Examination and Improvement of Undergraduate Laboratory Experiment: Thermodynamics of a Surfactant Micellization

Thermodynamic characterization of micelle formation from an ionic surfactant in aqueous solutions is a classic experiment in physical chemistry. The critical micelle concentration (CMC) and the degree of micelle ionization (alpha) can be directly obtained by conductimetry, then thermodynamic parameters (Delta G(m)(o), Delta H-m(o), Delta S-m(o)) are deduced from the CMC values at different temperatures. Herein, the CMC values at different temperatures were generated by multiple student groups, and the resulting errors were combined with the enthalpy calculation error for micelle formation (Delta H-m(o)). Under the presented model it was found that Delta H-m(o) data were very difficult to obtain using the conductivity method. The isothermal titration microcalorimetry (ITC) method gave a direct Delta H(m)(o )value, which was incorporated into the experiment to determine the accuracy of the surveyed data. The introduction, design, and improvement of a "thermodynamics of 1-tetradecyl-3-methylimidazolium bromide (C-14 mimBr) micellization" experiment using conductivity and ITC methods were proposed, which may also improve students' experimental ability, practical skills, and quality of research.