变响应特征.低ω区域粘弹函数对IPC的结构变化存在敏感响应.通过改变温度、添加抗氧剂以及N2保护,获得了IPC熔体因降解与交联反应所引起的结构改变的信息.     

电响应聚合物薄膜的表面图案化

研究了炭黑(CB)和石墨(GP)填充高密度聚乙烯(HDPE)复合体系的动态流变行为.发现高填料含量时出现似固体行为,并认为它归因于无机粒子网络逾渗结构的形成.在相同聚合物基体条件下,粒子种类和粒子几何参数(粒子形状、大小、粒径分布)对低频区域流变行为、流变参数的逾渗行为和逾渗阈值(φc)有决定性影响,且种类的影响相比于粒子几何参数更为显著.此外,高表面活性及高比表面积(大径厚比、小尺寸)粒子填充体系具有较低的φc.     

多壁碳纳米管填充聚苯乙烯复合体系的动态流变特性

应用两相模型探讨多壁碳纳米管(MWCNTs)填充聚苯乙烯(PS)复合体系的动态流变特性.结果表明,体系线性黏弹行为与PS本体的应变放大效应及MWCNTs填料相的弛豫密切相关.在不同温度下,应变放大因子(Af)随MWCNTs体积分数(φ)的变化规律符合扩散控制的粒子串聚集(CCA)模型.φ＜0.020时,MWCNTs分散...     

Temperature-induced gelation in dilute nanofluids

We report a temperature-induced gelation in dilute nanofluids containing surfactant capped iron oxide and alumina particles of average diameter ~10 nm. We observe a dramatic enhancement in the elastic modulus, viscous modulus, and viscosity, by 3-6 orders of magnitude for a volume fraction (φ) less than 0.035, above a critical shear rate ( ?γ(c)) and temperature (T(c)). The T(c) follows a weak power law scaling with φ as T(c) ~ φ(β), where the scaling exponent β is found to be -0.24. The observed gel-like transition at elevated temperature is attributed to strong van der Waals attractions on the kT energy scale due to poor solvent conditions, which is reminiscent of the phase behavior reported in polymer-coated colloids.     

Synthesis and Properties of Novel Hydrogels from Cross-linked Starch Phosphates

Summary: Starch based stable hydrogels providing high swelling and water storing capacity are not only of certain interest for the cosmetics and hygiene industry but also have the potential to become an effective tool in combating desertification and supporting cultivation in many regions of the world. It has been found that strong water adsorbing covalent networks with free swelling capacity (FSC) of up to 190 g water/g hydrogel can be obtained by cross-linking low-substituted mono-starch phosphates (MSP) in a semi-dry process with di- and tricarboxylic acids such as succinic acid (SA), adipic acid (AA) or citric acid (CA). The linear behaviour over a wide frequency range of the rheological parameters G′ and G″ which were determined by using a shearing disc viscosimeter clearly reveal that the cross-linked starch phosphates are stable hydrogels having stronger elastic than viscous properties.     

Nonlinear rheological behavior of silica filled solution‐polymerized styrene butadiene rubber

The reinforcement and nonlinear viscoelastic behavior have been investigated for silica (SiO₂) filled solution‐polymerized styrene butadiene rubber (SSBR). Experimental results reveal that the nonlinear viscoelastic behavior of the filled rubber is similar to that of unfilled SSBR, which is inconsistent with the general concept that this characteristic comes from the breakdown and reformation of the filler network. It is interesting that the curves of either dynamic storage modulus (G′) or loss tangent (tan δ) versus strain amplitude (γ) for the filled rubber can be superposed, respectively, on those for the unfilled one, suggesting that the primary mechanism for the Payne effect is mainly involved in the nature of the entanglement network in rubbery matrix. It is believed there exists a cooperation between the breakdown and reformation of the filler network and the molecular disentanglement, resulting in enhancing the Payne effect and improving the mechanical hysteresis at high strain amplitudes. Moreover, the vertical and the horizontal shift factors for constructing the master curves could be well understood on the basis of the reinforcement factor f(φ) and the strain amplification factor A(φ), respectively. The surface modification of SiO₂ causes a decrease in f(φ), which is ascribed to weakeness of the filler–filler interaction and improvement of the filler dispersion. However, the surface nature of SiO₂ hardly affects A(φ). © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2594‐2602, 2007     

不同分子量可德胶水悬浮液的粘弹性研究

采用动态粘弹性测量研究了不同分子量的生物大分子可德胶 (Curdlan)水悬浮液 (ASC)的流变学特性 .室温下观察到ASC具有弹性 (Solid like)行为 ,储能模量G′在测量范围内轻微依赖频率 ,而损耗模量G″和损耗角正切tanδ存在最小值 .ASC粘弹性随可德胶分子量和浓度的增加而增强 .ASC的流动特性符合Herschel Bulkley模型 ;其弹性行为可以通过渗流理论的标度弹性模型来描述 .网络结构是由于可德胶颗粒聚集或絮凝而形成的 ,当可德胶含量超过临界浓度cs=0 3 %时 ,弹性模量G′与可德胶浓度存在标度关系G′=Goεt,其中标度指数t=2 5 4.     

Viscoelastic properties of cross-linked polyvinyl alcohol and surface-oxidized cellulose whisker hydrogels

Reinforcement of polyvinyl alcohol (PVA) hydrogels was achieved by direct chemical cross-linking of surface modified microcrystalline cellulose (MCC) whiskers with PVA. In order to produce hydrogels, the MCC whiskers were first obtained by TEMPO-mediated oxidation of the cellulose substrate and ultrasonication followed by direct cross-linking to PVA (Mw 98,000) via forming acetal bonds and freeze–thawing. The viscoelastic properties of the produced hydrogels were clearly improved following the chemical cross-linking, featuring values for viscous and elastic moduli G′ and G″ on the order of 10 kPa, which is particularly interesting for biomedical orthopedic applications.     

C12NBr对黄原胶/Cr(Ⅲ)凝胶体系粘弹性的影响

以三价铬离子（Cr3＋,Cr(Ⅲ)）为交联剂制备的黄原酸(XC)凝胶在油田开发过程中具有许多用途,应用RS 75型流变仪测定了含有和不含有阳离子表面活性剂C12NBr (十二烷基-氧丙基-β-羟基-三甲基溴化铵)时凝胶体系粘弹性的变化规律.结果表明,XC凝胶体系不符合理想的线性粘弹性模型,储能模量（G′）和耗能模量（G″）在切力较低时变化甚微,切力较高时两者皆降低,但降低的幅度不同,因而G′～τ（应力）和G″～τ曲线出现交点,此交点随C12NBr浓度增大而降低.结合等温线的研究表明,C12NBr能结合到XC分子上,破坏凝胶的网络结构.然而,在一定条件下其复合粘度（η*）随频率和切力的变化出现最低值现象的机理还有待进一步探讨.     

Etude rheologique de gels mixtes de poly(alcool vinylique) et d'alginate de sodium

Snake-cage hydrogels were prepared by the association of poly(vinyl alcohol) (PVA) and sodium alginate. The aim of this work is to study the viscoelastic properties of PVA networks having different molecular weights and trapping alginates of various mannuronate/guluronate ratios, molecular weights and aqueous concentration. The elastic and viscous moduli, G′ and G″, were found to depend on alginate concentration. With the sodium alginate (mannuronate/guluronate =1.78, M̄w=380 000), the elasticity was observed to be independent of the PVA molecular weight in the 7.5% to 10% (w/w) concentration range. Hydrogels elasticity was found to be sodium alginate nature-dependent only in the case of PVA with M̄w =22 000. Moreover, it seems that the viscoelastic parameters G′ and G″ become increasingly insensitive to the nature of sodium alginate as the molecular weight of PVA increases.