Association of caffeine in aqueous solution. Effects on caffeine intradiffusion

Abstract

Tracer-(intra-) diffusion coefficients of ¹⁴C-labelled caffeine, D_T, have been measured by the diaphragm-cell technique over the temperature range 37–80 °C and as a function of concentration to a maximum of 0.29 mol kg^–1 at 50 °C, extending earlier measurements at 25 °C. Limiting mutual diffusion coefficients, D^∞, have also been determined with the Taylor dispersion technique between 20 and 65 °C. The concentration dependence of the relative intradiffusion coefficients changes little above 37 °C, but is stronger at lower temperatures. The results are analysed with the aid of association models.