236,828 research outputs found
Structure and thermodynamics of platelet dispersions
Various properties of fluids consisting of platelike particles differ from
the corresponding ones of fluids consisting of spherical particles because
interactions between platelets depend on their mutual orientations. One of the
main issues in this topic is to understand how structural properties of such
fluids depend on factors such as the shape of the platelets, the size
polydispersity, the orientational order, and the platelet number density. A
statistical mechanics approach to the problem is natural and in the last few
years there has been a lot of work on the study of properties of platelet
fluids. In this contribution some recent theoretical developments in the field
are discussed and experimental investigations are described.Comment: 23 pages, 18 figure
Electrical controlled rheology of a suspension of weakly conducting particles in dielectric liquid
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.Comment: Article pour la conf\'{e}rence sur les charges d'espaces (CSC
6\`{e}me \'{e}dition) qui s'est d\'{e}roul\'{e}e \`{a} Tours du 3 au 7
juillet 2006. 6page
Colloidal Jamming at Interfaces: a Route to Fluid-bicontinuous Gels
Colloidal particles or nanoparticles, with equal affinity for two fluids, are
known to adsorb irreversibly to the fluid-fluid interface. We present
large-scale computer simulations of the demixing of a binary solvent containing
such particles. The newly formed interface sequesters the colloidal particles;
as the interface coarsens, the particles are forced into close contact by
interfacial tension. Coarsening is dramatically curtailed, and the jammed
colloidal layer seemingly enters a glassy state, creating a multiply connected,
solid-like film in three dimensions. The resulting gel contains percolating
domains of both fluids, with possible uses as, for example, a microreaction
medium
Ferrolubricants
Ferrolubricants have magnetized angstrom-size iron particles which stick oil to moving surfaces at all times, significantly reducing frictional wear. Magnetic fluids can be produced in families of various fluids having widely-varying chemical and physical properties
Criticality in strongly correlated fluids
In this brief review I will discuss criticality in strongly correlated
fluids. Unlike simple fluids, molecules of which interact through short ranged
isotropic potential, particles of strongly correlated fluids usually interact
through long ranged forces of Coulomb or dipolar form. While for simple fluids
mechanism of phase separation into liquid and gas was elucidated by van der
Waals more than a century ago, the universality class of strongly correlated
fluids, or in some cases even existence of liquid-gas phase separation remains
uncertain.Comment: Proceedings of Scaling Concepts and Complex Systems, Merida, Mexic
Theory of Suspension Segregation in Partially Filled Horizontal Rotating Cylinders
It is shown that a suspension of particles in a partially-filled, horizontal,
rotating cylinder is linearly unstable towards axial segregation and an
undulation of the free surface at large enough particle concentrations. Relying
on the shear-induced diffusion of particles, concentration-dependent viscosity,
and the existence of a free surface, our theory provides an explanation of the
experiments of Tirumkudulu et al., Phys. Fluids 11, 507-509 (1999); ibid. 12,
1615 (2000).Comment: Accepted for publication in Phys Fluids (Lett) 10 pages, two eps
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