| Abstract | Fourier transform infrared spectroscopy is presented as a technique with great potential for the study of aqueous surfactants, especially when investigating structural changes brought about by a change in temperature or concentration. Micelle formation in aqueous surfactants can be induced by either an increase in concentration through the critical micelle concentration range, or by an increase in temperature through the critical micellization temperature. Due to the concentration range involved, (i. e. 0.1 to 0.3 M surfactant), infrared spectroscopy is particularly suitable for the study of the temperature-induced micellization, and we discuss herein details of the structural changes observed at the critical micellization temperature of a number of anionic surfactants. The thermotropic phase behavior of these aqueous surfactants was monitored via structural changes specific to the hydrophobic acyl chains and those of the hydrophilic carboxylate and sulfate head group moieties. The temperature-induced changes in infrared spectral parameters such as frequency and bandwidth characterize the critical micellization temperature of these surfactants as a phase transition from a conformationally ordered, solid-like phase to an isotropic micellar phase. The concept of a critical micellization temperature is discussed in relation to that of the Krafft point and the critical micelle concentration. |
|---|
