EFFECTS OF LIQUID VISCOSITY ON RHEOLOGY OF CONCENTRATED SUSPENSIONS

ABSTRACT

This paper presents the experimental results on the effects of liquid viscosity on the rheology of concentrated suspensions of solid particles in Newtonian liquids. Specifically, the relative viscosity of a pseudoplastic suspension decreases as the viscosity of the suspending liquid increases, indicating excess energy dissipation in a less viscous liquid. In contrast, the relative viscosity of a Newtonian suspension is only slightly affected by the liquid viscosity. It is in excellent agreement with the value predicted from the rigid sphere model which neglects nonhydrodynamic interactions, and assumes zero particle-to-liquid relative velocity. The flow behavior indices of both concentrated suspensions are independent of the liquid viscosity.     

Stream spreading in multilayer microfluidic flows of suspensions

The goal of this experimental study is to quantify the spreading of parallel streams with viscosity contrast in multilayer microfluidic flows. Three streams converge into one channel where a test fluid is sheathed between two layers of a Newtonian reference fluid. The test fluids are Newtonian fluids with viscosities ranging from 1.1 to 48.2 cP and suspensions of 10-mum-diameter PMMA particles with particle volume fractions phi = 0.16-0.30. The fluid interface locations are identified through fluorescence microscopy. The steady-state width of the center stream is strongly dependent on the viscosity ratio between the adjacent fluids and exhibits a near power-law relationship. This dependence occurs for both the Newtonian fluids and the suspensions, although the slopes differ. The high-concentration suspension (phi = 0.30) diverges from Newtonian behavior, while the low-concentration suspensions (phi = 0.16, 0.22) closely approximate that of the Newtonian fluids. The observed suspension behavior can be attributed to shear-induced particle migration.     

球形NQ对DNAN基熔铸炸药流变性能的影响

为研究硝基胍（NQ）球形化对2,4-二硝基苯甲醚(DNAN)/NQ体系流变性能的影响,采用旋转黏度仪研究了固体质量分数、剪切速率、颗粒形状及级配、工艺温度等因素引起的DNAN/NQ悬浮体系表观黏度的变化规律。结果表明:随着悬浮液固体质量分数的增加,表观黏度呈先缓慢增加至拐点再急剧增加的趋势,球形NQ与级配球形NQ在DNAN中的临界固体质量分数分别为55%和70%;固体质量分数越高,DNAN/NQ悬浮体系表观黏度受剪切速率的影响愈发明显,假塑性程度越高;相同条件下,颗粒越不规则,悬浮液体系越偏离牛顿流体,颗粒级配可有效降低悬浮液体系的假塑性程度;Arrhenius方程可精确描述DNAN/球形NQ悬浮液在96~115 ℃时表观黏度与温度的关系,悬浮液固体质量分数由0增加至41.18%时,流动活化能由36.69 kJ/mol增加到47.59 kJ/mol,悬浮液体系表观黏度相对温度变化越敏感。     

Antisymmetric stresses induced by the rigid-body rotation of dipolar suspensions: Vortex flows

It is shown theoretically that the steady rotation of a container filled with a spatially uniform suspension of identical, otherwise neutrally buoyant, dipolar spherical particles in a Newtonian fluid, each containing an embedded gravitational dipole (due to an assumed mass inhomogeneity within the sphere), will give rise to an antisymmetric stress state on the length scale of the suspension. Simultaneously, an external torque must be continuously exerted on the container by some agency to maintain its steady rotation. These phenomena obtain despite the fact that the suspension-scale motion is trivially a rigid-body rotation. This result is interpreted within the general framework of classical structured continua/director/micropolar fluid theories, supplemented with a mass distribution polarization density field. For the case of concentrated suspensions of spheres whose centers are arrayed in a cubic lattice (but are otherwise free to rotate about axes through their centers), expressions are obtained for all of the parameters required for a complete characterization of the phenomena. Simple experiments are proposed for measuring the vortex viscosity of suspensions in an unequivocal manner, essentially free of the question of internal spin boundary conditions. In dilute suspensions, first-order wall effects upon the translational and rotational motions of isolated spherical particles are employed to interpret the heretofore unexplained macroscopic “swirling” motions observed in ferrofluid suspensions when subjected to a circularly rotating magnetic field. In particular, it is shown inter alia that this swirling motion (relative to the fixed container walls) is a manifestation of the existence of a suspension-scale translational slip velocity occurring at the container walls, arising from a combination of wall and external field effects. This translational slip, which—being a wall effect—is relatively small, is in addition to a much larger suspension-scale rotational slip velocity, whose existence is virtually independent of wall effects.     

Preparation of highly concentrated aqueous hydroxyapatite suspensions for slip casting

This paper reports the preparation of highly concentrated aqueous hydroxyapatite (HA) suspensions for slip casting of dense bone implants. The dispersing behaviour of HA powders in aqueous media was monitored by viscosity and zeta potential analyses as a function of pH of the slurry. The rheological properties of concentrated aqueous hydroxyapatite suspensions have been characterized with varying pH, NH₄PAA concentration and solids loading. The intrinsic pH of the suspension was found suitable for slip casting. The optimum dispersant concentration is 0.75 wt.% for 75 wt.% solid loading. A stable suspension with 75 wt.% solid was suitable for slip casting with viscosity of 0.36 Pa s at 100 s⁻¹. Finally, crack-free and dense microstructures have been obtained successfully with a grain size of 2–5 μm.     

Mullite-zirconia composites: Effect of citric acid addition on slip and cast properties

Dispersion of mixed suspensions of zircon and α -alumina using citric acid as dispersant followed by pressure filtration produced after sintering (1600^∘C—2 h) dense mullite-zirconia composites. The effect of citric acid addition and pH on the rheological behavior of the mixed suspensions (57 vol%) was examined. Most of flow curves showed a shear thinning behavior at low shear rates reaching the viscosity a plateau at high shear rates. Newtonian viscosity at high shear rates values decreased to a minimum and then increased with increasing the amount of dispersant added. Compacts prepared from well stabilized suspensions achieved a maximum relative density of 72% (theoretical) which is slightly higher than that obtained from suspensions dispersed with a polyelectrolyte. Characteristics of sintered compacts such as density and crystalline phase composition by XRD were determined.     

The importance of hemoglobin contents on viscosity of liposome encapsulated hemoglobin suspensions

Abstract

The viscosities of pig hemoglobin solutions and liposome encapsulated pig hemoglobin (LEH) suspensions were systematically measured as a function of shear rates, temperature, hematocrits of LEH suspensions, concentrations of hemoglobin solutions and hemoglobin contents in LEH suspensions. Newtonian flow behavior of hemoglobin solution is observed. Moreover, the viscosity values of the solutions linearly decrease as the solution warms from 4°C to 37°C, but non‐linearly increase with an increase in the concentration of hemoglobin in solutions. In contrast to hemoglobin solutions, LEH suspensions show non‐Newtonian flow behavior at all tested shear rates. The viscosity values of LEH suspensions non‐linearly decrease as the solution warms from 4°C to 37°C, but increase with an increase of hematocrit and hemoglobin content of solutions. The above mentioned non‐linear flow behavior of LEH suspensions is strongly dependent on the hemoglobin contents in suspensions. Moreover, LEH suspensions with hemoglobin contents of 7.2 g/dl is Theologically the most suitable suspensions for further applications.     

ZTA陶瓷注凝成型浆料流变性能的研究

研究了ZTA陶瓷注凝成型浆料流变性能的影响因素.结果表明:单体(AM)在液相中质量百分浓度为10%、交联剂与单体的比(MBAM/AM)较低时,悬浮体粘度较低;浓悬浮体粘度和剪切应力随分散剂掺量增加而减小,拟合的流变模型倾向为Herchel Bulk;ZrO2原料的粒度对浆料流变性有重要影响,较粗ZrO2原料对浆料流变性影响不大,占少量的超细ZrO2决定了ZTA浓悬浮体的性质;试验条件下研磨时间以9h为最佳.     

短纤维悬浮体系的流变性质

本文介绍了Dinh-Armstrong流变本构方程,并由此导出了中等浓度纤维悬浮体的粘度、第一法向应力差、第二法向应力差以及拉伸粘度的解析表达式,在简单剪切流时,导出的解析式与Dinh-Armstrong方程的数值解是一致的.在拉伸流时,尽管起始时和稳定态的粘度一致,但在过渡阶段存在一些定量的差异.     

A continuum theory of rigid suspensions

A continuum theory of rigid suspension is presented. The theory modifies and extends the Batchelor^1,2 theory of fiber suspensions to heat conducting thermo-viscous Newtonian solvents carrying rigid suspensions.     

Injection of calcium phosphate pastes: prediction of injection force and comparison with experiments

Calcium phosphate ceramics suspensions (ICPCS) are used in bone and dental surgery as injectable bone substitutes. This ICPCS biomaterial associates biphasic calcium phosphate (BCP) granules with hydroxypropylmethylcellulose (HPMC) polymer. Different ICPCS were prepared and their rheological properties were evaluated in parallel disks geometry as a function of the BCP weight ratio (35, 40, 45 and 50?%). The suspensions show a strongly increased viscosity as compared to the suspending fluid and the high shear rate part of the flow curve can be fitted with a power law model (Ostwald-de Waele model). The fitting parameters depend on the composition of the suspension. A simple device has been used to characterize extrusion of the paste using a disposable syringe fitted with a needle. The injection pressure of four ICPCS formulations was studied under various conditions (needle length and radius and volumetric flow rate), yielding an important set of data. A theoretical approach based on the capillary flow of non-Newtonian fluids was used to predict the necessary pressure for injection, on the basis of flow curves and extrusion conditions. The extrusion pressure calculated from rheological data shows a quantitative agreement with the experimental one for model fluids (Newtonian and HPMC solution) but also for the suspension, when needles with sufficiently large diameters as compared to the size of particles, are used. Depletion and possibly wall slip is encountered in the suspensions when narrower diameters are used, so that the injection pressure is less than that anticipated. However a constant proportionality factor exists between theory and injection experiments. The approach developed in this study can be used to correlate the rheological parameters to the necessary pressure for injection and defines the pertinent experimental conditions to obtain a quantitative agreement between theory and experiments.     

直接凝固注模成型技术

直接凝固注模成型是瑞士苏黎世联邦高等工业学院L.J.Gauckler实验室发明的一项新的成型技术,具有素坯密度高、密度均匀、坯体收缩和形变极小等优点,特别适用于大尺寸、复杂形状的陶瓷部件的成型,有广阔的应用前景．本文着重介绍了直接凝固注模成型的基本原理和技术关键．     

A constitutive approach for studying concentrated suspensions of rigid fibers in a non ‐ Newtonian Ellis fluid

Abstract

A constitutive model for a semi‐concentrated suspension of rigid fibers in a non‐Newtonian fluid is derived in the present study. This work is extended from a previous work by Dinh and Armstrong which counted rigid fibers suspended in a Newtonian fluid. To investigate the effect of the shear‐dependent suspending fluid on the shear viscosity of suspension, the Ellis fluid is assumed to model such a non‐linear matrix. It is shown that the present derivation, via a cell model, gives an analytic form to calculate the drag coefficient of fibers and to illustrate the influence of material parameters of matrix fluid. The resulting equation gives the bulk stress in terms of an integral over a fourth‐order orientation vector, e, similar to the expression of Doi and Edwards for dense macromolecular fluid. For the purpose of evaluation, the present model attempts to predict the rheological behavior in the inception of flow, steady simple shear flow and stress‐growth experiments.     

流场中高分子共混物分散相的形态变化

评述了高分子共混物分散相微粒在流场中形变、破裂和凝聚的研究进展。     

Preventing ageing on Al2O3 casting slips dispersed with polyelectrolytes

Slip casting process needs a highly stabilized and well-characterized suspension, which involves not only the traditional rheological measurements, but an estimation of the colloidal stability in terms of interaction potentials between particles. For electrosterically stabilized ceramic suspensions the calculation of the steric contribution is not well described in the available theories because they are developed for ideal conditions where many variables affecting the stability of concentrated suspensions are neglected. In this work, alumina suspensions were prepared at 75 wt% solids and characterized considering the potential energy curves and the rheological behaviour. The main objective is to select the proper dispersing conditions in order to prevent ageing of the slips, which is an important problem in any manufacturing cycle. For the polyacrylate dispersant used it was shown that a concentration of 0.8 wt% provided the lowest viscosity, allowed ageing prevention and resulted in higher green and sintered densities.     

A new approach to the effective viscosity of suspensions

Study of the effective viscosity of suspensions is not only of interest in science, but also of great practical relevance to industries, such as the petrochemical industry, food and nutrition, materials processing and so on. In this paper, an attempt is made to establish theoretically the correlation between the effective viscosity of suspensions and their microstructural features. Firstly, the method for microstructural characterization developed by Fanet al. will be introduced to describe effectively the particle distribution in a suspension, and then the analogy between viscosity and field properties will be used to develop a new approach for the effective viscosity of suspensions. The new approach considers implicitly the effects of size, shape, orientation and distribution of the solid particles within the suspension through the topological parameters. Therefore, it can be applied to a suspension containing solid particles with any size, shape, orientation and distribution. Compared with other models available in the literature, the present approach is more realistic and more versatile. It can be applied to both liquids containing solid particles with a very high viscosity, and porous suspensions where the second phase has a vanishing viscosity. Perhaps more importantly, the present approach can predict the well-known S-shaped log-volume fraction curve in the whole range of microstructures (from completely continuous to completely discontinuous) and is in better agreement with experimental results.     

Water based gelcasting of lead zirconate titanate

Gelcasting is a novel forming method for making high-quality ceramic parts by means of in situ polymerization where only a few percents of a polymerizable binder are needed. In this article the viscosities of lead zirconate titanate (PZT) suspensions with 15-52 vol.% solids loading were studied. After developing a concentrated PZT suspension with a low viscosity, gelcasting was successfully used to form PZT ceramic parts. Microstructures and piezoelectric properties of gelcast samples derived from suspensions with different solids loading were also investigated in comparison with those of die pressed ones. It was found that gelcast samples exhibited slightly stronger piezoelectric effect than the die pressed ones at the same sintering procedure. Based on the comparison of the density and pore structure results of the samples prepared by these two methods, their different piezoelectricity may be attributed to their microstructure difference.     

Dependence of the Viscosity on the Concentration of Particles by the Example of Blood and Erythrocytic Suspensions

A model of the dependence of the relative viscosity of blood and suspensions of erythrocytes on their volume concentration is proposed. Both parameters of the model correlate differently with each other in three regions of erythrocyte concentrations (for man: Hct < 0.3, Hct = 0.3–0.7, Hct > 0.7). They change abruptly when going through the boundaries of the regions. It is suggested that one of them reflects the intensity of interaction of particles in a suspension and the other is related to the effective radius of hydrodynamic resistance. The model adequately describes the experimental data on the rheology of protein solutions and other suspensions.     

An Interpretation of the Sedimentation Behavior of Pharmaceutical Kaolin and Other Kaolin Preparations in Aqueous Environments

Abstract

The effect of flocculant materials on kaolin-water suspensions is reported using two kaolins. One of these is a pharmaceutical-grade kaolin and the other an industrial kaolin. These two systems serve as a model in a broader investigation which will systematically study the ancillary ingredients of pharmaceutical kaolin-based suspensions. These studies are based on concentrated suspensions where fall of particles is hindered and characterized by sedimentation “en bloc” with a sludge line serving as interface between the supernatent liquid and the settling suspension. It is shown that there is an optimum concentration of macromolecular flocculant which causes maximum flocculation. At higher concentrations of flocculant the system is stabilized. Two approaches are used to explain the results. The first represents the phenomenon as a modification of Stokes Law results. A correlation is found between the parameter A used as a characterization constant in Steinour's empirical relationship and the Richardson and Zaki exponent n. A theoretical justification of this relationship is provided. A permeability relationship is used in the second approach based on the application of permeability equations put forward by Kozeny-Carmen. The variable k in the resultant equation is shown in theory and in practice to have a minimum at some value of porosity determined by the nature of the concentrated suspension. This treatment is applied here to flocculated systems. The systems are found in general to show very high hindrance     

Determination of phenomenological constants of shear-induced particle migration model

Particles in initially well-mixed suspensions subject to inhomogeneous shear flows will migrate and establish a particle concentration gradient and a non-Newtonian velocity profile. In this study, a phenomenological diffusive flux model coupled with flow equations was employed to describe the shear-induced particle migration in a concentrated suspension. The focus of the paper is on the determination of the two phenomenological constants in the diffusive flux model k_c and k_η. They were determined inversely by employing a least square analysis on the experimental pressure data with different capillary die ratios of length to diameter of the die. The pressures and the flow patterns of the non-Newtonian concentrated suspension were predicted in terms of these two phenomenological constants. The results indicated that particle migration should be accounted for to properly characterize the rheological behaviour of concentrated suspensions.