Mechanisms of the giant electrorheological effect

Huang, Xianxiang; Wen, Weijia; Yang, Shihe; Sheng, Ping

doi:10.1016/j.ssc.2006.04.042

Cited by 70 publications

(57 citation statements)

References 19 publications

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“…The resulting electrical energy density yields an excellent account of the observed GER yield stress variation as a function of the electric field. Electrorheological (ER) fluids [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] are a type of colloidal dispersions which can vary their rheological characteristics through the application of an external electric field. The traditional ER mechanism is based on induced polarizations arising from the dielectric constant contrast between the solid particles and the fluid [6,12].…”

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confidence: 99%

“…The recent discovery of the giant electrorheological (GER) effect [7][8][9][10][11][12], in urea-coated barium titanyl-oxalate nanoparticles ½NH 2 CONH 2 @BaTiOðC 2 O 4 Þ 2 , or BTRU for short, dispersed in silicone oil, has shown that the theoretical upper bound of the ER effect is no longer applicable to this new type of materials. Instead, a phenomenological model of the GER mechanism, based on aligned urea molecular dipoles in the small contact regions of the nanoparticles, yielded an adequate account of the observed effect [7,9,12]. However, a microscopic picture of how this can occur has so far eluded persistent efforts.…”

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“…Formation of water filaments under constrained conditions may give rise to forces far stronger and longer in range than the van der Waals interaction. We give a plausible speculation on the fluctuation-induced molecular dipole alignment at the end of this Letter.Owing to the nonideal thermodynamic nature of the urea-water solution, it is known that urea molecules tend to predominantly aggregate at the surface of hydrophilic solid particles [16,17], forming a (nonuniform) liquidlike coating [9]. Accordingly, we simulate our system of nanoparticles' contacts by two parallel bounding substrates, separated by a 2.9 nm gap.…”

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Giant Electrorheological Effect: A Microscopic Mechanism

et al. 2010

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Electrorheological fluids constitute a type of colloids that can vary their rheological characteristics upon the application of an electric field. The recently discovered giant electrorheological (GER) effect breaks the upper bound of the traditional ER effect, but a microscopic explanation is still lacking. By using molecular dynamics to simulate the urea-silicone oil mixture trapped in a nanocontact between two polarizable particles, we demonstrate that the electric field can induce the formation of aligned (urea) dipolar filaments that bridge the two boundaries of the nanoscale confinement. This phenomenon is explainable on the basis of a 3D to 1D crossover in urea molecules' microgeometry, realized through the confinement effect provided by the oil chains. The resulting electrical energy density yields an excellent account of the observed GER yield stress variation as a function of the electric field. Electrorheological (ER) fluids [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] are a type of colloidal dispersions which can vary their rheological characteristics through the application of an external electric field. The traditional ER mechanism is based on induced polarizations arising from the dielectric constant contrast between the solid particles and the fluid [6,12]. The recent discovery of the giant electrorheological (GER) effect [7][8][9][10][11][12], in urea-coated barium titanyl-oxalate nanoparticles ½NH 2 CONH 2 @BaTiOðC 2 O 4 Þ 2 , or BTRU for short, dispersed in silicone oil, has shown that the theoretical upper bound of the ER effect is no longer applicable to this new type of materials. Instead, a phenomenological model of the GER mechanism, based on aligned urea molecular dipoles in the small contact regions of the nanoparticles, yielded an adequate account of the observed effect [7,9,12]. However, a microscopic picture of how this can occur has so far eluded persistent efforts. Moreover, as the GER effect is highly sensitive to whether the dispersing oil can wet the solid particles [10,11], in contrast to the traditional ER fluids, a natural question is how this observation can be integrated into a coherent GER mechanism. In view of the fact that the GER effect has now been reproduced in many different material systems and therefore is becoming a much more general effect [14,15], answers to the above questions would not only be timely, but may also shed light on how to devise general strategies for harnessing and controlling the large electric energy stored in molecular dipoles.In this work we use molecular dynamics (MD) simulations to show that in a mixture of urea molecules with silicone oil chains confined between two bounding surfaces (denoted as substrates below) of a nanoscale contact, aligned urea molecular dipoles can form filaments snaking through the pores of the oil film to bridge the substrates. The required electric field for aligning the urea dipoles is found to be lowered by a factor of 2 to 3 in the presence of the oil chains, compared to that without the oil chains. More...

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Giant Electrorheological Effect: A Microscopic Mechanism

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“…These findings revealed that the primary structure of particle chains in the suspension controlled by compatibility of components may considerably influence the ER performance [11]. It is clear that a very high rjE [12] need not a priori mean a great relative increase in ER viscosity.…”

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confidence: 87%

Effect of hydrophilicity of polyaniline particles on their electrorheology: Steady flow and dynamic behaviour

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et al. 2010

Journal of Colloid and Interface Science

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A B S T R A C TElectrorheological properties of suspensions are considerably affected by hydrophilicity of suspension particles. As a model material, polyaniline base powder protonated with sulfamic, tartaric, or perfluo-rooctanesulfonic acids provided particles of various hydrophilicity. The experiments revealed that, in the absence of electric field, due to a good compatibility of hydrophobic polyaniline particles with sili-cone-oil medium, their interactions were limited and the viscosity of suspension was low. When the electric field was applied, the rigidity of the polarized chain structure of the particles increased and, consequently, viscosity increased as well. In the contrast, the field-off suspension viscosity of highly interacting hydrophilic particles, which are incompatible with the oil, and where particle aggregation may set in, was high especially at low shear rates, and the material had a pseudoplastic character. Then, a relative increase in viscosity due to the polarization of the particles or their clusters in the electric field was much lower than in the former case. Due to a different primary structure of suspension, depending on the particle compatibility with the oil the field-off storage modulus of suspensions of hydrophobic particles was lower than the loss modulus, while in suspensions of hydrophilic particles the former modulus dominated. In both cases, an increase in elasticity with increasing electric field strength was higher than that in viscosity.

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“…This fast, strong and reversible response allows the development of simple and efficient electromechanical systems able to control vibrations and dissipate energy in shocks [26,27]. However, the development of applications has been hindered due to the weakness of the Electrorheological effect (<10 kPa, much below 30 kPa required by many mechanical devices [28]) until the discovery of the giant electrorheological (GER) effect [29], which can reach a yield strength (>10 kPa [28]) above the theoretical upper bound on conventional ERFs. Additionally, while the static yield stress of ERFs shows a quadratic dependence on the electric field, GER effect exhibits a quasi-linear dependence [30].…”

Section: Electrorheological Fluidsmentioning

confidence: 99%

Complex Fluids in Energy Dissipating Systems

Galindo-Rosales

2016

Applied Sciences

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Abstract:The development of engineered systems for energy dissipation (or absorption) during impacts or vibrations is an increasing need in our society, mainly for human protection applications, but also for ensuring the right performance of different sort of devices, facilities or installations. In the last decade, new energy dissipating composites based on the use of certain complex fluids have flourished, due to their non-linear relationship between stress and strain rate depending on the flow/field configuration. This manuscript intends to review the different approaches reported in the literature, analyses the fundamental physics behind them and assess their pros and cons from the perspective of their practical applications.

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Mechanisms of the giant electrorheological effect

Cited by 70 publications

References 19 publications

Giant Electrorheological Effect: A Microscopic Mechanism

Giant Electrorheological Effect: A Microscopic Mechanism

Effect of hydrophilicity of polyaniline particles on their electrorheology: Steady flow and dynamic behaviour

Complex Fluids in Energy Dissipating Systems

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