title: Re-entrant lamellar/onion transition with varying temperature under shear flow.
abstract: We have found for the first time the reentrant lamellar/onion (lamellar-onion-lamellar) transition with varying temperature under constant shear rate by using simultaneous measurements of shear stress and small-angle X-ray scattering (Rheo-SAXS) for a nonionic surfactant (C(14)E(5))/water system, which exhibits the lamellar phase in a wide temperature range from 15-75 °C. The onion state exists in a closed region in the temperature-concentration diagram at a constant shear rate. Temperature dependence of the lamellar repeat distance (d) at rest has also been measured at several concentrations. It is shown that the increase of d with increasing temperature is necessary for the existence of the lower transition. We have investigated the change in the lamellar orientation in the lamellar-to-onion and onion-to-lamellar transition processes near the upper and lower transition temperatures. For all four kinds of transition processes, the following change in the lamellar orientation is observed; lamellar state (oriented to the velocity gradient direction) ↔ further enhancement of the orientation to the velocity gradient direction ↔ enhancement of the orientation to the neutral direction ↔ onion state.
authors.affiliation: Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo 192-0397, Japan.
authors.forename: Daijiro
authors.initials: D
authors.lastname: Sato
authors.forename: Kahoru
authors.initials: K
authors.lastname: Obara
authors.forename: Youhei
authors.initials: Y
authors.lastname: Kawabata
authors.forename: Makio
authors.initials: M
authors.lastname: Iwahashi
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kato