THERMODYNAMICS OF MICELLIZATION OF A NONIONIC SURFACTANT MYRJ-45 - EFFECT OF ADDITIVES

Critical micelle concentrations of the non-ionic surfactant Myrj 45 in aqueous solution at various temperatures (35, 40, 45 and 50 degrees C ) were determined by the iodine solubilization method. A few systems w ere also studied by direct surface tension measurement. The effect of additives, e.g. PEG 400, sucrose, acetamide and urea, on the CMC was s tudied. The free energy, enthalpy and entropy of micellization were de termined. A negative free energy and a positive entropy of micellizati on were observed for all the systems. The micellization process was ex othermic in all cases except in aqueous solution without additives, wh ere the process was endothermic. An enthalpy-entropy compensation effe ct was observed for all the systems. Transfer enthalpies and heat capa cities were evaluated from enthalpy of micellization data. The transfe r enthalpy Delta H-m,H-tr was negative throughout, indicating the tran sfer of hydrophilic groups from water to the aqueous additive solution s. A maximum observed in the plot of Delta C-p,C-m,C-tr-concentration of additives was ascribed to a micellar structural transition.