EPDM受热氧化与动态流变行为

采用动态流变学方法研究了三元乙丙橡胶(EPDM)高温氧化与动态粘弹响应之间的关系.在熔体状态下,EPDM的动态粘弹行为随温度升高而改变,呈现出非均相结构的流变响应特征;加入复合抗氧剂后,EPDM在一定的时间范围内,呈现均相体系的流变响应特征.这些结果表明,流变响应特征的改变与受热导致EPDM熔体氧化进而引起结构的改变密切相关.低频区域粘弹函数对EPDM结构变化具有敏感响应,2 0 0～2 2 0℃可明显观察到受热氧化导致EPDM结构的生成.     

Linear Viscoelastic Behavior of Multiphase Dispersions

The linear viscoelastic behavior of polymer-thickened oil-in-water emulsions, polymer-thickened solids-in-liquid suspensions, and their blends is investigated using a controlled-stress rheometer. The emulsions exhibit a predominantly viscous behaviour at low values of oil concentration in that the loss modulus (G") exceeds the storage modulus (G') over most of the frequency range. At high values of oil concentration, the emulsions exhibit a predominantly elastic behavior. The ratio of storage modulus to loss modulus (G'/G") increases with the increase in oil concentration. Emulsions follow the theoretical model of J. F. Palierne (1990, Rheol. Acta 29, 204) only at low values of oil volume fraction (/=G' over most of the frequency range. The ratio G'/G" varies only slightly with the increase in solids volume fraction. The Palierne model describes the linear viscoelastic properties of suspensions accurately only at low values of solids volume fraction. At high values of solids concentration, the Parlierne model underpredicts the linear viscoelastic properties of suspensions and the deviation increases with the increase in solids concentration. The blends of emulsions and suspensions exhibit strong synergistic effects at low to moderate values of frequencies; the plots of blend modulus versus emulsion content exhibit a minimum. However, at high values of frequency, the blend modulus generally falls between the moduli of pure suspension and pure emulsion. The high-frequency modulus data of blends of emulsions and suspensions are successfully correlated in terms of the modulus ratio versus volume fraction of solids, where modulus ratio is defined as the ratio of blend modulus to pure emulsion modulus at the same frequency. Copyright 2000 Academic Press.     

Mesoscopic dynamics of inhomogeneous polymers based on variable cell shape dynamic self-consistent field theory

In this paper, we combine variable cell shape method with dynamic self-consistent field theory and extend to study structure and dynamics under shear for triblock copolymer melts. Due to shear, the calculation cell shape is variable and no longer orthogonal. Pseudospectral method is employed to solve the diffusion equation for chain propagator on the nonorthogonal coordinate and the shear periodical condition can be easily designed in terms of the variable cell shape method. By using this strategy, the shear induced morphology evolution is investigated for topologically complex polymeric systems such as linear and star triblock copolymers; the morphology of linear ABC triblock copolymers is more shear sensitive than that of star triblocks. In particular, once the chain propagator is obtained, the microscopic elastic stress and spatial stress distribution can be derived and thus the dynamic mechanical property can be calculated under shear. By imitating the dynamic storage modulus G' corresponding to any given morphology in the oscillatory shear measurements, we explore the relationship between the morphology and the storage modulus G' and extend to study the mechanism of phase separation dynamics as well as order-disorder transition (ODT) for linear and star triblock copolymers. The results show that the chain architecture can be easily distinguished by investigating the ODT, though the systems such as AB symmetric diblock and ABA triblock copolymers by coupling AB precursors almost exhibit similar microstructures. In addition, the storage modulus G' and loss modulus G" can be simultaneously determined in frequency sweeps of oscillatory shear measurements and the dependence of the moduli on phase separated patterns and the chain topology is investigated. The simulation findings are in qualitatively agreement with the experimental results.     

Nonlinear viscoelasticity of sorbitan tristearate monolayers at liquid/gas interface

The interfacial rheology of sorbitan tristearate monolayers formed at the liquid/air interface reveal a distinct nonlinear viscoelastic behavior under oscillatory shear usually observed in many 3D metastable complex fluids with large structural relaxation times. At large strain amplitudes (gamma), the storage modulus (G') decreases monotonically whereas the loss modulus (G') exhibits a peak above a critical strain amplitude before it decreases at higher strain amplitudes. The power law decay exponents of G' and G' are in the ratio 2:1. The peak in G' is absent at high temperatures and low concentration of sorbitan tristearate. Strain-rate frequency sweep measurements on the monolayers do indicate a strain-rate dependence on the structural relaxation time. The present study on sorbitan tristearate monolayers clearly indicates that the nonlinear viscoelastic behavior in 2D Langmuir monolayers is more general and exhibits many of the features observed in 3D complex fluids.     

HDPE氧化交联与动态流变行为

研究了高密度聚乙烯(HDPE)熔体在200℃的动态流变行为,比较了空气、氮气及加入抗氧剂B215情况下体系动态粘弹行为的差异.研究表明,在空气环境中,HDPE在低频区域出现特征粘弹行为.随着测试前热处理时间的延长,动态储能模量(G')明显增加,在低频率(ω)区域lgG'～lgω关系呈现平台特征.同时损耗角tanδ变小并出现极大值.在氮气环境中,上述特征粘弹行为存在但不明显.在加入抗氧剂的条件下,特征粘弹行为完全消失.这些现象归因于高温下HDPE的氧化导致其发生交联.     

非离子表面活性剂液晶的线性粘弹性研究

用偏光显微镜测定了十二/十四烷基聚氧乙烯醚(C12～14EO7)/水二元体系相图的液晶区,用RS-75控制应力流变仪,在固定频率(f=0.0316Hz)时,对不同样品进行应力扫描。利用线性粘弹性区内流变参数G"与G'的比值thδ对相转变敏感的特点来确定相结构的转变,并将结果与2^HNMR结果相比较,两者吻合,这表明宏观测量手段能够反映微观相结构的变化规律。对于液晶实验结果采用弹簧-粘壶模型进行解释和讨论。     

聚乙烯交联过程结构演化的流变学研究

采用耐压等级分别为35kV及110kV的两种不同商业化可交联聚乙烯(XLPE)电缆料为研究模型,考察其化学交联过程中结构演化与线性黏弹响应的关系.研究结果表明,流变学方法可敏感表征较低温度、较长时间下XLPE交联过程的结构演化.随着交联温度的升高,体系预交联时间缩短,而黏弹特性的变化速率不变;交联导致体系弹性和黏性均增加,但弹性增加幅度远大于黏性增加幅度.比较两种样品交联过程的流变行为,发现随着交联反应的进行,两者的黏性增长速率基本一致,但35kV电缆料样品的弹性增长略大.采用低频率区域(频率末端区)的动态储能模量(G′),计算体系交联点之间的平均分子量(Mc),以表征样品的交联密度.同时用常规的溶胀平衡法研究了两种电缆料Mc与交联时间的依赖关系.     

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.     

Effect of microstructure uncertainty and testing frequency on storage and loss moduli of injection molded MWCNT reinforced polyamide 66 nanocomposites

The viscoelastic behavior of multiwall carbon nanotube (MWCNT) reinforced polyamide 66 (PA 66) was evaluated to investigate the effect of CNT content and loading frequency on dynamic moduli (i.e. storage modulus E′ and loss modulus E″) and damping factor tan$\delta$. PA 66/CNT disk samples with five different CNT contents ranging from 3 wt % to 15 wt % were manufactured by injection molding. Testing was performed over the frequency range of 0.1–100 Hz at room temperature. Dynamic mechanical analysis results show that the mechanical properties are highly functions of tested frequency and the improvement on loss and storage modulus of nanocomposites with the addition of CNT is highly dependent on tested frequencies. The variability in loss modulus is significantly higher than the variability in the storage modulus indicating the correlation of loss modulus with uncertainties present in nanocomposite microstructure while storage modulus is essentially independent of microstructure for a given reinforcement content.     

STUDY ON PHASE-SEPARATION OF PMMA/SAN BLENDS INDUCED BY GLASS BEADS THROUGH DYNAMIC RHEOLOGICAL MEASUREMENTS

Based on the premise that the addition of glass beads （GB） could hardly influence the linear viscoelasticity in low frequency （ω） region for homogeneous polymer systems, the dynamic rheological behaviors of unfilled and filled poly（methyl methyacrylate） （PMMA）/poly（styrene-co-acrylonitrile） （SAN） blends were studied in order to explore the effect of GB on the phase-separation of binary polymer matrix. Results show that GB has an induced effect on the phase-separation, which embodies that the phase-separation temperature （Ts） of PMMA/SAN blend filled with GB is lower than that of the unfilled system. The higher content of GB, the higher is the ＂secondary plateau＂ of ω in the terminal region of storage modulus （G＇） versus ω plot. The ＂secondary plateau＂ appearing in the terminal region is attributed to the phase-separation of PMMA/SAN blends and it becomes more fiat for filled polymer blends under the same conditions. However, it is suggested that this kind of ＂induced effect＂ is related to the GB content; the higher content of GB particles might enhance the interaction between the particles and polymer matrix. Moreover, it is found that the addition of GB also has an influence more or less on the morphology and domain size of polymer matrix. It is believed that the plot of dynamic viscosity （η＇） versus the loss viscosity （η＂） is sensitive to examine the effect induced by GB on the phase-separation of binary polymer matrix.     

MORPHOLOGY AND MECHANICAL PROPERTIES OF POLY(ETHYLENEOCTENE) COPOLYMERS OBTAINED BY DYNAMIC PACKING INJECTION MOLDING*

The morphology and mechanical properties of poly(ethylene-octene)copolymers(POE)obtained by dynamic packing injection molding were investigated by mechanical tests,differential scanning calorimetry(DSC),fourier transform infrared spectroscopy(FT-IR)and scanning electron microscopy(SEM).The mechanical tests found that only POE with low octene content and high molecular weight show apparent response for external shear field.Further investigation has been done by DSC,FT-IR,and SEM in order to make clear the reason of that phenomenon.Finally,the hypothetical mechanism of POE microstructure formation under shear field has been proposed.For POE with low octene content and high molecular weight,orientation degree and mechanical properties both increase substantially under shear field.For POE with low octene content and low molecular weight,orientation degree and crystallinity increase under shear field,but it is not dramatically benefit for the mechanical properties.For POE with high octene content and high molecular weight,the shear field has little effect on the morphology and mechanical properties.     

流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

New semi-interpenetrating network hydrogels: synthesis, characterization and properties

Amphiphilic hydrogels composed of aliphatic polyesters and poly(ethylene glycol) have potential applications in drug delivery, tissue engineering and other biomedical devices due to their advantageous biological properties, biocompatibility and biodegradability. However, they also exhibit some shortcomings in terms of their reactivity, swelling and mechanical properties. To address these limitations, new semi-interpenetrating network (semi-IPN) hydrogels based on poly(ethylene glycol)-co-poly(epsilon-caprolactone) (PEG-PCL) diacrylate macromer and hydroxypropyl guar gum (HPGG) were prepared by a low intensity ultraviolet (UV) light irradiation method, and characterized by FT-IR, DSC and WAXD analysis. Their properties were evaluated by investigating the swelling kinetics, dynamic mechanical rheology and the release behavior for bovine serum albumin (BSA). It was found that the introduction of the semi-IPN structure and HPGG decreased the crystallinity of PEG segments in the hydrogel, and improved the swelling and mechanical properties of the hydrogel, as well as lowered the release percentage of BSA from the hydrogel. Such hydrogel materials may have more advantages as a potentially interesting platform for the design of medical devices.The elastic modulus (G') and viscous modulus (G') as a function of frequency for various hydrogel samples.     

表面活性剂对氧化锰悬浮体系流变学振荡行为的影响

对介孔氧化锰的溶胶-凝胶法合成和用表面活性剂（脂肪醇聚氧乙烯醚, AEO_9)的模板合成过程中所得的悬浮体系的流变性质进行了对比研究。结果表明： 上述体系均具有触变性,且无论是否预剪切,其表观粘度均随时间作周期性振荡; 同时上述体系的储能模量G'和损耗模量G"亦具有周期性的振荡行为。但表面活性剂 AEO_9的引入使体系的触变性大为减弱,屈服值明显降低,凝胶结构强度减弱。同 时还发现引入AEO_9的模板合成过程中,不仅体系的表观粘度及G'大幅度下降,且 G'与G"的振荡周期显著增大,振幅亦明显减小。这说明体系中两亲分子与无机物存 在较强的相互作用,作者还对这些现象进行了讨论。     

Interfacial rheology of an ultrathin nanocrystalline film formed at the liquid/liquid interface

We report the interfacial properties of monolayers of Ag nanoparticles 10-50 nm in diameter formed at the toluene-water interface under steady as well as oscillatory shear. Strain amplitude sweep measurements carried out on the film reveal a shear thickening peak in the loss moduli (G") at large amplitudes followed by a power law decay of the storage (G') and loss moduli with exponents in the ratio 2:1. In the frequency sweep measurements at low frequencies, the storage modulus remains nearly independent of the angular frequency, whereas G" reveals a power law dependence with a negative slope, a behavior reminiscent of soft glassy systems. Under steady shear, a finite yield stress is observed in the limit of shear rate .gamma going to zero. However, for .gamma > 1 s-1, the shear stress increases gradually. In addition, a significant deviation from the Cox-Merz rule confirms that the monolayer of Ag nanoparticles at the toluene-water interface forms a soft two-dimensional colloidal glass.     

Synchrotron SAXS/WAXD and rheological studies of clay suspensions in silicone fluid

Suspensions of two commercial smectite clays, montmorillonite KSF and montmorillonite K10, in a low-viscosity silicone oil (Dow Corning 245 Fluid) were studied by simultaneous synchrotron small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) techniques and rheological measurements. In the 0.5% (w/v) KSF clay suspension and two K10 clay suspensions (0.5% and 1.0%), WAXD profiles below 2theta=10.0 degrees did not display any characteristic reflection peaks associated with the chosen montmorillonite clays, while corresponding SAXS profiles exhibited distinct scattering maxima, indicating that both clays were delaminated by the silicone oil. In spite of the large increase in viscosity, the clay suspensions exhibited no gel characteristics. Dynamic rheological experiments indicated that the clay/silicone oil suspensions exhibited the behavior of viscoelasticity, which could be influenced by the type and the concentration of the clay. For the K10 clay suspensions, the frequency-dependent loss modulus (G") was greater in magnitude than the storage modulus (G') in the concentration range from 0.5 to 12.0%. The increase in the clay concentration shifted the crossover point between G' and G" into the accessible frequency range, indicating that the system became more elastic. In contrast, the KSF clay suspension exhibited lower G' and G" values, indicating a weaker viscoelastic response. The larger viscoelasticity response in the K10 clay suspension may be due to the acid treatment generating a higher concentration of silanol groups on the clay surface.     

The Dynamic Viscoelasticity of Polyethylene Based Montmorillonite Intercalated Nanocomposites

The viscoelastic behavior of melts for two systems composed of intercalated nanocomposites based on low density polyethylene and 3 wt% loading of cetyltrimethylammonium bromide modified montmorillonite was studied. The results obtained through examining the dynamic storage module G‘ and dynamic loss module G“ values of the composite revealed that the dynamic viscoelastic properties of composite strongly depended on intercalation of polymer, and exhibited dramatically change with altering intercalation conditions. Only when modified montmorillonite content was about 3 wt%, the composite showed a trend of pseudo-solidlike at lower frequencies.     

Supramolecular hydrogels induced rapidly by inclusion complexation of poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) block copolymers with alpha-cyclodextrin in aqueous solutions

On the basis of the synthesis of water-soluble poly(epsilon-caprolactone)-poly(ethylene glycol)-poly(epsilon-caprolactone) (PCL-PEG-PCL) block copolymers, the supramolecular hydrogels were fabricated rapidly in aqueous solutions by their inclusion complexation with alpha-cyclodextrin. X-ray diffraction (XRD) analyses confirmed the supramolecular self-assemblies of alpha-cyclodextrin threaded onto amphiphilic PCL-PEG-PCL block copolymers. The resulting hydrogels display a high degree of elasticity, with the storage modulus (G') greater than the loss modulus (G') over the entire range of frequency. Moreover, their viscosity greatly diminished as they were sheared. By controlling the molecular weight of the PEG component in the block copolymers and the content of the block copolymer, their rheological properties could be modulated. Such hydrogel materials have the potential to be used as tissue engineered scaffolds, biosensors in the human body, and carriers for controlled drug delivery.     

Thermal gelation of cellulose in a NaOH/thiourea aqueous solution

Utilizing a novel solvent of cellulose, 6 wt % NaOH/5 wt % thiourea aqueous solution, for the first time, we prepared the thermally induced cellulose gel. We investigated the thermal gelation of cellulose solutions with rheometry and the structure of the gel with 13C NMR, wide-angle X-ray diffraction, environmental scanning electron microscopy, and atomic force microscopy. The cellulose solutions revealed an increase in both the storage modulus (G') and the loss modulus (G") with an increase in the temperature during gelation. The temperature at the turning point, where G' overrides G" because of the onset of gelation, decreased from 38.6 to 20.1 degrees C with an increase of cellulose concentration from 4 to 6 wt %. Given enough time, G' of all solutions can exceed G" at a certain temperature slightly lower than the gelation temperature, indicating that the occurrence of the gelation is also a function of time. Each of the assigned peaks of NMR of the cellulose gel is similar to that of the cellulose solution, suggesting that the gelation resulted from a physical cross-linking. The gels were composed of relatively stable network units with an average diameter of about 47 nm. At either a higher temperature (at 60 degrees C for 30 s) or a longer gelation time (at 30 degrees C for 157 s), the gel in the 5 wt % cellulose solution could form. A schematic gelation process was proposed to illustrate the sol-gel transition: the random self-association of the cellulose chains having the exposed hydroxyl in the aqueous solution promotes the physical cross-linking networks.     

Steady flow and viscoelastic properties of lubricating grease containing various thickener concentrations

The flow and viscoelastic properties of a lubricating grease formed from a thickener composed of lithium hydroxystearate and a high-boiling-point mineral oil were investigated as a function of thickener concentration. The flow properties of grease were measured using continuous shear rheometry, while the viscoelastic properties were measured using oscillatory shear measurements. The flow properties show that grease is a shear-thinning fluid with a yield stress that increases with thickener concentration. At concentrations of lithium hydroxystearate greater than 5% by volume, the storage modulus, G', was found to be greater than the loss modulus, G", with both moduli increasing with increasing thickener concentration, below this critical concentration G" was greater than G'. Slip at the wall of the measuring platens was a major problem encountered during the rheological measurement of grease, this is hardly surprising, and greases are designed to slip in their lubricating functions. Therefore the measuring platens were roughened by sandblasting and significantly higher yield values were recorded with the roughened geometries. Creep experiments were also performed. In the creep test, yield stresses of greases could be obtained. Zero shear viscosity was also calculated from the creep experiment and as a result viscosities over nine orders of magnitude were obtained. The power law index of the scaling law of the elastic modulus and yield stress with increasing volume fraction was found to be 4.7+/-0.2 suggesting that the flocculation of the particles that compose the grease is likely to be of the chemically limited aggregation variety.