共查询到20条相似文献,搜索用时 433 毫秒
1.
Hiroshi Kimura Mikito Sakurai Taiki Sugiyama Akira Tsuchida Tsuneo Okubo Toru Masuko 《Rheologica Acta》2011,50(2):159-168
The relationship between the rheological properties of deionized aqueous suspensions of hectorite particles and the dispersion
states of the particles has been studied with a broad range of salt and particle concentrations. The shear viscosity of the
hectorite suspensions decreases drastically after exhaustively deionizing the suspensions with ion-exchange resins. By means
of DLS measurements, it is clarified that the average size of the flocs of hectorite particles decreases and reaches the Stokes
diameter of the individual particle as the degree of deionization advances. This fact strongly supports the idea that the
electrical double layer around the hectorite particles expands significantly in the exhaustively deionized state and the particles
are well-dispersed individually and do not form a three-dimensional network structure composed of particles, whereas such
a network structure forms in the presence of a large amount of salt. In the case of exhaustively deionized state, the suspension
forms a glassy state, at high particle fractions. The results show the importance of the electrical double layer that causes
a strong repulsive force among the particles on the particle dispersion state, especially in the exhaustive deionization area
below 10 − 4 M, and on the rheological properties; the hectorite suspension can be considered a Newtonian liquid in the deionized state,
but it becomes elastic-solid in the presence of salt above a certain concentration confirmed by normal stress measurements. 相似文献
2.
《ournal of non Newtonian Fluid Mechanics》1998,81(3):235-250
We have investigated the electrorheological properties of dispersions of semi-conducting particles in oils and elastomers. We focused on how the dynamic mechanical properties measured under oscillatory shearing change with the viscosity of the oil or the elasticity of the elastomer. The dependence on electric field and strain amplitude were also investigated. We found that the largest increment of the mechanical properties under electric fields was obtained when using oils of low viscosity and elastomers of low elasticity. The strain amplitude which produced the largest variation with electric field was found to be 0.1% for the elastomer systems, but significantly larger (1%) for the oil systems. These results are interpreted in terms of a model based on the competition between the dipole–dipole electrostatic interaction (which acts to maintain neighbouring particles together) and the shearing force due to the deformation of the matrix (which acts to separate the particles). We find that there are parallels between the electrorheological behaviour of particles dispersed in elastomers and the behaviour of particles dispersed in oils. These results should find application in the selection of suitable matrix materials for electrorheological suspensions. 相似文献
3.
Electrorheological (ER) fluids composed of iron(III) oxide (hematite) particles suspended in silicone oil are studied in this work. The rheological response has been characterized as a function of field strength, shear rate and volume fraction. The dielectric properties of the suspensions were first studied in order to get information about the conductivity of the solid. Rheological tests under a.c. electric fields elucidated the influence of the electric field strength and volume fraction on the field-dependent yield stress. It was found that this quantity scales as a square power law in both cases. The viscosities of electrified suspensions were found to increase by several orders of magnitude as compared to the unelectrified suspension at low shear rates, although at high shear rates hydrodynamic effects become dominant and no effects of the electric field on the viscosity are observed. The ER behaviour of the suspensions was analysed by considering the fundamental forces (of hydrodynamic and electrostatic origin) acting on the particles and it is found that, at a given volume fraction, all the dependencies of relative viscosity on shear rate and field strength can be described by a single function of the Mason number, Mn. Finally, two different chain models were used to explain the shear-thinning behaviour observed: rheological measurements showed a power-law dependence of relative viscosity decrease on the Mason number, F~Mn, with –0.95. 相似文献
4.
Suspensions of polydimethylsiloxane (PDMS) containing low amounts (1 wt.% or less) of a highly conducting carbon black (CB)
filler are rendered conductive and exhibit electrorheological (ER) responses under shear flow when exposed to an externally
applied AC electric field. The presence of columnar structures, consisting of CB particles aligned in the direction of the
electric field is evidenced through optical microscopy experiments. The appearance of yielding behavior and positive ER response,
manifested by an increase in the viscosity of the suspensions, depend strongly on the filler loading, strength of the electric
field, magnitude of the shear field, and viscosity of the medium. The responses are stronger at low filler loadings, below
the percolation threshold, and at very low shear rates, where the microstructure of the dispersed phase remains intact. At
higher shear rates, corresponding to Mason numbers (Mn) above 1, the structure is disrupted and thus does not contribute to
the observed shear stress. The rheological characterization is accompanied with admittance measurements, to demonstrate that
the induced polarization forces between particles lead to the formation of electrically conductive structures within the polymer
matrix. A critical comparison with the qualitative predictions based on the theory of induced dipole–dipole interactions shows
that the theory is valid for these dilute systems. 相似文献
5.
Controlled rotation of a suspended soap water film, simply generated by applying an electric field, has been reported recently.
The film rotates when the applied electric field exceeds a certain threshold. In this study, we investigate the phenomenon
in films made of a number of other liquids with various physical and chemical properties. Our measurements show that the intrinsic
electrical dipole moments of the liquid molecules seems to be vital for the corresponding film rotation. All the investigated
rotating liquids have a molecular electric dipole moment of above 1 Debye, while weakly polar liquids do not rotate. However,
the liquids investigated here cover a wide range of physical parameters (e.g. viscosity, density, conductivity, etc.). So
far, no significant correlation has been observed between the electric field thresholds and macroscopic properties of the
liquids. 相似文献
6.
《ournal of non Newtonian Fluid Mechanics》2005,125(1):1-10
Electrorheological (ER) fluids composed of α-Fe2O3 (hematite) particles suspended in silicone oil are studied in this work. The rheological response has been characterized as a function of field strength, shear rate and volume fraction. Rheological tests under DC electric fields elucidated the influence of the electric field strength, E, and volume fraction, ϕ, on the field-dependent yield stress, τy. It was found that this quantity scales with E and ϕ with a linear and parabolic dependence, respectively. The viscosities of electrified suspensions were found to increase by several orders of magnitude as compared to the unelectrified suspension at low shear rates, although at high-shear rates hydrodynamic effects become dominant and no effects of the electric field on the viscosity are observed. The work is completed with the analysis of microscopic observations of the structure acquired by the ER fluid upon application of a constant electric field. Electrohydrodynamic convection is found to be the origin of the ER response rather than the commonly admitted particle fibrillation. This fact can provide an explanation to the relationship between yield stress and electric field strength as well as the pattern of periodic structures observed in the measurement geometries. 相似文献
7.
IntroductionAnelectrorheologicalfluid (ER)consistsofasuspensionofthedielectricparticlesinaliquidoflowdielectricconstantandlowviscosity .Itsapparentviscosityincreasesdramaticallyinthepresenceofanappliedelectricfield .Thephenomenonisreversible.Uponelectric… 相似文献
8.
用 HAAKE RV2 0型流变仪 ,在不同外加电场强度和不同颗粒体积分数下测试了基于沸石和硅油的电流变液的剪切应力变化 .结果表明 :随着外加电场强度升高 ,电流变液的零电场粘度急剧增加 ,电流变液的剪切屈服应力增加 ;随着电流变液中沸石颗粒体积分数升高 ,电流变液的剪切屈服强度急剧上升 .这种变化可以用颗粒间作用力与颗粒间距的关系、单位面积的颗粒链数目变化以及多体作用对电流变液性能的影响来解释 相似文献
9.
以微观试验和流变性能试验为手段,分别研究零电场下和在电场作用下的电流变液体黏性变化规律.研究结果表明:零电场下电流变液体的黏性与Krieger-Dougherty公式具有很好的拟合效果,其中逾渗临界值强依赖于悬浮液体中固体颗粒的性质并随工作温度变化.在电场作用下,电流变悬浮液体的黏度随剪切速率的变化规律分为3个阶段:即呈线性的启动段、非线性的幂定律模型流动段和宾汉模型流动段.研究结果为电流变效应工程应用提供依据. 相似文献
10.
Modesto T. López-López Pavel Kuzhir Georges Bossis Pavel Mingalyov 《Rheologica Acta》2008,47(7):787-796
In this work, we describe methods for the preparation of suspensions of micron-sized iron particles grafted with different
surfactants. The aim is to obtain well-dispersed magnetorheological (MR) fluids. The effectiveness of the surfactants as dispersants
was analyzed quantitatively by means of rheological measurements. With this objective, the viscosity of the suspensions was
measured, and the results were compared with the prediction of the Batchelor’s formula (Batchelor, J Fluid Mech 83:97–117, 1977). The effect of dispersion on the MR properties of the suspensions was also studied. It was found that the
quality of the dispersion of a suspension does not have an important effect on the magnitude of the field-induced yield stress
but does on the change of viscosity induced by the field. It was also found that the transition from the solid-like state
to the liquid-like one happens very smoothly for well-dispersed suspensions, contrarily to the abrupt transition for poorly
dispersed suspensions. 相似文献
11.
E. V. Korobko Prof. V. E. Dreval Z. P. Shulman V. G. Kulichikhin 《Rheologica Acta》1994,33(2):117-124
Studies have been made of concentrated (up to 60%) diatomite suspensions in transformer oil, the structure and theological properties of which depend on an applied electric field. Studies have been conducted of steady-state and transient regimes of straining involving continuous and periodic shear. The structure in such suspensions is formed in the presence of an electric field of 10–3 –102 duration. The suspensions under continuous stationary strain behave as non-Newtonian fluids with a yield stress dependent on electric intensity. Under periodic deformation conditions the test suspensions exhibit elasticity which abruptly diminishes with increasing deformation amplitude. 相似文献
12.
Knowledge of the viscosity of concentrated suspensions is required for several technical applications, e.g. process control
in mechanical engineering, casting of ceramics and pipeline transport of solids. Our previous viscometric investigations of
concentrated suspensions showed, under particular shear conditions, an apparent viscosity that was periodic in time for a
constant shear rate and temperature. These results were obtained with rotational viscometers with a set coaxial geometry.
The inner cylinder was rigidly coupled to the viscometer driving axis. In this paper we describe a viscosity time behavior
which was found using another type of coupling. Measurements were performed with rotational viscometers with a non-rigidly
linked inner cylinder (small sample adapter supplied by Brookfield). Using kaolin suspensions of 30% solid mass content, viscosity
oscillations appear. They show a regular time pattern at certain intervals of low shear rates. The amplitudes reach up to
20% of the viscosity mean value. In addition a motion of the inner cylinder away from the coaxial position is observed. This
dislocation is followed by a relocation into the coaxial position. A maximum in the viscosity value is correlated with a maximum
of the dislocation position. The process of dislocation and relocation of the inner cylinder is assumed to be caused by local
anisotropically distributed inhomogeneities, which originate from shear-induced agglomeration and deglomeration of suspended
particles. The motion of the inner cylinder is described by introducing a perturbation term into the equation of motion. The
parameters of the perturbation term are fitted to the experimental data.
Received: 10 September 1998 Accepted: 28 April 1999 相似文献
13.
Multimodal suspensions, consisting of non-colloidal spherical particles and a Newtonian matrix, are considered. A new differential
(or multi-scale mean field approach) model for the relative viscosity of multimodal suspensions has been developed. The problem
of the random close packing fraction of the solid phase is also investigated. We suppose that the multimodal suspension has
a dominant large particle composition and that the smaller particles are embedded in the empty space between the larger particles.
The relative viscosity model can therefore be based on the theory of monomodal suspensions. Experimental data of Eveson are
compared to the predictions given by using three different models of monomodal suspensions respectively. The Maron–Pierce
approach appears to give the best agreement with Eveson’s experiments. However, due to experimental uncertainties, we recommend
that the Mendoza and Santamaria-Holek (MSH) formula be adopted. 相似文献
14.
考察了水对甲壳胺和甲壳胺-Cu^2 复合物/蓖麻油电流变体系的剪切应力或表观剪切应力及漏电流密度的影响。结果表明:随着水含量的增加,蓖麻油电流变体系的剪切应力增加,未出现饱和现象;当水含量约为颗粒含量的12.5%,漏电流密度出现一个突增拐点;水在甲壳胺类高分子聚电解质/蓖麻油电流变液中的作用机理与电流变液组分的化学结构及水的含量密切相关。 相似文献
15.
16.
17.
Ali Abdollahi Mohammad Hossein Karimi Darvanjooghi Arash Karimipour Mohammad Reza Safaei 《Meccanica》2018,53(15):3739-3757
In this study, the impacts of temperature, nanoparticles mass fraction, and basefluid types were investigated on the dynamic viscosity of CuO-loaded nanofluids. The nanoparticles were dispersed in deionized water, ethanol, and ethylene glycol as basefluids separately and the measurements were performed on samples with nanoparticles loads ranging from 0.005 to 5 wt%, and the temperature range of 25 to 70 °C. TEM analysis were performed on dried nanoparticles and the results showed the average mean diameter of CuO nanoparticles ranged from 10 to 50 nm. The results of DLS analysis confirmed the results of nanoparticles size obtained by TEM analysis in mentioned basefluids and Zeta-Potential tests exhibited the high stability of the nanoparticles in the basefluids environment. The results indicate that by adding tiny amount of CuO nanoparticles to basefluids, relative viscosity of nanofluid increases. By the increase in nanoparticles load higher than 0.1 wt% the effect of both nanoparticles mass fraction and temperature would be more tangible, while for nanoparticles mass fraction lower than 0.1 wt% no significant change in viscosity was observed. In addition, the results declare that viscosity of nanofluid remains constant at various applied shear rates indicating Newtonian behavior of nanofluid at various nanoparticles load and temperature. According to experimental data, it is also evident that with the increase in temperature, the value of relative dynamic viscosity decreases significantly. Also it is concluded that for CuO/ethanol nanofluid, more interfacial interaction is resulted that causes higher relative dynamic viscosity while for CuO/water lower interfacial interaction between nanoparticles surface and water molecules are resulted which leads to the lower values for this parameter. The results of this study implied that with increase the temperature from 25 to 70 °C at the condition where nanoparticles mass fraction was chosen to be 5 wt%, the value of dynamic viscosity of CuO/ethanol, CuO/deionized water, CuO/ethylene glycol declined 69%, 66%, and 65% respectively. Finally, a correlation was proposed for the relative dynamic viscosity of nanofluid based on the CuO nanoparticles mass fraction and temperature of the basefluid and nanoparticles. 相似文献
18.
This study presents the results from the rheological measurement of clay suspensions using vane geometry in a wide gap configuration. It focuses on how measurement of viscosity cannot be effective for two reasons: the limits of the vane geometry itself and the limits of the material depending on its content of solid particles. Image analysis of the flow while shearing the material is carried out to relate the flow behavior. Several approaches to compute the shear flow curve from torque-rotational velocity data are used. The results demonstrate that the applied setpoint while applying a logarithmic shear rate ramp can be very different from the calculated shear rate from existing theories. Depending on the solid volume fraction of the particles in the mixture, we relate the macroscopic behavior using image analysis and the shear flow curves to the rheophysical regime of the flow of the suspensions. Therefore, this paper has two simultaneous goals: the first one is to describe the physical phenomena which control macroscopic behavior and the second one is to highlight the limits of the vane geometry for viscosity measurement of mineral suspensions like kaolinite pastes. 相似文献
19.
范西俊 《应用数学和力学(英文版)》1987,8(9):829-838
The diffusion equation for the configurational distribution function of Hookean dumbbell suspensions with the hydrodynamic interaction (HI) was solved, in terms of Galerkin’s method, in steady state shear flow; and viscosity,first and second normal-stress coefficients and molecular stretching were then calculated. The results indicate that the HI included in a microscopic model of molecules gives rise to a significant effect on the macroscopic properties of Hookean dumbbell suspensions. For example, the viscosity and the first normal stress coefficient, decreasing as shear rate increases, are no longer constant; the second normal-stress coefficient, being negative with small absolute value and shear-rate dependent, is no longer zero; and an additional stretching of dumbbells is yielded by the HI. The viscosity function and the first normal-stress coefficient calculated from this method are in agreement with those predicted from the self-consistent average method qualitatively, while the negative second normal-stress coefficient from the former seems to be more reasonable than the positive one from the latter. 相似文献
20.
Suspensions of small nonspherical particles having dipolar moments exhibit non-Newtonian behavior under the influence of shear and external fields. Numerical methods are presented for calculating the rheological and rheo-optical properties of dilute suspensions of Brownian particles having permanent dipoles subject to time-dependent shear and external fields. The numerical methods employ the Galerkin method of weighted residuals to solve the differential equation for the particle orientation distribution function. The steady-state shear flow intrinsic viscosity of suspensions of particles with sufficiently extreme aspect ratio is predicted to exhibit a maximum value attained for intermediate shear rates at selected field orientations. These numerical results provide valuable insight into the coupling which occurs between the effects of rotary Brownian motion, the hydrodynamic resistance of nonspherical particles, and the external torque exerted on dipolar particles. The results are applicable to both suspensions of magnetic particles and electrically dipolar particles. 相似文献