Cloud point transition in nonionic micellar solutions

Aqueous micellar solutions of the polyoxyethylene nonionic amphiphiles C6E3, C8E4, C12E8, and C14E7 have been investigated as a function of temperature and concentration by static and dynamic light scattering, turbidimetry, and viscosimetry. Light-scattering measurements at the critical concentration for phase separation show that the osmotic compressibility and the correlation range of concentration fluctuations diverge as the critical point is approached in all the investigated systems. The results concerning short-chain amphiphiles (C6E3, C8E4) strongly suggest that the observed behavior is due to critical concentration fluctuations and that the phase transition is due to interactions among small globular micelles. The results concerning long-chain amphiphiles (C12E8, C14E7) indicate that, besides critical effects, there may be some micellar growth with temperature. It is suggested that this second effect, if existing, is connected to the presence of anisotropic-phase boundaries not too far from the critical concentration line. © 1984 American Chemical Society