SPONTANEOUS FORMATION OF ONION PHASES IN A SINGLE SURFACTANT SYSTEM AND THEIR SALT-INDUCED TRANSFORMATION TOWARDS ORDINARY LAMELLAR PHASES

Onion phases are lyotropic lamellar phases which contain regions in wh ich the surfactant bilayers are concentrically stacked like the layers in an onion. We report the spontaneous formation of such phases conta ining the single surfactant AOT and water. Upon addition of salt, a sp ontaneous transition to an ordinary lamellar phase is observed and thi s is explained quantitatively in terms of electric contributions to th e splay and saddle splay moduli of the bilayer.