Study of the micelle-to-vesicle transition and smallest possible vesicle size by temperature-jumps

We have investigated the temperature induced micelle-to-vesicle transition in a binary non-ionic surfactant/water system, for which the spontaneous curvature decreases with increasing temperature. Temperature jumps with variable rate were performed in a microwave oven, from a micellar phase at 5°C to a lamellar phase region at 35°C, passing a liquid-liquid two phase region where dilute and concentrated micellar solutions coexist. It is shown that the obtained vesicle size decreases with increasing heating rate through this two phase region. Moreover, we demonstrate that there exists a minimum vesicle radius, Rv(∗), as is also predicted by theory. In the present system we find Rv(∗)≈50nm, in reasonable agreement with a theoretical estimate.