Determination of Surfactant cmc Based on the Fiber Refractive Index Sensor Principle

A novel method for the determination of surfactant critical micelle concentration (cmc), based on the fiber refractive index sensor principle was studied. The cmc of a representative anionic surfactant sodium dodecyl sulfate (SDS) and the cmc of a cationic surfactant cetyltrimethylammonium bromide (CTAB) were found to be 8.05x10(-3) and 9.11x10(-4) mol . L-1 respectively at 25 degrees C using this method, which are in good agreement with literature values. Further determinations of surfactant cmc under various conditions show that the influence of temperature and the inorganic salt NaCl on the accuracy of the method is slight. Therefore, the applicability of the method is proven. We also tested the repeatability and stability of this method. The relative standard deviation (RSD) for the measurement results was 0.17%, which is consistent with our expectation.