Influence of temperature and oil-to-surfactant ratio on micellar growth inaqueous solutions of C12E5 with decane

The influence of temperature and of added oil on the size and shape of mice lles in the isotropic L-1 phase of the system pentaethyleneglycol-monododec ylether (C12E5) + water + decane has been investigated by static and dynami c light scattering. The micellar growth as a function of the solute concent ration was studied for oil-free aqueous solutions of C12E5 and for oil-cont aining micellar solutions at fixed mass fraction (alpha = 0.10) of the oil in the oil + surfactant mixture at three temperatures (13, 19 and 22 degree s C). In the oil-free system, the mean molar mass of the wormlike micelles, M-W, decreases as temperature is lowered at fixed concentration. This tren d is enhanced in the oil-containing system (alpha = 0.10), and a transition from oil-swollen wormlike micelles to microemulsion droplets is observed w hen the temperature is lowered from 19 to 13 degrees C. However, at 13 degr ees C the oil-swollen micelles are apparently not spherical, and droplet mi croemulsions that behave like a hard-sphere system are observed only when t he oil-to-surfactant ratio is increased beyond alpha = 0.10. (C) 2000 Elsev ier Science B.V. All rights reserved.