Inverse toroidal vesicles: precursors of tubules in sorbitan monostearate organogels

Sorbitan monostearate organogels are opaque, thermoreversible semi-solids w hose microstructure consists of surfactant tubules dispersed in the organic continuous phase. Inverse toroidal vesicles are the precursors of the surf actant tubules. The gelation process was observed as an isotropic sol phase of sorbitan monostearate in isopropyl myristate was cooled using hot-stage light microscopy. At the gelation temperature, inverse toroidal vesicular structures were seen to grow in the organic phase. These toroids are though t to be analogous to other well-known vesicles, liposomes and niosomes, exc ept for their toroidal (rather than spherical) shape and their inverse natu re. They are rather short-lived structures: on further cooling of the sol p hase, tubules form in the organic medium: it is speculated that the toroids elongate into tubular shapes or split into rod-shaped segments. (C) 1999 E lsevier Science B.V. All rights reserved.