Rapid measurement of liquid diffusion coefficients for different concentrations based on compound liquid-core cylindrical lenses and the finite element method

Liquid diffusion coefficients are usually concentration-dependent (D(C)), and current methods for measuring the D(C) relationship suffer from long measurement times and large repetitive experimental workloads. This paper consequently proposes a new method for rapid measurement of D(C), which can eliminate the need to measure uncalibrated diffusion coefficients corresponding to concentration by comparing the theoretical concentration distribution of diffusion solution obtained by the finite element method and the experimental concentration distribution. The core diffusion and imaging setup is a compound liquid-core cylindrical lens, which can offer the advantages of high refractive index resolution and imaging quality, guaranteeing the accurate measurement concentration distribution. The D(C) relationship can be obtained by simply gathering an appropriate diffusion image in one experiment profiting from taking full use of the solution concentration spatiotemporal distribution information using the finite element molding fitting method, reducing the measurement time greatly from several days in traditional methods to within 2 hours, characterized by short measurement time, high measurement accuracy and small experimental workload. The D(C) relationship of NaCl solution at 25 °C was measured using this method, and the result was in accord with the instantaneous image method and the literature values.