Electrorheology: Mechanisms and models

Parthasarathy, M.; Klingenberg, Daniel J.

doi:10.1016/0927-796x(96)00191-x

Cited by 615 publications

(518 citation statements)

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“…Real-space microscopy and light scattering experiments have been carried out on crystal nucleation dynamics [5,6] as well as structure and dynamics at the colloidal glass transition [7][8][9]. In the presence of an external electric field, Brownian colloidal spheres experience an anisotropic dipolar interaction and form chains (the ''string fluid'') and multichain aggregates [10,11], as well as body centered tetragonal (BCT) crystals [12][13][14]. Multiple competing interactions lead to richer phase behavior.…”

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confidence: 99%

Low-Density Ordered Phase in Brownian Dipolar Colloidal Suspensions

Agarwal

Yethiraj

2009

Phys. Rev. Lett.

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We study the low volume fraction and electric field phase behavior of a Brownian colloidal suspension. On the application of a uniform ac field, we find a novel phase where chains of particles aggregate to form a well defined cellular network, consisting of particle-free ''voids'' surrounded by a percolating network of particle-rich walls. This cellular structure is stable to very long times, indicative of an equilibrium thermodynamic phase. The cell-cell spacing is not sensitive to the concentration of the sample but scales with sample thickness. Any self-consistent mechanism for the existence of this void phase must consist of long-ranged repulsions and shorter-ranged attractions. DOI: 10.1103/PhysRevLett.102.198301 PACS numbers: 47.57.JÀ, 64.70.pv Brownian colloidal suspensions with tunable interactions are important model systems for understanding phase transitions in atomic systems [1][2][3][4]. Real-space microscopy and light scattering experiments have been carried out on crystal nucleation dynamics [5,6] as well as structure and dynamics at the colloidal glass transition [7][8][9]. In the presence of an external electric field, Brownian colloidal spheres experience an anisotropic dipolar interaction and form chains (the ''string fluid'') and multichain aggregates [10,11], as well as body centered tetragonal (BCT) crystals [12][13][14]. Multiple competing interactions lead to richer phase behavior. In colloid-polymer mixtures both network-forming gel phases and glassy behavior can be observed by control of competing attractive and repulsive interactions [15,16]. Anisotropic interactions between colloids [17] in a liquid crystal medium also lead to a network of particle aggregates [18]. In dipolar colloids with added electrostatic repulsions, numerous crystalline phases are observed [19,20]. The dipolar interaction is of great interest because it consists of both competing on-axis (along the electric field) attractions and in-plane repulsions, and because it is an important driving force for nanoparticle selforganization [21].Simulations of spheres with both dipolar and van der Waals interactions have shown many variants (linear aggregates, droplets, columns) of phase separation into regions of higher and lower densities [22,23]. However, structure formation in the low-density regime of Brownian colloidal suspensions in an electric field has not attracted much experimental attention. Recently, interesting field induced cellular structures were reported in a granular medium [24], but the mechanism (and whether they represented equilibrium structures) was not clear.In this Letter, we report real-space confocal microscopy studies of the effect of an ac external electric field on the low-density structure of Brownian colloidal suspensions. We report the existence of a novel ''gel-like'' phase at low volume fractions ( < 4:0%) where chains of particles aggregate in time to form a cellular structure composed of ''voids''-particle-free domains enclosed completely by particle-rich walls. We propose that the co...

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confidence: 99%

Low-Density Ordered Phase in Brownian Dipolar Colloidal Suspensions

Agarwal

Yethiraj

2009

Phys. Rev. Lett.

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“…Here, ϕ : R + × R + → R stands for a viscosity function depending on the second invariant of the rate of deformation tensor and the electric field strength. The most commonly used constitutive law for simple flow modes is that of a Bingham-type fluid ATKIN et al [1991], FILISKO [1995], PARTHASARATHY and KLINGENBERG [1996], RHEE et al [2003], STANWAY et al [1996], WHITTLE, ATKIN and BUL-LOUGH [1995]. For stresses above a field dependent yield stress σ Y (E) the viscosity function ϕ is given by…”

Section: Mathematical Models For Electrorheological Fluid Flowsmentioning

confidence: 99%

“…Idealized electrostatic polarization methods obtain the electrostatic potential via Laplace's equation and compute the motion of the particles by Newton's equation which requires the proper specification of the total force exerted on a particle by taking into account the interparticle forces. Since the exact solution is unavailable and the computation of all possible interparticle forces is cumbersome, the system is simplified by the point-dipole approximation (see JONES [1995], KIM and KLINGENBERG [1997], PARTHASARATHY and KLINGENBERG [1996], PFEIL and KLINGENBERG [2004]) assuming that two spheres of the same size do not change their charge distributions. The resulting force equation only depends on the distance of the particles, the angle between them, the particle size, and on the properties of the induced electric field.…”

Section: Introductionmentioning

confidence: 99%

“…The results of the model differ by an order of magnitude from experimentally available data, since the dipole moment of the particles enhances the polarization. This has been accounted for in PARTHASARATHY and KLINGENBERG [1996] by a modified point-dipole approximation and by providing multipole models (see , CLERCX and BOSSIS [1993]) which are based on several electric field equations (up to four), whereas the particle interaction is performed for an N particle cluster allowing the consideration of particles in lattice structures such as body-centered tetragonal crystal lattices. The dipole-induced dipole model in YU and WAN [2000] represents a further development of the multipole models in so far as it admits spheres of different sizes.…”

Section: Introductionmentioning

confidence: 99%

“…The dipole-induced dipole model in YU and WAN [2000] represents a further development of the multipole models in so far as it admits spheres of different sizes. Maxwell-Wagner polarization due to accumulated charges between the interface of the particles and the continuous phase has been incorporated in PARTHASARATHY and KLINGENBERG [1996] by assuming a point dipole model for this interfacial polarization. The Maxwell-Wagner model in KHUSID and ACRIVOS [1995] further acknowledges effects of the disturbance field between particles.…”

Section: Introductionmentioning

confidence: 99%

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