  The properties of suspensions of fine particles in dielectric liquid
(electrorheological fluids) subjected to an electric field lead to a drastic
change of the apparent viscosity of the fluid. For high applied fields (~ 3-5
kV/mm) the suspension congeals to a solid gel (particles fibrillate span the
electrode gap) having a finite yield stress. For moderate fields the viscosity
of the suspension is continuously controlled by the electric field strength. We
have roposed that in DC voltage the field distribution in the solid (particles)
and liquid phases of the suspension and so the attractive induced forces
between particles and the yield stress of the suspension are controlled by the
conductivities of the both materials. In this paper we report investigation and
results obtained with nanoelectrorheological suspensions: synthesis of coated
nanoparticles (size ~ 50 to 600 nm, materials Gd2O3:Tb, SiOx...), preparation
of ER fluids (nanoparticles mixed in silicone oil), electrical and rheological
characterization of the ER fluids. We also propose a possible explanation of
the enhanced ER effect (giant ER fluids) taking into account the combined
effects of the (nano)size of the particles, the Van der Waals forces between
particles in contact and the electrostatic pressure in a very thin layer of
insulating liquid.
