Micelle and oligomer kinetics in aqueous solutions of n-octylammonium chloride: Monomer exchange, protrusion and chain isomerization

Based on measurements of ultrasonic spectra in the frequency range between 0.1 and 2000 MHz the ultrasonic relaxation properties of solutions of the short-chain cationic surfactant n-octylammonium chloride in water are reported at solute concentrations between 0.18∙10− 3 mol cm− 3 and 1.6∙10− 3 mol cm− 3. Two relaxation terms are evaluated in the light of the fast monomer exchange of the Aniansson-Wall-Teubner-Kahlweit model of micelle kinetics. Significant effects of the incomplete dissociation of counter ions as well as of the large oligomer content at surfactant concentrations near the critical micelle concentration are shown and effects from the formation of non-globular micelles at higher surfactant concentrations are discussed. Two high-frequency relaxation terms are briefly considered with respect to monomer exchange of oligomers, fluctuating protrusion, and structural isomerisation of surfactant alkyl chains.