It is well-known that self-assembly of lipids and surfactants in water leads to structures such as micelles and vesiclesin dilute solution. In contrast, however, self-assembly in nonpolar organic solvents (oils) is much less studied. Standard textbooks in colloid science make only a brief mention of reverse micelles, which are typically assumed to be spherical. In the specialized literature, a few systems have been reported in which reverse spherical micelles can be transformed into reverse cylindrical micelles, typically upon addition of a polar substance like water. There is scant discussion of other non-micellar reverse phases such as reverse vesicles.In our laboratory, we have found that reverse self-assembly is a much richer subject than is known, and it is full of interesting and surprising findings. For example, we have found that simple salts can influence the reverse self-assembly of lipids in oil (salts can be dissolved in oil only in the presence of lipid). Moreover, the nature of the salt cation is found to critically influence reverse self-assembly. For example, in mixtures with the unsaturated phospholipid, soybean lecithin we have found that salts of multivalent cations such as Ca2+, Mg 2+, La3+ and Gd 3+induce the formation of reverse cylindrical filaments and in turn their organogels. This behavior is not seen with univalent cations like Na+ or K+ . Additionally, when combined with a saturated phospholipid, we have found that the same multivalent cations induce the formation of reverse multilamellar vesicles (reverse �onions�). Many of these results on reverse self-assembly can be rationalized based on molecular-geometry (packing parameter) principles, much like in the case of aqueous self-assembly.

From reverse micelles to reverse vesicles: Principles for modulating self-assembly in nonpolar organic solvents

245th National Meeting (2013)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.