NEGATIVE MAXWELL-STEFAN DIFFUSION-COEFFICIENTS

The existence of negative Maxwell-Stefan diffusivities is investigated . For the case where the diffusion coefficients are taken to be compos ition dependent, it is found that the theory of irreversible thermodyn amics does not require all diffusivities to be positive definite. This theoretical result is supported by literature diffusion coefficients in electrolyte solutions, which are composition dependent, and by one mixed-salt system which exhibits negative like-like ion diffusion coef ficients. Further, an approximate method of obtaining like-like ion di ffusion coefficients from tracer diffusivities is used to investigate a further 35 salt systems. In most of these systems negative diffusion coefficients do occur. The only exceptions are systems containing Hions and systems containing like ions of different valency. Finally, d iffusion coefficients of a co-ion in an ion exchange membrane, which a lso shows negative diffusion coefficients, are provided.