The mechanism and kinetics of a shear-induced formation of multi-lamellar vesicles in a lyotropic lamellar phase of C10E3 (Triethyleneglycol-decylether) was investigated by rheology and time-resolved small-angle neutron and light scattering (SANS, SALS). Starting from a well-defined, macroscopically oriented lamellar phase, the transition occurs in two steps. First, there is a formation of an intermediate structure oriented in the flow direction which scatters only perpendicular to the flow. This is compatible with long, multi-lamellar cylinders (tubuli). Comparing results from three different shear rates shows that the formation of this intermediate structure is strain controlled. As shear is continued, multilamellar vesicles are formed.Introduction. -The influence of shear on the structure and orientation of complex fluids has attracted much interest in recent years [1,2]. Following the pioneering work of Diat et al. [3], particular attention has been given to lyotropic lamellar phases which exhibit two special features under shear. One is the flipping of aligned planar lamellae [4-10] and the second concerns the formation of multi-lamellar vesicles (MLVs) [3,[11][12][13][14][15][16][17][18]. While the shearinduced formation of MLVs has been demonstrated in many different systems, both with surfactants and with block copolymers [19], it is neither yet fully understood why they are formed, nor what the mechanism of the formation is. In the present paper we focus on the latter problem and present data from the so-called start-up experiments, where a well-defined, oriented lamellar state, having the bilayers aligned with their normal in the gradient direction, is suddenly exposed to shear of a constant rate. The structural evolution from lamellae to MLVs is followed by time-resolved i) viscosity measurements, ii) small-angle light scattering (SALS) and iii) small-angle neutron scattering (SANS).The system contains the surfactant C 10 E 3 (Triethyleneglycol-decylether) dissolved in heavy water (D 2 O). In this system, a lamellar (L α ) phase is stable at room temperature over a wide range of concentration. Below about 50 wt.% the lamellar phase coexists with an L 3 (sponge) phase at higher temperatures. In this lamellar phase, MLVs can be formed upon shearing, however, the stability, under shear, of the MLV state relative to a planar bilayer state depends

The effect of shear on the lamellar phase of amphiphilic systems has been widely studied in a variety of amphiphilic systems as a function of shear rate. In this investigation, we fixed the shear rate and performed temperature scan experiments on a two-component (C10E3-water) system. We observed a sequence of phases, from the low to high temperature range: multilamellar vesicle to planar lamellar to sponge phase. The shear-induced multilamellar vesicle (MLV) phase exhibited the most interesting behavior and is the main focus of the present study. Small-angle neutron and light scattering techniques were used to elucidate the microstructure, to determine the bilayer orientation, and to characterize the size of these structures. The interlamellar spacing was observed to be the same in the lamellar as in the MLV phase, and the MLV phase exhibited symmetrical scattering in the neutral and flow directions, indicating that the layers in the vesicles are spherically shaped at the selected shear rate (γ ˘) 100 s -1 ). With all the information that we could gather for the planar lamellar and MLV phases, we used the framework of the elastic curvature energy model to describe qualitatively the stability of these bilayer structures formed at a given shear rate.

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Different suggestions for the mechanism governing the narrow stability of the L(3) (sponge) phase have led to a series of debates in recent years. There have been several models developed to describe such a mechanism via thermodynamics. To date, experimental data are insufficient to test present theories. In this study, we revisit the sponge phase with two series of thermodynamic data performed on the well-characterized C(12)E(5)-n-decane-H(2)O system. These thermodynamic data sets stem from phase equilibrium and static light scattering experiments designed to link system-specific parameters such as the temperature dependence of the spontaneous curvature H(o) and the two bending moduli kappa and (-)kappa, which have only been loosely connected in earlier experiments. The use of a well-characterized system is important in that it allows usage of molecular descriptors from earlier studies to reduce fit parameters. Another advantage for using this system is that its phase behavior is analogous to a two-component system which, from an experimental standpoint, is more practical to perform accurate measurements and, from a theoretical standpoint, more simple to model. In the present investigation, we use these tools to quantitatively test parameters obtained by different experimental techniques and assumptions inherited in theoretical models designed to interpret them.