Using forced Rayleigh scattering, the tracer diffusion of methyl red through water and eight other solvents at different temperatures is investigated and the results are compared to the Cohen-Turnbull theory of free-volume diffusion. In seven solvents the effective non-Arrhenius activation energy measured experimentally agrees with the Cohen-Turnbull energy. In water, however, the diffusion can be described mathematically by the free volume model but there is a disagreement of more than an order of magnitude between these energies. We propose that the unique "zero point" free volume forced onto water by the strong hydrogen bonding requires a different mechanism for tracer motion.
Document Object Identifier (DOI)
Spiegel, D. R., Kollie, P. C., & Van Tilburg, S. J. (2014). Experimental tests of free-volume tracer diffusion in water and other solvents. Journal of Chemical Physics, 140(10).
Journal of Chemical Physics