Electrorheological Fluids: Structure Formation, Relaxation, and Destruction

1991 ◽  
Vol 248 ◽  
Author(s):  
Thomas C. Halsey
Keyword(s):  
Electric Field ◽  
Structure Formation ◽  
Colloidal Particles ◽  
Strong Electric Field ◽  
Columnar Structure ◽  
Electrorheological Fluids ◽  
Qualitative Behavior ◽  
Ordered Structures ◽  
Dipolar Particles ◽  
Oriented Parallel

AbstractIn a strong electric field, the qualitative behavior of electrorheological fluids is dominated by the dipolar interactions between the colloidal particles. When thermal effects can be ignored, the ground state of a system of dipolar particles is an ordered solid. However, long-range ordered structures are rarely seen in experiment. When a high electric field is applied to a fluid, dielectric columns oriented parallel to the field rapidly form. The relaxation of these columns is a much slower process. I calculate the shape of the columns formed and the time scale for the relaxation of the columnar structure. I also discuss how this structure formation is altered in the presence of a shear flow.

MONODISPERSE COLLOIDAL SUSPENSIONS OF SILICA AND PMMA SPHERES AS MODEL ELECTRORHEOLOGICAL FLUIDS: A REAL-SPACE STUDY OF STRUCTURE FORMATION

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2328-2333 ◽  
Author(s):  
ANAND YETHIRAJ ◽  
ALFONS VAN BLAADEREN
Keyword(s):  
Electric Field ◽  
Structure Formation ◽  
Colloidal Particles ◽  
Intermediate Phase ◽  
Finite Size ◽  
Colloidal Suspensions ◽  
Real Space ◽  
Three Dimensions ◽  
Electrorheological Fluids ◽  
Crystal Formation

Colloidal particle coordinates in three dimensions can be obtained in 3D samples with a combination of the increased resolution and optical sectioning capabilities of confocal microscopy and fluorescently labeled model core-shell silica colloids. In this work we show how this capability can be used to analyze structure formation in electrorheological fluids on a quantitative basis. We find body-centered-tetragonal (BCT) crystals for colloidal particles in an electric field. Metastable sheet like structures were identified as an intermediate phase prior to BCT crystal formation. Due to finite-size effects induced by the electrode surface the sheets are not randomly oriented, but grow preferentially with a 60° tilt with respect to the electric field. Preliminary measurements indicate that flow-aligned sheets form under shear. Finally, we show that in the case that the ionic strength is very low, electric-field-induced dipolar interactions can be present in addition to long-range repulsions between the colloids leading to interesting metastable and equilibrium structures with possibilities for applications in photonic bandgap crystals as well as in model ER studies.

Characteristic Times of Microsturcture Formation in Electrorheological Fluids, Determined by Viscosity and Speckle Activity Measurements

2005 ◽  
Vol 15 (1) ◽  
pp. 38-45 ◽  
Author(s):  
Elvio Alanis ◽  
Graciela Romero ◽  
Carlos Martinez ◽  
Liliana Alvarez ◽  
Magdalena Mechetti
Keyword(s):  
Electric Field ◽  
Structure Formation ◽  
Apparent Viscosity ◽  
Light Transmission ◽  
Silicone Oil ◽  
Speckle Pattern ◽  
Electrorheological Fluids ◽  
Microstructure Formation ◽  
Electrical Field ◽  
Activity Measurements

AbstractViscosity measurements of a suspension of cornstarch in silicone oil, at several concentrations and subject to different electrical field strengths, were conducted. An increase in the apparent viscosity, in correlation with the field strength, which is characteristic of the so-called electrorheological fluids (ERF), was observed. For a given field intensity, the value of the viscosity increases rapidly in the first seconds after the application of the electric field, and then it increases slowly until it finally approaches a saturation value. This behaviour of the apparent viscosity has been related to the microstructure formation due to interactions between dipoles induced by the electric field. Characteristic times, related to structure formation after application of an electric field, are investigated by means of diffuse light transmission and speckle-pattern activity measurements. Two characteristic times were found that should be related to the state of aggregation of the suspended particles: orientation of the non-isotropic particles and later chain formation. These results agree reasonably with that obtained from electrorheological measurements. Microscopic observations of structure formation are also reported.

scholarly journals Axion assisted Schwinger effect

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Valerie Domcke ◽  
Yohei Ema ◽  
Kyohei Mukaida
Keyword(s):  
Electric Field ◽  
Production Rate ◽  
Strong Electric Field ◽  
Background Field ◽  
Chiral Anomaly ◽  
Fermion Mass ◽  
Anomaly Equation ◽  
Electric And Magnetic Fields ◽  
Schwinger Effect ◽  
Momentum Transverse

Abstract We point out an enhancement of the pair production rate of charged fermions in a strong electric field in the presence of time dependent classical axion-like background field, which we call axion assisted Schwinger effect. While the standard Schwinger production rate is proportional to $$ \exp \left(-\pi \left({m}^2+{p}_T^2\right)/E\right) $$ exp − π m 2 + p T 2 / E , with m and pT denoting the fermion mass and its momentum transverse to the electric field E, the axion assisted Schwinger effect can be enhanced at large momenta to exp(−πm2/E). The origin of this enhancement is a coupling between the fermion spin and its momentum, induced by the axion velocity. As a non-trivial validation of our result, we show its invariance under field redefinitions associated with a chiral rotation and successfully reproduce the chiral anomaly equation in the presence of helical electric and magnetic fields. We comment on implications of this result for axion cosmology, focussing on axion inflation and axion dark matter detection.

Observation of the Avalanche of Runaway Electrons in Air in a Strong Electric Field

2012 ◽  
Vol 109 (8) ◽  
Author(s):  
A. V. Gurevich ◽  
G. A. Mesyats ◽  
K. P. Zybin ◽  
M. I. Yalandin ◽  
A. G. Reutova ◽  
...  
Keyword(s):  
Electric Field ◽  
Strong Electric Field ◽  
Runaway Electrons

Electric-Field Induced Formation of Superconducting Granular Balls

2002 ◽  
Vol 16 (17n18) ◽  
pp. 2529-2535
Author(s):  
R. Tao ◽  
X. Xu ◽  
Y. C. Lan
Keyword(s):  
Surface Energy ◽  
Electric Field ◽  
Liquid Nitrogen ◽  
Applied Electric Field ◽  
Strong Electric Field ◽  
Particle Surface ◽  
Cooper Pairs ◽  
Surface Charges

When a strong electric field is applied to a suspension of micron-sized high T c superconducting particles in liquid nitrogen, the particles quickly aggregate together to form millimeter-size balls. The balls are sturdy, surviving constant heavy collisions with the electrodes, while they hold over 106 particles each. The phenomenon is a result of interaction between Cooper pairs and the strong electric field. The strong electric field induces surface charges on the particle surface. When the applied electric field is strong enough, Cooper pairs near the surface are depleted, leading to a positive surface energy. The minimization of this surface energy leads to the aggregation of particles to form balls.

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