Simple liquid-liquid diffusion coefficient measurement system based on refractive index gradients

Interdiffusion between two liquids with different refractive index measurement system has been carefully constructed by using laser beam deflection method. The deflection pattern comes from refraction of the beam when it enters the interface of two different refractive index liquids. The diffusion coefficient is determined by observing refractive index gradients of liquid-liquid on the interface. In this phenomenon, mass transfer from liquid to liquid plays an important role and described using the Fick's law. The diffusion experiments have been performed with NaCl-aqueous solution. Interestingly, we found the diffusion coefficient of NaCl in reasonably good agreement with coefficient values specified in the literature. With simple setup and data analysis, we believe that the measurement system can be used to observe mass transfer in liquid accurately.