Electrorheological fluid characterization via a vertical oscillation rheometer

A custom designed vertical oscillation rheometer (VOR) is used for the rheological measurements of electrorheological (ER) fluids consisting of 15 and 20 vol.% semiconducting polyaniline particles suspended in silicone oil. The viscoelastic material functions, including complex viscosity and complex shear modulus, are measured via geometric parameters, measured force, and applied strain of the VOR. Viscoelastic properties of the ER fluids are also measured as a function of applied electric field strength and particle concentration. The VOR, equipped with a high voltage generator, can easily be constructed and used to measure ER properties. It is further found that polyaniline suspensions behave as viscoelastic materials in an electric field. In linear viscoelastic conditions, elasticity was promoted with the increment of electric field due to particle chain structure in the presence of the applied electric field. It is also found that the applied electric field rather than particle concentration enhanced the elasticity of ER fluids.     

茂金属聚乙烯和低密度聚乙烯共混物的流变行为

研究了茂金属催化乙烯丁烯1共聚物mPE和LDPE共混物的流变行为.测定了一系列共混物的稳态剪切粘度和动态粘弹性,用改进Cross模型拟合实验数据.mPE的零切粘度η₀较小,从牛顿型转变为非牛顿型所需的剪切速率较大,转变应力较高,在挤出加工剪切速率范围内熔体粘度高,对剪切敏感性差,这是由于它有较低的重均分子量、窄的分子量分布(M_w/M_n=21)所致.对于对数加和规律,共混物η₀在mPE/LDPE为50/50和25/75时有强烈的正偏差,这是由于共混物自由体积减小所致.共混物的转变应力τ^*和非牛顿指数n随LDPE加入量增大而降低,表明共混物对剪切的敏感性提高,加工性得到改善.G'和G”的一致性说明mPE和LDPE共混是相容的.     

Influence of NaClO3 on the rheological behaviour of a micellar solution of CPCl

It is now well know that a small addition of salt to a micellar solution often increases the zero-shear viscosity η₀ of the solution, the understanding of the behaviour at high salt content is more questionable. In this situation, addition of more salt induces a decrease of η₀. In this experimental work we investigate the linear and non-linear rheological behaviour of a new micellar system: CPCl (surfactant)/NaClO₃ (salt). Studies of the evolution of η₀ as well as G₀ (the elastic modulus) or τ_R (the relaxation time) are in agreement with the hypothesis of a diminution of the mean micellar length when, after the maximum η₀, the salt content increases. In the non-linear behaviour (non-Newtonian viscosity) the evolution of γ˙ _c, (which defines the occurrence of the shear thinning) with salt concentration C_S is also in agreement with such a hypothesis. Received: 29 March 1999/Accepted: 20 March 2000     

EFFECT OF PAN-MILLING ON RHEOLOGICAL PROPERTIES OF HIGH DENSITY POLYETHYLENE*

The effect of pan-milling on the rheological properties of high density polyethylene (HDPE) was studied. Aninnovative milling apparatus, viz. an inlaid pan-mill, was used. Melt indexer, capillary rheometer, Haake Rheocord 90 single-screw extruder and Brabender rheometer were used to evaluate the rheologieal properties of HDPE. HDPE with higher initialmolecular weight and larger particle size was easier to degrade under pan-milling stress, as indicated by the melt index.Pressure oscillation in capillary flow occurred at significantly higher shear stress and shear rate for milled HDPE than forunmilled HDPE. The apparent shear viscosity of HDPE decreased with increasing times of milling. After milling, the flowactivation energy decreased and thus the sensitivity of viscosity to temperature was reduced. Die pressure and torque duringsingle screw extrusion were reduced significantly after milling. Plasticizing time as measured in a Brabander mixer decreasedmarkedly with increasing milling times.     

聚丙烯酸十八酯-乙酸乙烯酯梳状二元共聚物降凝剂对含蜡原油结晶特性与流变性的影响

在合成聚丙烯酸十八酯(POA)梳状均聚物和聚丙烯酸十八酯-乙酸乙烯酯(POA-VA)系列梳状二元共聚物的基础上,通过凝点测量、流变实验、差示扫描量热(DSC)分析及偏光显微镜观察等手段研究了POA与POA-VA对长庆含蜡原油结晶特性与流变性的影响.实验结果表明VA基团的引入调控了POA降凝剂对含蜡原油的作用效果.当OA与VA单体摩尔比为3∶1时,POA-VA对含蜡原油的流变改善效果最好,在降凝剂400 mg/kg剂量下可以降低凝点22℃,平均降黏率为51.45%;而单体摩尔比升高或降低均会使POA-VA对含蜡原油的流变改善效果变差.另外,从POA-VA分子的结晶放热特性和蜡晶微观形貌分析角度,探讨了VA含量对POA-VA作用性能的影响规律和机理.     

钒氧化物纳米管的合成、结构及电化学性能

采用流变相-纳米自组装新方法合成了钒氧化物纳米管(VO_x-NTs),并通过XRD,SEM,TEM,Raman,ESR,TG-DTA,XPS及模拟电池等技术手段对产物的结构和性能进行了表征和测试.结果表明,产物主要由钒氧化物纳米管组成,纳米管长为1～10μm,直径为30～100nm.纳米管壁由3～10个VO_x层构成,层间距为3.53nm.Raman光谱反映了V-O的伸缩或弯曲振动,层状微结构的晶格振动及模板剂的有机基团振动.无明显精细结构的室温ESR谱证明了V⁴⁺的存在,根据TGA和XPS求得产物中V的平均化合价约为+4.30.VO_x-NTs正极材料初始充电容量达到404mA.h/g,放电容量为383mA.h/g,50次循环后放电容量衰减至180mA.h/g,可归因于充放电过程中VO_x-NTs正极材料在电解液中的溶蚀作用及复合电极中“孤岛效应”的产生.     

Rheological properties of wood polymer composites at high shear rates

This paper presents the rheological properties of wood-polymer composites (WPC) with a polypropylene (PP) matrix in the corrected shear rate range from approx. 20 s⁻¹ to 150 000 s⁻¹. Tests were conducted using a capillary rheometer and a rheological head of the author's construction, for which the working element is a thermoplastic injection moulding machine. The constructed tool was found to be very useful, especially for the determination of the processing characteristics of WPC composites containing a large particle-size filler. It was observed that the rheological properties of wood-polymer composites in the shear rate range of up to several thousand s⁻¹ significantly depended on the filler content of the polymer matrix; at the same time, at higher shear rate, a clear decrease in the effect of the wood filler content on the viscosity of the composites and on the flow behaviour, as described by the power law, took place.     

大口径离轴凸非球面的加工和检测

将光学系统波像差检验技术与子孔径拼接测试技术相融合提出了凸非球面系统拼接检测方法,对该方法的原理和实现步骤进行了分析和研究,并建立了合理的子孔径拼接数学模型.依次利用计算机控制光学表面成形技术和磁流变抛光技术对一包含大口径凸非球面的离轴三反光学系统的各反射镜进行加工,并对整个系统进行装调和测试.测定光学系统各视场的波像差分布,通过综合优化子孔径拼接算法和全口径面形数据插值求解得到大口径凸非球面全口径的面形信息.结合工程实例,对一口径为292mm×183 mm的离轴非球面次镜进行了系统拼接测试和加工,其最终面形分布的均方根值为0.017λ(λ=632.8 nm).     

超声辐照下聚乙烯熔体挤出流变特性的研究

研究了超声辐照作用下HDPE和LLDPE的挤出流变特性。结果表明,超声辐照可以促进聚乙烯分子链段的运动,降低熔体的挤出口模压力和表观粘度,明显提高聚乙烯熔体的流动性,使挤出物外观质量明显提高,为改善聚乙烯的加工性能及制品质量提供了新途径。     

Influence of rheological additives on char formation and fire resistance of intumescent coatings

Styrene-butyl acrylate copolymer based fire retardant coatings were prepared using intumescent flame-retardant additives and mineral clay type rheological additives. Three different widely used nanoclays, organic-modified montmorillonite, palygorskite and sepiolite were applied in order to determine their effect on the flame retardancy. Significant differences were found when their heat-shielding activities were evaluated. It was observed that the addition of different clay particles in amount of 0.25 w% changes the char formation process; the height, the morphology, the structure and also the mechanical resistance of the protecting shield. The different geometry and composition of the additives induced different changes in fire performance. In case of palygorskite the catalytic effect of Fe accelerated mainly the thermal decomposition, therefore the fire resistance decreased. The plate-like montmorillonite reduced the extent of the intumescent char, whereas also improved the mechanical and sustained heat resistance of the fire protecting shield. The fibrous sepiolite of low Fe content assisted the development of efficient protecting shield, which exhibited optimal cell structure, suitable thickness, and thus ensured better heat-insulating performance. Consequently, fire retardant effect of sepiolite was found to be better than the other studied clay types.