COMPARISON OF DIFFERENT METHODS FOR DETERMINING THE CRITICAL MICELL CONCENTRATION

Introduction. A micellization process is particularly needed for drug technology to design dosage forms with desired properties. The study of micelles has contributed to the discovery of new pharmaceutical areas, such as targeted drug delivery. The boundary between surfactants and micelles is small and is represented by the critical micelle concentration (CMC). There is no clear definition of CMC in the literature; the authors confine themselves to the certain concentration at which a significant number of micelles are formed. Uncertainty in the definition of CMC actualizes a comparative study of methods for its determination. Material and methods. Sodium oleate as a white powder (manufactured by Sigma Life Science Co.) was used as a modelling sample. This sample contained 0.5% admixture of alkali in its pure form NaOH. Calculations were carried out at a temperature of 19±1°C. The study of CMC determined parameters, such as electrical conductivity, particle size, viscosity, and optical density. Results. An electrical conductivity-solution concentration diagram and a viscosity-solution concentration one clearly show a sharp inflection. At the inflection point there is a sharp change in the properties of the solution, which is due to micelle formation. The determination of CMC from the change in properties, such as the particle size obtained by dynamic light scattering, yields a less pronounced result. Conclusion. The CMCs viscosimetrically and conductometrically determined were found to coincide and are 1.9•10-2 mol/l. Dynamic light scattering gives a value of 2.0•10-2–2.1•10-2 mol/l, which agrees with the data available in the literature.