Direct Evidence for the Energy of Weak Interactions between Surfactant Molecules Using High Sensitivity Isothermal Titration Calorimetry

Calorimetry is a direct experimental method that can be used to study the thermodynamics of weak interactions between surfactant molecules, allowing the energetic parameters of such interactions to be obtained. In this work, a nano-isothermal titration calorimeter with a thermostat (TAM III) was used to evaluate the thermodynamic behavior of molecular self-assemblies of single and mixed surfactants in aqueous solution. Electrical calibration of this instrument showed that its precision is better than ±0.09%. The accuracy of the system was tested by measuring the reaction heat of tris-hydroxymethyl- aminomethane (Tris), employed often as a calorimetric standard substance, with hydrochloric acid. The resulting value ((-47.48±0.12) kJ·mol - 1 ) agreed well with that in the literature. We then determined the critical micelle concentration (cmc) and enthalpy of micellization for dodecyltrimethylammonium bromide