STRUCTURE OF ELECTRORHEOLOGICAL FLUIDS
Ujitha Dassanayake
Seth Fraden
Brandeis University
We study the structure of electrorheological (ER) fluids
(ER Bibliography).
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ER fluids are colloidal suspensions of particles of size
1-100 microns in non-conducting solvents
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The viscosity of ER suspensions can increase 2-3 orders
of magnitude when electric fields ~1kV/mm are applied across them. The
response takes ~ 1ms. This increase in viscosity is attributed to the energy
required to disassociate the electric field induced structures.
As shown in the diagram below, an external electric field induces a
dipole oriented parallel to the field in a dielectric particles (a sphere
here), and dipoles interact such that they align themselves along the field
direction.
(below)Schematic of a ER suspension forming chains across electrodes
and undergoing shear:The force required to break apart the electric-field
induced structures manifests itself in an increase in viscosity.
from Klingenberg and
Zukoski, Langmuir 1990, 6, 15-24
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Because of the large increase in viscosity, and the rapid,
reversible viscous response, technological applications have been proposed
for ER fluids, in devices such as shock absorbers, clutches and valves.
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