Dynamic phase diagram and onion formation in the system C10E3/D2O

The influence of the shear on the lamellar phase, L, of the system C10E3/D2O was studied along an isoplethal path (40 wt.% C10E3) in the temperature range 25-42degreesC. A dynamic phase diagram was determined by steady-state rheometry, where by shear action the lamellar phase was transformed into multilamellar vesicles (MLVs) ("onions"). The location of "onions" in the dynamic phase diagram, depends only on the temperature and the applied shear rate, and not on the shear history. The classical lamellar phase structure is stable at rest and at low shear rates. When exposed to higher shear rates, the lamellar structure is transformed into onions. The transition from lamellae to onions is shifted to higher shear rates with increasing temperature. In a range of shear rates in between the stable lamellae and stable onion structure, the transition is incomplete. The transformation of lamellae into onions appears to be governed by the imposed strain, in agreement with earlier studies. The effect of temperature can be understood from the general property of nonionic surfactants where the monolayer spontaneous curvature decreases with increasing temperature. (C) 2003 Published by Elsevier B.V.