Neutron spin echo measurements of the diffusion of water in porous solids

The tracer diffusion of a liquid in a porous media was studied using the neutron spin echo technique. The samples used consisted of porous Vycor glass saturated with a mixture of D 2 O-H 2 O (64/36) water to match out the coherent small-angle scattering component due to the neutron scattering density contrast between water and the Vycor matrix, in order to reduce the small-angle neutron scattering and the chemical diffusion contribution to the quasi-elastic scattering. A series of measurements has been made in the Q range 0.07-0.14 AA -1 using the spin echo spectrometer IN11 at the ILL. This experiment in principle enables us to measure the tracer diffusion coefficient of the liquid within a pore and through the local pore network and hence to investigate the interconnectivity of these pores through a determination of <r 2 (t)< over length scales to about 100 AA.