Dynamic light scattering for the determination of linoleic acid critical micelle concentration. Effect of pH, ionic strength, and ethanol

The present work proposes the use of Dynamic Light Scattering (DLS) to characterize aqueous solutions containing linoleic acid (LA). The parameters affecting CMC, particle size and distribution are studied. In a 0.2 M borate buffer, a CMC value of 0.13 ± 0.01 mM was found, with particle size increasing from 200 to 800 nm with LA concentration. It appears that increasing the pH does not simply affect the CMC value but also modifies the stabilization of the particles. At pH 9, the medium is monodisperse and, at the highest LA concentrations studied, vesicle formation is suspected. At pH values around 10-11, the medium is polydisperse due to the dynamic equilibrium of micelle formation/disintegration. The counter ion concentration (Na+) has a significant effect on the particles size and number. The addition of ethanol also has an effect on the stability of the particles and leads to a decrease of the particle size without significantly affecting the CMC value.