Permeation and self-diffusion in smectics A

2014 Recent R.M.N. and quasi-elastic neutron scattering experiments on smectics A have given comparable values for the self-diffusion coefficients D~ (diffusion normal to the layers) and D~, in spite of the possible occurence of a permeation process which would lead to much lower values for D ~. It is shown that there is no permeation in a self-diffusion experiment, and therefore that the Einstein relation connects D~ to an effective viscosity ~~ but not to the permeation coefficient 03BBp, which explains the experimental results. LE JOURNAL DE PHYSIQUE LETTRES TOME 37, JUIN 1976, Classification Physics Abstracts 7.130