The electrodipping force is a

force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can also be described intuitively as a p ...

proposed to explain the observed attraction that arises among small

colloidal A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend ...

particles attached to an interface between immiscible liquids. The particles are held there by

surface tension Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension is what allows objects with a higher density than water such as razor blades and insects (e.g. water striders) to f ...

. Normally the surface tension does not in itself give rise to an attraction or repulsion among particles on a

meniscus Meniscus may refer to: *Meniscus (anatomy), crescent-shaped fibrocartilaginous structure that partly divides a joint cavity *Meniscus (liquid) The meniscus (plural: ''menisci'', from the Greek for "crescent") is the curve in the upper surface ...

. A

capillary A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

interaction requires that the particles are pushed or pulled away from the meniscus, for instance because of their weight, if the particles are large and heavy enough. It has been proposed by Nikolaides et al. that the observed attractions are the result of an electrostatic pressure on the liquid interface, due to electric charges on the particles. The

electrostatic Electrostatics is a branch of physics that studies electric charges at rest (static electricity). Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber ...

pressure arises because the

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insulat ...

s of the liquids differ. Due to the pressure, the liquid interface deforms. This pressure is balanced by a simultaneous

electrostatic force Coulomb's inverse-square law, or simply Coulomb's law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is convention ...

acting on the charges, and hence on the particle itself. The force has been coined the ''electrodipping force'' by Kralchevsky et al. - it dips the particle in one of the liquids. According to Nikolaides, the electrostatic force engenders a long range capillary attraction. However, this explanation is controversial; other authors have argued that the capillary effect of the electrodipping force is in fact cancelled by the electrostatic pressure on the interface, so the resulting capillary effect would be insignificant.

References

# M. G. Nikolaides, A. R. Bausch, M. F. Hsu, A. D. Dinsmore, M. P. Brenner, C. Gay, D. A. Weitz, Electric-field-induced capillary attraction between like-charged particles at liquid interfaces, Nature 420, 299 (2002)
Physik
# K. D. Danov, P. A. Kralchevsky, M. P. Boneva, Langmuir 20, 6139 (2004) # M. Megens, J. Aizenberg, Nature 242, 1014 (2003), see # L. Foret, A. Wuerger, Physical Review Letters 92 58302 (2004), {{DEFAULTSORT:Electrodipping Force Fluid mechanics