Boltzmann Transformation of Taylor Dispersion Profiles to Determine Concentration‐Dependent Diffusion Coefficients. Aqueous Cetylpyridinium Chloride near the Critical Micelle Concentration

The Taylor dispersion technique is modified to measure the concentration‐dependent mutual diffusion coefficient D of cetylpyridinium chloride (CPC) + water at 25°C near the critical micelle concentration. The solution flowing into the dispersion tube is changed from a solution of CPC concentration C − to a solution of concentration C − + Δ C , forming an initially‐sharp moving boundary at the tube inlet. The broadened concentration profile across the eluted boundary is followed by using a flow‐through differential refractometer at the tube outlet. A numerical procedure similar to the Boltzmann‐Matano procedure for the analysis of free diffusion profiles yields the values of D at the concentrations between C − and C − + Δ C , from a single dispersion run. D for aqueous CPC is found to drop very sharply as the concentration is raised through the critical micelle concentration.