  While the important role of electrostatic interactions in aqueous colloidal
suspensions is widely known and reasonably well-understood, the relevance of
charge in nonpolar suspensions remains mysterious. We demonstrate that
particles can have surprisingly strong electrostatic interactions in low
dielectric constant environments when ions are solubilized by reverse micelles.
A simple thermodynamic model, relating the structure of the micelles to the
equilibrium ionic strength, is in good agreement with both conductivity and
interaction measurements. Since dissociated ions are solubilized by reverse
micelles, the entropic incentive to charge a particle surface is qualitatively
changed, and surface entropy plays a important role.
