Detection of critical micelle concentration (CMC) using uniform and U-shaped optical fiber in sensing region

Abstract

In this paper the critical micelle concentration (CMC) in surfactant solutions was detected by using an optical fiber. CMC detection is based on an adsorption effect in sample solution. The incident beam passing through the sensing region of the fiber reflected at the interface between the fiber core and the solution with repeating reflections. The change in adsorption condition leads to an effective change in the refractive index at the surrounding surface of the core. The output signal suddenly increases at the CMC due to the reflectivity change caused by adsorption of surfactant molecules onto the surface of the fiber. Plastic clad silica (PCS) fiber with a uniform sensing region was used to measure the CMC point in surfactant solution. It has been found that sensitivity of the sensor depends on the length of the sensing region, the launching condition of the light source and the optical fiber material. The higher the sensing length, the higher the sensitivity of the sensor. The U-shaped sensing region also tried to find the CMC point, and the experimental results indicate that the U-shaped sensing region is more sensitive than the uniform sensing region. Using this method we are able to detect the CMC of the surfactant solution very accurately and in real time.