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When Like Charges Attract

The above title implies that a basic law of physics has been overturned. Indeed, a commentary in Nature by C.A. Murray begins as follows:

"Larsen and Grier, on page 230 of this issue [Ref. 2], show that two similarly charged polymer spheres suspended in water can attract each other when they are several diameters apart. This surprising result casts some light on a tricky theoretical many-body problem that has been swept under the rug for a century, and it has implications for colloids in nature and in industrial processes." (Ref. 1)

Exactly what happens is not yet clear. This counter-intuitive phenomenon occurs in a many-body situation, where screening charges are established between the like-charged spheres. Although Coulomb's Law states that like charges repel one another, the presence of screening particles complicates the picture, as do the van der Waals dipole interactions.

The microscopic situation may be murky, but there is no doubt on the macroscopic level that unexpected attractive forces are operating. For example, when sub-microscopic, electrically charged latex spheres are suspended in water, one would expect a homogeneous colloidal soup. Instead, the tiny, charged spheres pull themselves together in patchy, but ordered arrays. These metastable groupings of spheres are called "crystallites." Theorists are not certain what is going on.

References

Ref. 1. Murray, Cherry A.; "When Like Charges Attract," Nature, 385:203, 1997.

Ref. 2. Larsen, Amy E., and Grier, David G.; "Like-Charge Attractions in Metastable Colloidal Crystallites," Nature, 385:230. 1997.

From Science Frontiers #112, JUL-AUG 1997. 1997-2000 William R. Corliss

Science Frontiers Sourcebook Project Reviewed in:

Quotes

  • "A sourcebook of unexplained phenomena is therefore a valuable addition to a collection of scientific literature. William R. Corliss has provided this in the past with his source books of scientific anomalies in several subjects, and now he has provided it for astronomy. He has done an excellent job of collecting and editing a large amount of material, taken in part from scientific journals and in part from scientific reporting in the popular or semi-scientific press." -- "The Mysterious Universe: A Handbook of Astronomical Anomalies", reviwed by Thomas Gold, Cornell University, in Icarus, vol.41, 1980

  • "An interesting, systematic presentation of unusual weather [..] This book is recommended for a general audience" --"Corliss, William R., Tornados, Dark Days, Anomalous Precipitation, and Related Weather Phenomena, Sourcebook Project, 1983.", revieweed in Choice, September 1983
  • "..the science is necessarily somewhat speculative, but Corliss's symthesis is based on reputable sources." -- "Corliss, William R. (Compiler). Lightning, Auroras, Nocturnal Lights, and Related Luminous Phenomena" reviwed by Joseph M. Moran, Univ. of Wisconsin in Science Books and Films, Sep/Oct 1983

  • "Before opening the book, I set certain standards that a volume which treads into dangerous grounds grounds like this must meet. The author scrupulously met, or even exceeded those standards. Each phenomenon is exhaustively documented, with references to scientific journals [..] and extensive quotations" -- "Book Review: The moon and planets: a catalog of astronomical anomalies", The Sourcebook Project, 1985., Corliss, W. R., Journal of the Royal Astronomical Society of Canada, Vol. 81, no. 1 (1987), p. 24., 02/1987