TEMPERATURE-DEPENDENCE OF CRITICAL MICELLE CONCENTRATION OF POLYOXYETHYLENATED NONIONIC SURFACTANTS

The critical micelle concentrations (CMCs) of an n-dodecyl polyoxyethy lene glycol monoether (C12H25O(C2H4O)(j)H) with three different oxyeth lyene chain length ((j)= 4, 6 and 8) are experimentally determined ove r 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 i n the CMC-temperature curve. The temperature of the minimum CMC for th ree systems is around 50 degrees C. The enthalpy and entropy of micell e formation are evaluated. The correlation of enthalpy and entropy of micelle formation exhibits an excellent linearity, and the compensatio n temperature is 321 K, dramatically larger than previous findings for non-ionic surfactants in aqueous solutions. (C) 1998 Elsevier Science B.V.