一种测试剪切黏度与拉伸黏度的方法

基于一种新型黏度模型,并通过实验证明了该黏度模型的可行性。采用截面渐变收缩的拉伸流动实验,从实验和数值计算两方面分别研究了牛顿流体和非牛顿流体的剪切黏度和拉伸黏度。同时,从实际加工生产的角度出发,强调了聚合物实际加工过程中真实黏度的重要性,并提出黏度具有唯一性的原理。采用几种常见的商业流变仪,测试了相同材料的剪切黏度与拉伸黏度,通过比较发现,新的黏度测试方法具有一定的合理性,为开发大应变速率范围的、复合流动的流变仪研究提供了理论依据。     

辐照处理对玉米醇溶蛋白流变性的影响

为了改善玉米醇溶蛋白在复合材料加工中的流变特性,研究了辐照剂量、温度、剪切速率对玉米醇溶蛋白流变性的影响。结果表明,玉米醇溶蛋白经辐照处理后具有假塑性流体特性,呈现"剪切变稀"现象。辐照剂量、剪切温度和剪切速率对玉米醇溶蛋白的流变性有显著影响。随着辐照剂量增加,溶液黏度呈现先增加后减小的趋势,当辐照剂量为10kGy时,黏度最高;随着剪切温度的增加,溶液黏度呈现先下降后增加的趋势,当温度为308K时,黏度最低;随剪切速率的增加,溶液的黏度降低,但当剪切速率接近100s-1时,黏度变化不明显。     

Continuous shear thickening and discontinuous shear thickening of concentrated monodispersed silica slurry

Concentrated slurry is known to exhibit shear thickening behavior, in which viscosity increases as the shear rate ascends. However, to identify the differences between this shear thickening behavior and rapid increases in viscosity (such as the dilatancy behavior of starch, sand, and other concentrated slurries) and the smooth increases in viscosity exhibited by concentrated slurries, this research investigated the rheological behavior of a polyethylene glycol suspension containing monodispersed silica particles with a size of 2.5 μm. The results found that the increases in viscosity as the shear rate ascends or the increases in elasticity as the strain ascends change consecutively from smooth and reversible behavior (i.e., continuous shear thickening (CST)) to rapid and irreversible behavior (i.e., discontinuous shear thickening (DST)) simply by increasing the concentration of the slurry, even in the case of concentrated slurries comprising of the same particles. DST is a manifestation of dilatancy in which a jamming transition occurs due to collisions between particles. Because CST transitions successively to DST, and the on-set shear stress of shear thickening of CST is almost the same with that of DST, shear thickening in the CST region may, therefore, also be regarded as the result of friction due to collisions between particles. This supports the research by Seto, Mari, Poon et al., which stated that shear thickening occurs due to friction from particle collisions.     

Mechanisms of viscosity increase for nanocolloidal dispersions

An EMD model for nanocolloidal dispersions considering the interaction between atoms within solid particles is developed for viscosity calculation and studying the effect of the particle size and volume fraction. Strong oscillations are observed in the pressure tensor autocorrelation function. Elimination of this oscillation is achieved by adjusting the potential among atoms of nanoparticles to reduce the acoustic mismatch between particles and liquid. The shear viscosity of nanocolloidal dispersion is found strongly dependent on the particle size, which cannot be predicted by traditional effective medium theory. Through decomposing of the pressure tensor, the viscosity contribution from interactions between liquid-solid atoms and solid-solid atoms are believed to dominate the viscosity increase of colloidal systems. Our model reveals the shear viscosity increase mechanism at the molecular-level and predicts that the shear viscosity of simple colloidal dispersions reaches a plateau value when the particle size becomes large enough.     

Applicability of the rheological equation of state for thermoplastic composites

A simple experimental method for determining the steady-state shear viscosity of thermoplastic composite melts has been used. Using this method, we have determined the steady-state shear viscosity of an automotive thermoplastic composite system, namely, wollastonite-filled poly(ethylene terephthalate) (WFPET), at various temperatures and shear rates. All the viscosity properties investigated can be successfully described and predicted by a thermodynamically based rheological equation of state. The effects of composition and mixing conditions on the steady-state shear viscosity of all the WFPET investigated were also determined using this rheological equation of state.     

Rheology and flow-induced liquid crystal phase transitions in thermotropic polyethers

This work investigates the interdependence of the phase behaviour, viscosity, temperature, molecular weight and shear rates of thermotropic liquid crystalline polyethers. The viscosity of the isotropic and nematic phases are quantitatively compared; a positive variation in viscosity with respect to temperature is found, with the isotropic viscosity being about an order of magnitude higher than the liquid crystalline viscosity. The dependence of viscosity upon molecular weight of well defined fractions is investigated in both the liquid-crystal and isotropic phases. In the liquid crystalline state the viscosity scales with M ^3.5–5. Variations in the viscosity due to temperature changes affect the isotropic phase more than the liquid crystal phase. No evidence for a negative first normal stress difference is seen. Finally, it is shown how the phase diagram of the material can be altered by shearing the material in the isotropic phase. This is evident by the onset of a shear thinning region at temperatures slightly above T _i, which can be attributed to the formation of shear induced liquid crystallinity.     

Multiple shear step approach to determine the rotational viscosity of asphalt emulsions and its correlation with water content of original and diluted emulsions

Viscosity determination of thixotropic emulsions with good repeatability has always been a major challenge. Currently, Saybolt Furol viscometer (SFV) is used to determine the viscosity of the emulsion, but the main drawback of the SFV is that it cannot simulate the behaviour of emulsion under different shear rate. Rotational viscometer (RV) can measure viscosity at different shear rates. Due to the thixotropic behaviour of the emulsions, getting repeatable results by following the hot binder specification is a problematic task. In this study, a new multiple shear step approach is used to determine the viscosity of the emulsified asphalt using RV. Three low viscous (SS-1, SS-1H and SS-1L) and two high viscous (CRS-2 and CRS-2P) emulsions were used in this study. Shear stress is gradually stepped up to different levels after certain time interval to determine the viscosity. In this manner, emulsion undergoes a known shear state and each reading is preceded by a certain repeatable shear history. It was observed that with the progression of time and simultaneous increase in shear rate, the viscosity results are much more stable and repeatable with less than 5% coefficient of variance. The final specifications proposed are 220–730 and 5–90 cP at 50 rpm and 30 °C for high and low viscous emulsions, respectively, which are based on 98% probability. Viscosity measured by this approach also showed strong correlation with water content (R² > 0.94). The correlation between viscosity and water content is even stronger after dilution. With different dilution water content, viscosity of CRS-2 and CRS-2P exhibited R² values of 0.97 and 0.98, respectively.     

Transport and relaxation properties of superfluid 3He. II. Viscosity,thermal conductivity,and relaxation of the normal fluid density

The kinetic equation for Bogoliubov quasiparticles is solved in a well-controlled approximation and the kinetic coefficients of shear viscosity, second viscosity, and thermal conductivity are calculated for all temperatures. The results are in good agreement with data on the shear viscosity. Finally, the rate of relaxation of the normal fluid density from a state of disequilibrium with the superfluid component is considered.Also at Max-Planck-Institut für Physik und Astrophysik, München, Germany.     

改性聚氨酯防水材料的流变性能

利用RS150型平板流变仪测试了改性聚氨酯防水材料的表观黏度、粘流活化能、非牛顿指数等流变参数,讨论了剪切速率、剪切应力和温度等对改性聚氨酯防水材料表观黏度的影响。实验结果表明,改性聚氨酯防水涂料的表观黏度随温度的升高而降低;在实验温度范围中,改性聚氨酯防水材料的表观黏度随剪切速率和剪切应力的增大而降低,其非牛顿指数n小于1,并且随着温度升高而增大,表明改性聚氨酯防水材料为假塑性流体;其粘流活化能E0为19.73 kJ/mol。     

Investigation of the flow behaviors of carbon nanotubes dispersed epoxy resin with modified bi-mode FENE dumbbell simulation

In this study, a modified bi-mode finitely extensible non-linear elastic (FENE) dumbbell model was introduced to investigate the concentration-dependent and shear-rate-dependent viscosity of carbon nanotubes (CNTs) dispersed polymer solutions. It is called bi-mode because the aggregated CNTs and free CNTs are considered as two different types of CNTs with different mobility. The diffusion coefficient was simulated by classical molecular dynamics (MD) simulation and input into the FENE models. For the steady shear flow, the coupled Fokker–Planck equations and the corresponding stress tensors were solved numerically. The influence of CNT diameter and CNT mass on the shear viscosity was discussed. In addition, the bi-mode FENE dumbbell simulation can be applied to investigate the shear viscosity under different shear rates and increase of shear viscosity with time evolution. With the model, the influence of the anisotropy parameter, finite extensibility parameter was investigated. The shear-rate-dependent viscosity profile of resin solutions with different CNT concentrations was also predicted and validated with experimental rheological behavior. The simulation model can provide qualitative prediction of rheological behavior of CNTs dispersed resin.     

全同聚1-丁烯/低密度聚乙烯共混体系的流变性能

采用双毛细管流变仪研究了全同聚1-丁烯/低密度聚乙烯(iPB/LDPE)共混体系的流变性能。结果表明,随着iPB用量的增加,共混熔体的剪切黏度呈先下降后上升的趋势;iPB/LDPE共混熔体在剪切速率为100 s-1~1000 s-1时,为假塑性流体,且随着iPB含量增加和温度升高,其非牛顿性增大;共混体系的表观黏度随剪切速率和剪切应力的增大、温度的升高而减小;粘流活化能随剪切速率的增大呈逐渐减小的趋势。     

Apparatus for Simultaneous Small Angle Neutron Scattering and Steady Shear Viscosity Studies of Polymer Melts and Solutions

The design and construction of an apparatus for studying the simultaneous small angle neutron scattering (SANS) and steady shear viscosity behavior of polymer melts and concentrated solutions is discussed. Successful operation of the device is demonstrated on a blend of 20 weight percent deuterated polystyrene and 80 weight percent poly(vinylmethylether). The effects of shear on the critical behavior of the blend are observed in the SANS behavior as a function of temperature and shear rate and indicate shear induced mixing behavior for the range of shear rates examined. The steady shear viscosity results alone are insufficient for detecting the transition from one to two phases. The examination of shear effects in polymer blends is important for understanding the critical behavior of binary systems. Technologically, knowledge of the phase behavior of polymer blends under shear are important for the design and improvement of commercial blend processing.     

Effect of addition of polycarbonate on sheared flow of red mud-filled isotactic polypropylene

Different volume fractions of polycarbonate (PC) were incorporated to improve thermal stability of red mud (RM) filled polypropylene (PP). Effects of PC addition in RM filled PP on shear stress, melt viscosity, and melt elasticity have been determined under different shear rates by using a capillary rheometer. With the increase in shear rate, addition of PC in RM-filled PP reduced its shear stress and melt viscosity. However, recoverable shear strain increased with PC content in the blend.     

Numerical 2D models of consolidation of dense flocculated suspensions

A mathematical 2D model for a consolidation process of a highly concentrated, flocculated suspension is developed. The suspension is treated as a mixture of a fluid and solid particles by an Eulerian two-phase fluid model. The suspension is characterized by constitutive relations correlating the stresses, interaction forces, and inter-particle forces to concentration and velocity gradients. This results in three empirical material functions: a permeability, a non-Newtonian viscosity and a non-reversible particle interaction pressure. Parameters in the models are fitted to experimental data. A simulation program using finite difference methods both in time and space is applied to one and two dimensional test cases. The effect of different viscosity models as well as the effect of shear on consolidation rate is studied. The results show that a shear thinning viscosity model yields a higher consolidation rate compared to a model that only depends on the volume fraction. It is also concluded that the size of the viscosity influences the time scale of the process and that the expected effect of shear on the process is not weil reproduced with any of the models.     

Flow of electro-rheological materials

Summary An electro-rheological fluid is a material in which a particulate solid is suspended in an electrically non-conducting fluid such as oil. On the application of an electric field, the viscosity and other material properties undergo dramatic and significant changes. In this paper, the particulate imbedded fluid is considered as a homogeneous continuum. It is assumed that the Cauchy stress depends on the velocity gradient and the electric field vector. A representation for the constitutive equation is developed using standard methods of continuum mechanics. The stress components are calculated for a shear flow in which the electric field vector, is normal to the velocity vector. The model predicts (i) a viscosity which depends on the shear rate and electric field and (ii) normal stresses due to the interaction between the shear flow and the electric field. These expressions are used to study several fundamental shear flows: the flow between parallel plates, Couette flow, and flow in an eccentric rotating disc device. Detailed solutions are presented when the shear response is that of a Bingham fluid whose yield stress and viscosity depends on the electric field.     

聚丙烯腈/二甲基亚砜纺丝原液流变性及流变方程拟合

以高黏均分子量(-Mη)聚丙烯腈(PAN)为研究对象,系统研究了黏均分子量(-Mη,以下简称分子量)、温度(T)、固含量(wt)和剪切速率(γ)对聚丙烯腈(PAN)/二甲基亚砜(DMSO)纺丝原液流变性能的影响。结果表明,纺丝原液分子量和剪切速率皆存在一个临界值。在临界值之前,表观黏度随分子量增加迅速增大,随剪切速率的增加迅速降低,在临界值之后,变化趋势均趋于平缓;且临界值不随温度变化而改变;依据试验结果进行表观黏度与四因素线性相关方程拟合,经对比,计算值与实验值相差不大,可以为纺丝原液表观黏度的预测和后续纺丝工艺的改进提供理论参考。     

The Effect of Friction on Wide Shear Bands

Frictional and frictionless granular materials in a split-bottom ring shear cell geometry show wide shear bands under slow, quasi-static deformation. Here, the differences between frictional and frictionless materials are elaborated using discrete element simulations (DEM). Several continuum fields like the density, the velocity field, the deformation gradient, and the stress are used here for comparison.

Interestingly, the shear stress intensity, i.e., the shear stress divided by the pressure, is approximately constant throughout the wide shear band, as long as the strain rate is large enough—indicating a Mohr-Coulomb type yield stress fluid. The “viscosity,” i.e., the shear stress divided by the strain rate, is proportional to the pressure, which is increasing with the contact number density. Furthermore, the viscosity is inversely proportional to the nondimensional strain rate, indicating shear softening behavior inside the wide shear bands.     

影响柔性版印刷水基油墨粘度的因素分析

在分析柔性版印刷水墨在传输转移过程中的流变特性的基础上,研究了剪切应力、剪切速率、屈服值、油墨颜料粒子、表面活性剂以及温度等对柔性版水基油墨粘度的影响.结果表明,剪切应力、剪切速率和屈服值对水基油墨的粘度有直接影响,总体上可以用Carreau 模型来描述.表面活性剂等助剂的加入通过对颜料体积浓度和油墨屈服值的影响,间接影响油墨粘度.