Tracer diffusion in rubber + benzene mixtures and its relation to mutual diffusion

The tracer diffusion coefficient of radioactive benzene in mixtures of benzene and rubber at 25°C has been measured over the whole range of composition. The variation of diffusion coefficient with composition can be described by a formula of the Fujita type. The results have been combined with published values of the mutual diffusion coefficient and the thermodynamic properties. They are interpreted in terms of a “one-process” theory and show that the mobility of benzene molecules in mutual diffusion at low concentrations of rubber is greater than that in tracer diffusion by a factor which rises to 4.2 when the concentration of rubber is 5 %. The results are incompatible with the “two-process” theory of diffusion, unless this theory is modified by inclusion of an adjustable parameter.