Electrorheological Fluid Dynamics

Zhang, Jianwei; Gong, Xiuqing; Liu, Chun; Wen, Weijia; Sheng, Ping

doi:10.1103/physrevlett.101.194503

Cited by 36 publications

(35 citation statements)

References 26 publications

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“…The energy variational treatment of complex fluids [8][9][10] starts with the energy dissipation law,…”

Section: ͒mentioning

confidence: 99%

“…8,9 Variational methods describe solid balls in liquids, deformable electrolyte droplets that fission and fuse, 1,10 and suspensions of ellipsoids, including the interfacial properties of these complex mixtures, such as surface tension and the Marangoni effects of "oil on water" and "tears of wine." 1, 7,11 Solid charged spheres such as sodium and chloride ions in water seemed to be a simpler fluid than deformable fissioning droplets ͑in some respects͒ and so we wondered if a͒ Author to whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

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Energy variational analysis of ions in water and channels: Field theory for primitive models of complex ionic fluids

Eisenberg

Hyon

2010

The Journal of Chemical Physics

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Ionic solutions are mixtures of interacting anions and cations. They hardly resemble dilute gases of uncharged noninteracting point particles described in elementary textbooks. Biological and electrochemical solutions have many components that interact strongly as they flow in concentrated environments near electrodes, ion channels, or active sites of enzymes. Interactions in concentrated environments help determine the characteristic properties of electrodes, enzymes, and ion channels. Flows are driven by a combination of electrical and chemical potentials that depend on the charges, concentrations, and sizes of all ions, not just the same type of ion. We use a variational method EnVarA (energy variational analysis) that combines Hamilton's least action and Rayleigh's dissipation principles to create a variational field theory that includes flow, friction, and complex structure with physical boundary conditions. EnVarA optimizes both the action integral functional of classical mechanics and the dissipation functional. These functionals can include entropy and dissipation as well as potential energy. The stationary point of the action is determined with respect to the trajectory of particles. The stationary point of the dissipation is determined with respect to rate functions (such as velocity). Both variations are written in one Eulerian (laboratory) framework. In variational analysis, an "extra layer" of mathematics is used to derive partial differential equations. Energies and dissipations of different components are combined in EnVarA and Euler-Lagrange equations are then derived. These partial differential equations are the unique consequence of the contributions of individual components. The form and parameters of the partial differential equations are determined by algebra without additional physical content or assumptions. The partial differential equations of mixtures automatically combine physical properties of individual (unmixed) components. If a new component is added to the energy or dissipation, the Euler-Lagrange equations change form and interaction terms appear without additional adjustable parameters. EnVarA has previously been used to compute properties of liquid crystals, polymer fluids, and electrorheological fluids containing solid balls and charged oil droplets that fission and fuse. Here we apply EnVarA to the primitive model of electrolytes in which ions are spheres in a frictional dielectric. The resulting Euler-Lagrange equations include electrostatics and diffusion and friction. They are a time dependent generalization of the Poisson-Nernst-Planck equations of semiconductors, electrochemistry, and molecular biophysics. They include the finite diameter of ions. The EnVarA treatment is applied to ions next to a charged wall, where layering is observed. Applied to an ion channel, EnVarA calculates a quick transient pile-up of electric charge, transient and steady flow through the channel, stationary "binding" in the channel, and the eventual accumulation of salts in "unstirred layers" ne...

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“…The energy variational treatment of complex fluids [8][9][10] starts with the energy dissipation law,…”

Section: ͒mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Energy variational analysis of ions in water and channels: Field theory for primitive models of complex ionic fluids

Eisenberg

Hyon

2010

The Journal of Chemical Physics

Self Cite

229

242

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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%

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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“…This argument has the consequence that the low value of D can be explained such that, due to the strongly inhomogeneous electric field, the growing clusters become more and more anisotropic and the aspect ratio increases as a power law of R g , i.e., χ ∼ R δ g . The exponent δ is an important characteristic quantity of the ER system [20,21], it demonstrates that the clusters of the ER system have a self-affine character, i.e., the larger they get, the more anisotropic they are [36][37][38]. In our system δ = 2 − D gives rise to the value δ = 0.75 of the self-affinity exponent.…”

Section: Structural Transition Of the Particle Systemmentioning

confidence: 61%

Percolation-induced conductor-insulator transition in a system of metal spheres in a dielectric fluid

Sun

Kun

2011

Phys. Rev. E

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We develop a model to investigate the insulator-conductor transition observed in a system of spherical metal particles suspended in a quasi-two-dimensional viscous liquid between planar electrodes when the voltage of the electrodes is increased. Our model captures the main ingredients of the process in experimental system, and reveals the insulator-conductor transition at a well-defined critical voltage. Based on the simulation data we demonstrate that characteristic quantities of the system show power-law scaling in the vicinity of the critical point. These scaling analysis show clearly that the transition between the insulating and conducting phases is analogous to second-order phase transitions.

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Electrorheological Fluid Dynamics

Cited by 36 publications

References 26 publications

Energy variational analysis of ions in water and channels: Field theory for primitive models of complex ionic fluids

Energy variational analysis of ions in water and channels: Field theory for primitive models of complex ionic fluids

Giant Electrorheological Effect: A Microscopic Mechanism

Percolation-induced conductor-insulator transition in a system of metal spheres in a dielectric fluid

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