Temperature dependence of critical micelle concentration of polyoxyethylenated non-ionic surfactants

The critical micelle concentrations (CMCs) of an n-dodecyl polyoxyethylene glycol monoether (C12H25O(C2H4O)(j)H) with three different oxyethlyene chain length ((j)= 4, 6 and 8) are experimentally determined over the temperature ranging from 10 degrees C to 80 degrees C using the Wihelmy plate technique. It is found that there exists a minimum CMC in the CMC-temperature curve. The temperature of the minimum CMC for three systems is around 50 degrees C. The enthalpy and entropy of micelle formation are evaluated. The correlation of enthalpy and entropy of micelle formation exhibits an excellent linearity, and the compensation temperature is 321 K, dramatically larger than previous findings for non-ionic surfactants in aqueous solutions. (C) 1998 Elsevier Science B.V.