Reverse Micelles Enable Strong Electrostatic Interactions Between Colloidal Particles in Nonpolar Solvents
Charge Stabilization in Nonpolar Solvents
M.F. Hsu, E. R. Dufresne, and D. A. Weitz
Langmuir 21 (2005) 4881-4887
wiki entry by Emily Russell, Fall 2010
The article can be found here.
Note: the citation on Eric Dufresne's page on the wiki is for the earlier arXiv version of this paper; this wiki entry is on the final version published in Langmuir. A brief glance shows the version to be similar, although the Langmuir paper has more content.
Overview and Comments
This paper discusses the crucial role of surfactants in allowing charge effects to be introduced into nonpolar solvents. The small dielectric constant of a nonpolar solvent means that it takes a good deal of energy to separate ions, so that salts would not be expected to dissociate and charge effects would be predicted to be negligible. Added surfactants, however, form reverse micelles, the cores of which can become charged; this allows colloidal particles to also obtain a charge. Because screening lengths in the low-dielectric solvents can be quite long compared to those in water, once a charge is stabilized, the effects can be significant. The authors point out that these charge interactions in nonpolar solvents have wide applications in electrophoretic inks (such as the Amazon Kindle uses).