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1.
A low-cost electrorheological (ER) material made of micro/nano-structured montmorillonite/titania particles was prepared by
a one-pot solvothermal method. The micro/nano-structured particles were characterized by X-ray diffraction, Fourier transform
infrared spectra, and scanning electron microscopy. It was found that the nanorod-like titania assembled on the surface of
montmorillonite, the diameters of the nanorods were about 30 nm, and the lengths were about 300 nm. The electrorheological
property of the micro/nano-structured particles in silicone oil was measured under dc electric fields. It was found that the
micro/nano-structured montmorillonite/titania ER fluid exhibited much stronger electrorheological effect compared to pure
montmorillonite and pure titania nanorod ER fluids, while its leaking current density was significantly lower than that of
montmorillonite ER fluid. The stronger electrorheological effect might be attributed to the larger interfacial polarization
and interparticle friction, which originated from the unique structure and morphology of micro/nano-structured particles,
compared to pure montmorillonite and pure titania nanorods. 相似文献
2.
Yongsok Seo 《ournal of non Newtonian Fluid Mechanics》2011,166(3-4):241-243
A new scaling function capable of modeling the yield stress behavior of electrorheological (ER) fluids through the full range of electric fields is proposed. In spite of its simple form, a comparison of the model predictions with experimental data for both ac and dc fields and the polarization model shows that the proposed model correctly predicts the yield stress behavior both quantitatively as well as qualitatively. 相似文献
3.
4.
Dielectric behaviors of titanium dioxide (TiO2)-based electrorheological (ER) suspensions with different particle concentrations and TiO2 polymorphs were investigated in the frequency range of 40 Hz to 110 MHz. Two relaxations in kilohertz and megahertz frequency range were attributed to interface polarization between TiO2 and silicone oil and ion pair polarization between dissociated counterions and fixed charges on TiO2 surfaces, respectively. Dipolar coefficient D, which is related to the construction or structure of the colloid, changes after critical volume fraction $\phi _{\rm c} \approx $ 0.05, indicating that chain-like or network structures are formed by particles. Based on percolation model, the values of critical exponent suggest that particles may form two-dimensional percolation network. Furthermore, the effective dielectric mismatch parameter, $\beta _{\rm eff}$ , was calculated based on the obtained phase parameters. We found that rutile should have better ER activity than anatase. The main reason for weak ER activity of pure TiO2 ER suspensions may due to poor conductivity properties of TiO2 crystals. 相似文献
5.
An electrorheological (ER) response is defined as the dramatic change in rheological properties of a suspension of small particles
due to the application of a large electric field transverse to the direction of flow. ER fluids are typically composed of
nonconducting or semiconducting particles dispersed in a nonconducting continuous phase. A sufficiently large electric field
will cause ER fluids to solidify, giving rising to a yield stress. Many applications in torque and stress transfer devices
were proposed employing the reversible yielding behavior of ER fluids. Successful applications depend on a large yield stress
of ER fluids and therefore accurate measurements of the yield stress of ER fluids are required. Reported experimental yield
stresses of ER fluids have been dynamic yield stresses obtained by extrapolating the shear stress–shear rate data to zero-shear
rate. It would be very helpful to the understanding of ER behaviors and the applications of ER fluids to be able to measure
the static yield stress of ER fluids accurately. The slotted plate technique has been shown to be a successful method to determine
the static yield stress of suspensions. The values obtained via the slotted plate method are static yield stress as the platform
is designed for extremely low-speed motion. In this study, we modified the slotted plate device for the application of large
electric fields and measured the static yield stress of TiO2 ER fluids under various electric fields. The measured static yield stress values are also compared with the static yield
stress values from a commercial rheometer. 相似文献
6.
The electrorheological response of elongated particles 总被引:1,自引:0,他引:1
7.
The yield stress of polymethylmethacrylate (PMMA) composites filled with ultrafine SiO2 particles was measured as a function of the draw temperature, rate of strain and filler content. The yield stress of the composites increased with increasing filler content and decreasing filler size. The tensile yield stress was found to be reducible with regard to draw temperature, rate of strain and filler content. At a given filler content, a master curve was obtained for the yield stress plotted versus the logarithm of the strain rate. The Arrhenius plot of the shift factors (a
T
) used to produce the strain rate-temperature master curve formed a single curve for all sizes and loadings of the filler. The master curves obtained for different loadings of a filler of given size could be further reduced into a master-master curve by shifting them along the axis of strain rate, with the logarithm of the second shift factors (loga
c
) proportional to the 4/5th power of the filler volume fraction (V
f
). The proportionality constant and the exponent represent the extent of the filler reinforcing effect in the polymer. These values were found to be correlated with the critical surface tension of the polymers. 相似文献
8.
This paper presents results on the rheological behaviour of suspensions of two kinds of TiO2 particles in two different polymer solutions. The particles differ in their hydrophilic or hydrophobic properties. The dispersing
media are a solution of high molecular weight polyisobutylene in decalin and a solution of a low molecular weight polybutene
in decalin. The concentrations of polymer are adjusted in order to get the same zero shear viscosity. The shear viscosity
measurements display an apparent yield stress in some cases. The existence and the values of the yield stress depend on the
volume fraction of solid particles and on the type of particles. The evolution of the intrinsic viscosity and of the maximum
packing fraction vs the shear rate is interpreted in terms of evolution of the size and of the shape of aggregates of particles
under shear. The effect of temperature on the development of the yield stress is also discussed. The results are completed
by microscopic observations. 相似文献
9.
Chao Hu Xueqian Fang Wenhu Huang 《Archive of Applied Mechanics (Ingenieur Archiv)》2008,78(3):177-190
A new approach is proposed to investigate the propagation of a plane compressional wave in matrix composite materials with
high volume concentrations of particles. The theory of quasicrystalline approximation and Waterman’s T matrix formalism are employed to treat the multiple scattering resulting from the particles in composites. The addition theorem
for spherical Bessel functions is used to accomplish the translation between different coordinate systems. The Percus–Yevick
correlation function widely applied in the molecular theory of liquids is employed to analyze the interaction of the densely
distributed particles. The analytical expression for the Percus–Yevick correlation function is also given. The closed form
solution for the effective propagation constant is obtained in the low frequency limit. Only numerical solutions are obtained
at higher frequencies. Numerical examples show that the phase velocities in the composite materials with low volume concentration
are in good agreement with those in previous literatures. The effects of the incident wave number, the volume fraction and
the material properties of the particles and matrix on the phase velocity are also examined. 相似文献
10.
《ournal of non Newtonian Fluid Mechanics》2005,129(3):177-181
A modified Herschel–Bulkley model [E. Mitsoulis, S.S. Abdali, Flow simulation of Herschel–Bulkley fluids through extrusion dies, Can. J. Chem. Eng. 71 (1993) 147–160] predicts an infinite apparent viscosity at vanishing shear rate. Furthermore, the dimensions of one parameter depend on another parameter. In this contribution, we propose a generalized model based on earlier work by De Kee and Turcotte [D. De Kee, G. Turcotte, Viscosity of biomaterials. Chem. Eng. Commun. 6 (1980) 273–282] and on the work of Papanastasiou [T.C. Papanastasiou, Flows of materials with yield, J. Rheol. 31 (1987) 385–404] to solve the problems associated with the modified Herschel–Bulkley model. Compared to the responses of the Papanastasiou model and the modified Herschel–Bulkley model, the proposed generalized model provides the expected improvements and is capable of predicting successfully the rheological behavior (viscosity and yield stress) of Carbopol 980 dispersions. 相似文献
11.
12.
Illinois coal was ground and wet-sieved to prepare three powder stocks whose particle-size distributions were characterized. Three suspending fluids were used (glycerin, bromonaphthalene, Aroclor), with viscosities
s that differed by a factor of 100 and with very different chemistries, but whose densities matched that of the coal. Suspensions were prepared under vacuum, with coal volume fractions that ranged up to 0.46. Viscosities were measured in a cone-and-plate over a shear rate
range 10–3–102 s–1. Reduced viscosity
r = /s is correlated in the high-shear limit (
) with/
M, where
M is the maximum packing fraction for the high-shear microstructure, to reveal the roles of size distribution and suspending fluid character. A new model that invokes the stress-dependence of
M is found to correlate
r well under non-Newtonian conditions with simultaneous prediction of yield stress at sufficiently high; a critical result is that stress and not
governs the microstructure and rheology. Numerous experimental anomalies provide insight into suspension behavior. 相似文献
13.
14.
Baoliang Zhang Qiuyu Zhang Hepeng Zhang Xinlong Fan Dezhong Yin Xiangjie Li Wei Li 《Particuology》2013,11(5):574-580
This paper describes a novel chemical method for preparing SiO2/TiO2 Janus particles. First, polystyrene (PSt)/SiO2 particles with a raspberry-like structure are prepared by electrostatic assembly. The influences of the reaction time of sulfonation and the treatment times of polyelectrolyte solutions (PDADMAC, PSS) on PSt and SiO2 are investigated with respect to the surface charge density of the particles. SiO2/TiO2 Janus particles are then obtained by hydrolysis of butyl titanate on the surface of PSt/SiO2 particles followed by a calcination process. Particle size analyzer, Zeta potential instrument, FTIR, TEM and SEM are used to characterize the particle size, the amount of charge on the surface of PSt and SiO2 particles and the compositions and morphologies of PSt/SiO2, SiO2/TiO2 and PSt/SiO2/TiO2. The diameters of the PSt, SiO2, PSt/SiO2 and SiO2/TiO2 particles are 2.0 μm, 303 nm, 2.7 μm and 330 nm, respectively. 相似文献
15.
G. P. De Loor 《Applied Scientific Research》1965,11(1):310-320
Summary After defining the boundaries for the dielectric constant of a heterogeneous mixture, the behaviour of such a mixture is studied as a function of the frequency, when one of its components is polar. Deviations from a semicircle are to be expected for the function
m
=f(
m
) even when the dielectric properties of the polar constituent can be described with a semicircular Cole-Cole-arc. The relaxation time of the mixture is shorter than that of the polar constituent. 相似文献
16.
《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
17.
?????????Mohr-Coulomb??????????????? 总被引:2,自引:0,他引:2
在应用Mohr-Coulomb屈服条件时,由于中主应力不影响判别材料是否进入屈服,因此有关中主应力对Mohr-Coulomb材料屈服的影响性质关注较少.考虑Mohr-Coulomb屈服条件与应力路径相关性,本文采用Lode角或Lode数描述了偏平面上屈服性质的分区,对任意满足Mohr-coulomb屈服条件的应力状态,在保持其大、小主应力不变的条件下给出了中主应力在大、小主应力之间变化时的屈服轨迹,从而明确了中主应力对Mohr-Coulomb材料屈服性质的影响. 相似文献
18.
The methods normally employed for shear rate calculations from concentric cylinder viscometer data generally are not applicable for fluids with a yield stress. In cylindrical systems with large radius ratios, as usually is the case with suspensions, the yield stress induces two possible flow regimes in the annulus. Unless the yield value is exceeded everywhere in the gap only part of the fluid can be sheared while the remaining region behaves like a solid plug. A correct calculation of the shear rate must take into account the presence of a variable effective gap width determined by the extent of the sheared layer. For time-independent yield stress fluids, a two-step procedure, which does not require any specific flow model, is proposed for analysing the experimental torque-speed data. Under the partially sheared condition, the shear rate can be computed exactly, whereas for the fully sheared flow the Krieger and Elrod approximation is satisfactory. The method is assessed by examining both semi-ideal data generated with a Casson fluid with known properties, and experimental data with an industrial suspension. A more complicated problem associated with characterization of time-dependent yield stress fluids is also identified and discussed. An approximate procedure is used to illustrate the dependence of the shear rate on time of shear in constant-speed experiments. 相似文献
19.
The impact of a yield stress fluid drop onto a solid surface with diversified interface properties has been experimentally
investigated. Two smooth substrates with distinct surface energies and three similar substrates with different roughnesses
have been used. The bulk shear rheological behaviour of Carbopol gels, concentrated suspensions of swollen micro-gels, has
been measured. Wall friction has also been characterized on each substrate. Slip effects of gels proved to be greater on a
more hydrophobic substrate. They decreased with an increase in roughness. The drop hydrodynamics during the impact was correlated
with the wall friction of the gels on all substrates and with the ratio of surface roughness to size of the swollen micro-gels.
At very low impact velocities, the gravitational subsidence amplitude depends greatly on surface properties. At higher impact
velocities, no significant difference is observed during the spreading phase. The drop behaviour differs during the retraction
depending on the substrate. Interface effects during the retraction stage proved to diminish when the yield stress value increases. 相似文献
20.
《Particuology》2023
With the outbreak of COVID-19, disinfection protection has become a necessary measure to prevent infection. As a new type of disinfectant, potassium peroxymonosulfate compound salt (PMS) has the advantages of good bactericidal effect, non-toxicity, high safety and stability. However, the current PMS products with irregular particle shapes lead to poor flowability, high hygroscopicity, poor stability of reactive oxygen species (ROS) and serious caking problems. In this work, an agglomeration-dissolution mechanism was designed to prepare spherical PMS particles with large size (>300 μm) and high sphericity (up to 90%), effectively addressing the above problems. Shaping (dissolution and abrasion) is the key to improving sphericity, which is mainly controlled by the design of the heating mode, residence time and stirring rate. Compared with the irregular PMS particles, the large spherical particles present better flowability (angle of repose decreased by 35.80%, Carr's index decreased by 64.29%, Hausner's ratio decreased by 19.14%), lower hygroscopicity (decreased by 38.0%), lower caking ratio (decreased by 84.50%), and higher stability (the monthly loss of ROS was reduced by 61.68%). The agglomeration-dissolution mechanism demonstrates the crystallization, agglomeration, dissolution and abrasion process of inorganic salt crystals, providing an opportunity to prepare high-end inorganic crystal materials with high-quality morphologies. 相似文献