Melt-state shear flow and elasticity of a thermoplastic fluorosulphonated—PTFE copolymer

Some rheological properties of a perfluorosulphonated PTFE copolymer have been measured in order to characterise the melt-state viscous and elastic behaviour of a thermoplastic precursor of Nafion®, an ion-selective membrane used in the electrochemical industry. Steady-state shear viscosity measurements show conventional pseudoplastic flow behaviour over a wide temperature range, under high shear conditions. These data have been modelled to a high level of accuracy using polynomial simulations to obtain Carreau model coefficients and flow activation energies. Using an orifice die in a capillary rheometer, calculated extensional viscosity data are shown to decrease with stress and are more temperature-sensitive than shear viscosity. Although die swell increases with shear rate in a conventional manner, unusual and complex die swell data (at a fixed shear stress) have been obtained in response to an increase in process temperature. This behaviour is attributed to the breakdown of a small-scale network of domains and ordered crystalline material in the amorphous matrix of the precursor, as exemplified by a very broad melting endotherm. Different modes of deformation have been proposed to explain the rheological data observed across the process temperature range. The observed changes to the flow mechanism and elastic character of the melt carry practical implications for the extrusion processes and developed microstructure of film products manufactured from this precursor copolymer.     

黏度指数改进剂HSD的增粘机理

对聚苯乙烯-氢化聚二烯嵌段共聚物(HSD)改性的150SN润滑基础油的性能进行了测试。研究表明HSD具有优异的增粘能力和抗剪切稳定性。动态激光光散射实验表明HSD在溶液中是以胶束形式存在,胶束的流体力学半径(Rh)对温度有依赖性。温度升高,HSD的流体力学半径逐渐增大,在45℃左右,流体力学半径突然减小。实验发现不同的溶剂有不同的转变温度,但变化趋势基本相同。动态流变测试表明随着频率的增加,加入HSD的基础油的弹性模量和损耗模量均增加。在低频时主要表现为弹性效应,高频时则主要表现为粘性效应。随着温度的升高,润滑油的损耗模量逐渐减小,其弹性模量在60℃左右有一个转折点。     

The role of viscosity in the impulse diffraction field of elastic waves induced by the acoustic radiation force

Several ultrasound-based techniques for the estimation of soft tissue elasticity are currently being investigated. Most of them study the medium response to dynamic excitations. Such responses are usually modeled in a purely elastic medium using a Green's function solution of the motion equation. However, elasticity by itself is not necessarily a discriminant parameter for malignancy diagnosis. Modeling viscous properties of tissues could also be of great interest for tumor characterization. We report in this paper an explicit derivation of the Green's function in a viscous and elastic medium taking into account shear, bulk, and coupling waves. From this theoretical calculation, 3D simulations of mechanical waves in viscoelastic soft tissues are presented. The relevance of the viscoelastic Green's function is validated by comparing simulations with experimental data. The experiments were conducted using the supersonic shear imaging (SSI) technique which dynamically and remotely excites tissues using acoustic radiation force. We show that transient shear waves generated with SSI are modeled very precisely by the Green's function formalism. The combined influences of out-of-plane diffraction, beam shape, and shear viscosity on the shape of transient waves are carefully studied as they represent a major issue in ultrasound-based viscoelasticity imaging techniques.     

低密度聚乙烯/氧化铁红色母料流变行为的温度效应

采用毛细管流变仪详细分析了LDPE/Fe2O3色母料在加工温度下黏度的变化情况。研究发现,温度对体系黏度的影响可用Arrhenius方程近似说明;随着温度的升高,色母料熔体黏度呈指数形式下降。用表观粘流活化能描述材料的粘温敏感性,并研究发现,随着粒子填充体积分数和剪切速率的增大,体系表观粘流活化能均有明显下降,且剪切速率对LDPE/Fe2O3色母料粘温敏感性的改变作用大于Fe2O3填充体积分数。     

Analysis of rheological properties of bone cements

The rheological properties of three commercially available bone cements, CMW 1, Palacos R and Cemex ISOPLASTIC, were investigated. Testing was undertaken at both 25 and 37 °C using an oscillating parallel plate rheometer. Results showed that the three high viscosity cements exhibited distinct differences in curing rate, with CMW 1 curing in 8.7 min, Palacos R and Cemex ISOPLASTIC in 13 min at 25 °C. Furthermore it was found that these curing rates were strongly temperature dependent, with curing rates being halved at 37 °C. By monitoring the change of viscosity with time over the entire curing process, the results showed that these cements had differing viscosity profiles and hence exhibit very different handling characteristics. However, all the cements reached the same maximum viscosity of 75 × 10³ Pa s. Also, the change in elastic/viscous moduli and tan δ with time, show the cements changing from a viscous material to an elastic solid with a clear peak in the viscous modulus during the latter stages of curing. These results give valuable information about the changes in rheological properties for each commercial bone cement, especially during the final curing process.     

不同分子量丙烯腈-丙烯酰胺共聚物溶液的流变性研究

将不同分子量的丙烯腈（AN）与丙烯酰胺（AM）的共聚物溶解于二甲亚砜（DMSO）中，获得聚丙烯腈（PAN）溶液。采用旋转粘度计和锥板流变仪，从非牛顿指数n、流动活化能△Eq、结构粘度指数△ηa和弹性模量G等方面比较了不同分子量PAN溶液的流变性能。结果表明，分子量高的PAN溶液的表观粘度对应力变化敏感，分子理低的PAN溶液的表现粘度对温度的变化敏感，无论是从粘性还是从弹性角度看，低分子量PAN溶液的物理稳定性好。     

Measurement of the properties of fluids inside pipes using guided longitudinal waves

A new technique for measuring the longitudinal bulk velocity and shear viscosity of a fluid contained inside a pipe without a need for extracting a sample from inside of the pipe is presented. It is based on the measurement of the change of the dispersion properties and attenuation of longitudinal guided modes propagating in the pipe due to the presence of the fluid. The technique to extract longitudinal bulk velocity and shear viscosity is discussed and experimentally demonstrated by measuring both low-viscosity (distilled water and glycerol) and highly viscous fluids. The measured properties of glycerol agreed well with conventional methods and literature data for both the longitudinal bulk velocity (within 0.8%) and the viscosity (within 4%). For highly viscous fluid, the accuracy of the velocity measurement was found to be reduced slightly (within 1%), and the viscosity measurement became more accurate (within 1%).     

乙烯共聚聚丙烯流延膜树脂的凝聚态和流变特性

研究了均聚聚丙烯流延膜树脂(CPP)和含乙烯的无规共聚聚丙烯流延膜树脂(CEPP)的结构与加工性能,采用差示扫描量热(DSC)研究CPP和CEPP结晶和熔融性能;以毛细管流变仪研究CPP和CEPP的熔体黏度与剪切应力关系及剪切速率、乙烯含量和粘流活化能的关系.研究发现,随着乙烯含量的增加,CEPP的热封温度降低而软包装...     

The measurement of bulk viscosity and the elastic-viscous analogy

Summary The motion of a liquid containing a substantial volume fraction of gas bubbles can often be calculated by considering a suitably averaged single phase continuum. This averaged material will be compressible as well as viscous and the problem arises to the determination (by experiment) of its shear and bulk viscosity coefficients. The direct measurement of bulk viscosity would be difficult, and the usual approach has been to measure an apparent elongational viscosity and then appeal to an analogy between elasticity and viscosity, claiming a connection similar to that which holds between the various elastic moduli. It is shown that this analogy does not hold in compression and that the experiments must be reinterpreted more carefully.     

Influence of visco-elastic binder properties on ram extrusion of a hardmetal paste

The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide–cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30–42 °C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow–Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, σ₀, increased linearly with the binder elastic modulus, G′, while both the velocity dependence parameters α and β were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2–5 particle diameters.     

Viscoelasticity of Maxwell's model and non‐Newtonian viscosity revisited

The viscosity of fluids and melts is an important characteristic to steer processes and reactions of materials, to use lubricants and to fabricate diverse products of glass. To steer such fabrication processes reliably and free of failures one necessarily needs to understand and use the true data of the viscosity. The forces applied to measure the viscosity act also to accelerate parts of the samples and particularly to deform them elastically. To evaluate the viscosity one must necessarily consider such ‘side reactions’. Cylindrical samples under longitudinal deformation are demonstrated to deform rather elastically than by viscous flow upon application of the load, e. g. Neglecting this effect the ’viscosity’ apparently decreasing with increasing load may be misinterpreted as non‐Newtonian viscosity. In fact, it represents the change from viscous to elastic behaviour with decreasing time interval of the application of force. Furthermore, production of entropy during deformation for measurement has to be taken into account adequately. The sample warms up during heavy deformation. If the viscosity depends strongly on the temperature, one must take into account that temperature and viscosity change with the intensity of the load. Then the so called ’shear thinning’ is rather ’sheer heating’. This is demonstrated quantitatively with data of the viscosity as a function of the load, which have recently been published using capillary rheometers.     

Effective rheological properties of a disperse mixture of viscoelastic materials

The article deals with the problem of determining the compressive and shear moduli, and also the shear and bulk viscosity of a viscoelastic medium with spherical inclusions of some other viscoelastic material. Calculations are presented for an elastic medium with inclusions of a viscous liquid.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 50, No. 3, pp. 434–445, March, 1986.     

Explicit Corrections for the Effect of Viscous Heating in Circular Couette Viscometers

Based on asymptotic solutions to the problem of coupled flow and heat transfer in circular Couette flow of materials whose viscosity and thermal conductivity are polynomial functions of temperature, we obtain expressions for the effect of viscous heating on the gapwise distribution of shear rate under isothermal and adiabatic wall conditions. These expressions are shown to exhibit the anticipated asymptotic behavior as the gap-to-diameter ratio approaches unity and are in agreement with numerical results for a reasonable range of the Nahme number. Following that, we derive explicit rheological corrections for circular Couette–Hatschek viscometers; these account for the effect of viscous heating in the presence of temperature-dependent fluid properties and are reliable for values of the correction factor down to around 0.8.     

反应性弹性体三元共聚物改性沥青及其混合料性能与机制

采用黏度试验和动态剪切流变试验研究了反应性弹性体三元共聚物（RET）对基质沥青与苯乙烯-丁二烯-苯乙烯嵌段共聚物（SBS）改性沥青性能的影响,通过原子力显微镜（AFM）分析了SBS改性沥青和RET-SBS改性沥青的表面形貌特征,并采用车辙试验、低温弯曲试验、弯曲疲劳试验及加速加载试验评价了RET改性沥青混合料的各项技术性能,最后通过Weibull分布,分析了不同RET改性沥青混合料在不同失效概率下的疲劳性能。结果表明：RET的掺入提高了沥青的黏度和抗车辙因子,对沥青的高温性能有较大改善;通过掺入RET-SBS,增加了改性沥青中的黏性成分;相较于SBS改性沥青,RET-SBS改性沥青的表面粗糙度显著增大;RET改性剂能够明显改善沥青混合料的高温稳定性;RET与SBS改性剂复配,可有效弥补RET对沥青混合料低温性能的不足,明显改善沥青混合料的疲劳性能和高温长期稳定性。     

In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.     

The influences of particle–particle interaction and viscosity of carrier fluid on characteristics of silica and calcium carbonate suspensions-coated Twaron® composite

The effects of particle–particle interaction and viscosity of carrier fluid on steady and dynamic rheological responses and quasi-static penetration resistance of Twaron® fabrics treated with shear thickening and shear thinning suspensions have been investigated. The suspensions have been made by mechanically dispersing 60 nm silica (SiO₂) and calcium carbonate (CaCO₃) nanoparticles in poly ethylene glycol (PEG) with molecular weights of 200 and 400 g/mol. The CaCO₃ suspensions display shear thinning behaviour along with the total dominance of the elastic state over the viscous state while the SiO₂ suspensions exhibit shear thickening behaviour with the emergence of both the elastic and viscous states. With the increase of molecular weight of PEG, viscosity, viscoelastic modules and instability of the suspensions increase and critical shear rate and frequency of transition to elastic state diminish. The PEG200 and PEG400-contained SiO₂ suspensions-treated Twaron® composites at 35 wt.% have quasi-static penetration resistances which are nearly 2.63 and 2.48 times and maximum absorbed energies which are about 1.54 and 1.55 times higher, respectively, than those of the corresponding CaCO₃ ones. However, the influence of increasing the PEG's molecular weight is not as considerable as the effect of particle–particle interaction on the enhancement of penetration resistance performance.     

Particulate size effect on the rheology of SiC-glass composites

The rheological behavior of SiC particulate glass composites was investigated in the present study. The nature and extent of flow modifications are addressed with respect to solid content in the suspension, temperature and dispersoid size. A transition from Newtonian to non-Newtonian viscous flow and characteristic shear thinning behavior were observed. With progressive strengthening and deviation from Newtonian flow, a significant loss in rate sensitivity occurred. The apparent viscosity of the composites increased with the concentration and size of reinforcements. The increase in viscosity is explained in terms of hydrodynamic/mechanical interactions between particles in the composites.     

Comparison of the flow properties of aqueous suspension corticosteroid nasal sprays under differing sampling conditions

Many aqueous suspension corticosteroid nasal sprays become less viscous when shaken and sprayed, then return to a more viscous state after application. This time-dependent, reversible loss of viscosity under shear (e.g., shaking or spraying) can be quantified in the rheological property of thixotropy. The flow properties of 5 corticosteroid nasal sprays were measured over a range of shear rates. The formulations tested included Nasonex, Vancenase AQ, Nasacort AQ, Rhinocort Aqua, and Flonase. The yield stress values, as well as an estimate of thixotropy, were compared by using three different sampling techniques, including one that simulated patient use (shaking for 30 sec, spraying, and immediately transferring the sample to the rheometer). The rheological properties of all products indicated that when initially shaken and dispensed, they flowed more freely, followed by recovery of viscosity that would likely inhibit the suspensions from flowing out of the nasal cavity. Under all three tested conditions, Nasonex exhibited the highest yield stress, the largest apparent initial and final viscosities, and the highest apparent thixotropy. The study protocol that simulated patient-use conditions produced the following rank order of measured thixotropy: Nasonex > Flonase > Vancenase AQ > Rhinocort Aqua > Nasacort AQ. The thixotropy of Nasonex was 3.4 to 21.4 times greater and the final viscosity was 3.2 to 17.4 times greater than the values of the other tested products.     

温度对HSG冻胶体系流变性的影响

测量了HSG冻胶体系的屈服应力、蠕变-回复和粘弹性参数，研究了温度对其流变性的影响．结果表明，HSG冻胶体系的屈服应力随着温度的升高而明显下降，超过冻胶体系屈服应力之后很快达到稳定的平衡应力值，温度对其影响很小．温度越高，冻胶的柔量越大，越易变形．HSG冻胶体系具有高弹低粘特性，随着温度的升高、冻胶弹性明显下降，但粘性下降不大．温度越高、冻胶线性粘弹性区域越小．     

Study on SH-SAW in imperfectly bonded piezoelectric structures loaded with viscous liquid

We analytically investigate shear horizontal surface acoustic wave (SH-SAW) propagation in layered piezoelectric structures loaded with viscous liquid, which involves a thin piezoelectric layer imperfectly bonded to an unbounded elastic substrate. The coupling wave equations are obtained based on the linear piezoelectric theory. The governing equations are solved by means of the analytical method with consideration of electrically open and shorted cases, respectively. The dispersive relations are obtained, and the effects of the imperfect constant on the properties of waves are presented and discussed. From the numerical results, we can find that the phase velocity decreases with the increase of the interface parameter n, and for a specified viscosity, the attenuation increases with the interface parameter. The results show that the effects of the imperfect constant on the properties of SH-SAW are remarkable.