Characteristics and mechanisms of electrorheological fluids

Conrad, H.; Sprecher, A.F.

doi:10.1007/bf01048815

Cited by 74 publications

(35 citation statements)

References 15 publications

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“…Uejima (1972) reported s y µ E 2 for cellulose fluids while for starch-based systems Chen and Conrad (1993) reported s y µ E n where n varied from 2 (no water) to 1.5 (water content range: 4-10%) and ultimately decreased to near 0 above 10% water content. The most common value of n in ER systems is 2, which is consistent with the polarization theory (Klingenberg and Zukoski 1990;Conrad and Sprecher 1991;Davis 1992;Hao et al 1998). Deviations from n = 2 cannot be explained by this theory.…”

Section: As Illustrated Insupporting

confidence: 62%

“…Wen et al (1997) studied the dependence of ER activity on water content in AC electric fields and concluded that water was significantly influencing the dielectric constants of fluids. Other mechanisms for the ER effect were given by Winslow (1949), Klass and Martinek (1967a, b), Klingenberg and Zukoski (1990), Conrad and Sprecher (1991), Davis (1992), and Hao et al (1998). Despite these efforts, no single model can explain all the steady and dynamic physical properties of ERFs.…”

Section: Introductionmentioning

confidence: 96%

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Water-activated cellulose-based electrorheological fluids

2005

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The performance of electrorheological (ER) fluids containing cellulose particles dispersed in lubricating oil was investigated as a function of particle water content, DC electric field strength, particle concentration, and temperature. Over a range of applied electric fields (0-3 kV/mm), yield stress was observed to increase with increasing cellulose moisture content up to 8.5 wt% followed by a decrease. Water adsorbed by cellulose particles used in these systems was shown to be non-freezing bound water. The maximum ER response for a cellulose-based fluid at 25°C was observed at a moisture content near the transition of less mobile 'liquid-like' (LM) water to more mobile 'liquid-like' (MM) non-freezing water. At a constant moisture level, yield stress increased linearly with increases in either electrical field strength or particle concentration, while the ER effect decreased with increasing temperature. The present study concludes that the performance of water-activated ER fluids based on cellulose particles is influenced strongly by the mobility of non-freezing bound water adsorbed onto cellulose.

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Section: As Illustrated Insupporting

confidence: 62%

Section: Introductionmentioning

confidence: 96%

Water-activated cellulose-based electrorheological fluids

2005

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“…[39] However, other studies also reported that the a value was experimentally between 1 and 2.5 depending on the magnitude or range of the electric field and the nature of the particles. [40][41][42] In this study, the deviation from 2.0 might be due to the structural inhomogenity of the SAN particles as well as the high electric field range. The AN component is thought to exist mainly at the outer phase of particles during the seeded polymerization because of its hydrophilic characteristics, and this tendency will be intensified at higher AN concentration.…”

Section: Particle Characteristicsmentioning

confidence: 99%

Preparation and Electrorheological Characterization of Suspensions of Monodisperse Micron‐Sized Styrene–Acrylonitrile Copolymer Particles

Jun

Uhm

Suh

2003

Macro Chemistry & Physics

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IntroductionThe electrorheological (ER) effect of fluids, first reported by Winslow [1] in 1949, has been extensively studied for the past two decades and reviewed in several publications. [2][3][4][5][6] Typical ER fluids are suspensions that consist of polarizable solid particles dispersed in a nonconducting medium. When an external electric field of several kV/mm À1 is applied on this system, the immediately polarized suspension particles orient along the electric field direction and connect themselves into chains or columns spanning the gap between the two opposite electrodes. This change in the suspension structure strongly affects the rheological properties of the fluid. On the other hand, the viscosity of the fluids recovers the original state promptly by removing the applied field. This switching ability of ER fluids by electric field, together with the rapidity of the structural and rheological interconversion, renders them not only of academic interest but also of practical importance with potential applications, including electrical clutches, locks, valves, shock absorbers, sensors, tactile displays and so on.Many researchers investigated extensively a variety of dispersions for ER effect. Most of the ER suspensions reported in early period were water-activated systems, in which water or some other polar activator is originally considered necessary for the ER effect. Thus, the hydrous ER fluids possess their own various weak points, especially a limited operating temperature due to the loss of adsorbed Full Paper: Monodisperse micron-sized styrene-acrylonitrile copolymer (SAN) particles were prepared by a seeded swelling and polymerization method. Polystyrene particles prepared by dispersion polymerization were used as the seed latex. Characteristics of the particles were examined by scanning electron microscopy, FT-IR spectroscopy, 1 H NMR spectroscopy, thermogravimetric analysis and dielectric analysis, then the electrorheological (ER) behavior of the particle suspensions in silicone oil was investigated. The polarization ability of particles represented by the particle dipole coefficient increased greatly with the degree of hydrolysis of the nitrile component of SAN particles. As the acrylonitrile content of the copolymer particles was increased, the hydrolyzed particles exhibited higher dipole coefficients and, consequently, increased ER properties. Also, the effect of particle size on ER properties was studied by varying the size of these monodisperse copolymer particles.SEM photographs of nonhydrolyzed SAN50 microspheres (a) and the corresponding hydrolyzed SAN50 microspheres (b).water. For the recent decade, water-free ER fluids have been widely developed in order to overcome the disadvantages of aqueous systems. Anhydrous ER materials have some advantages such as system simplicity, reduced device corrosion, a relatively low current density, and a lower thermal coefficient of conductance, which may facilitate expanding the operating temperature range of ER activity. [7] Anhydrous ER fluids which...

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“…b Å (e d 0 e c ) (e d / 2e c ) , [1] Conventional electrorheological (ER) fluids are concentrated suspensions of micrometer-sized solid particles in in-in which e d is the dielectric constant of the particulate or sulating liquids (1)(2)(3)(4). As first reported by W. M. Winslow dispersed phase.…”

Section: Introductionmentioning

confidence: 98%