Spherical Micelles of the surfactant DTAB, which has a cationic head, will turn into cylindrical micelles if the repulsion between the cationic heads can be reduced. I have read that adding salt (perhaps NaCl or NaBr) to this water/surfactant solution will reduce repulsion between the cations, thus triggering the change in shape. Can someone explain how adding salt would reduce coulombic forces between molecules? Salt is supposed to reduce the dielectric constant of water. Coulombic forces are inversely proportional to the dielectric constant, meaning adding salt should INCREASE repulsion. Or is the more relevant mechanism here simply that salt anions are attracted to the positive micelle surface, reducing net positive charge? Thanks!