Effect of flow reversal on the shear induced formation of multilamellar vesicles

The influence of rate controlled flow reversal on the transition from planar lamellae to multilamellar vesicles (MLV) using a nonionic lamellar phase consisting of 40 wt % triethylene glycol monodecyl ether (C10E3 in D2O) is investigated by means of time-resolved rheo-small-angle light and neutron scattering (SALS, SANS). Flow reversal provides the possibility to control the kinetics of the transition substantially, and states occurring very early during the transition can be studied. A slowing down of the transition on an absolute strain axis is observed as the strain amplitude of the flow reversal is decreased. This retardation is attributed to the partial recovery of an earlier state as shear is inverted. This can nicely be demonstrated by the width of the azimuthal intensity distribution, which shows oscillations upon flow reversal. From the slowing down of the process a loss term is defined, which provides insight in the very early stages of the experiment, namely the minimum strain that is needed to induce irreversible structural changes in the sample. This quantity is for the present sample found to be 6.5 strain units. Furthermore, the exponential scaling of the strain needed to reach characteristic states of the transition with strain amplitude seems to hold for all length scales involved in the process.