The electrodipping force is a

force In physics, a force is an influence that can cause an Physical object, object to change its velocity unless counterbalanced by other forces. In mechanics, force makes ideas like 'pushing' or 'pulling' mathematically precise. Because the Magnitu ...

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 exten ...

particles attached to an interface between

immiscible Miscibility () is the property of two chemical substance, substances to mix in all mixing ratio, proportions (that is, to fully dissolution (chemistry), dissolve in each other at any concentration), forming a homogeneity and heterogeneity, homoge ...

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 (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...

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

capillary A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the inn ...

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 slow-moving or stationary electric charges. Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word (), mean ...

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 insul ...

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