After !1684 is merged, we will have unified diffusion container storage which is communicated between the diffusion laws and the volume variables. However I believe that the memory requirements are significantly with !1684 increased because both binary and effective diffusion coefficients are stored. Evaluate if it's possible to get rid of the diffusion coefficient interface in the volume variables. They should be only called by the effective laws (but I might be wrong). If this is the case then passing the free diffusion coefficient to the effective laws would be a possible solution. Note: although !1684 is not merged yet at the writing of this issue I believe it will be simpler to not add additional feature request to this branch at the moment because it's already very difficult to review due to it's large number of changes.