Some context: A difunctional isocyanate diffuses into a solid surface of silicone rubber. Inside the silicone rubber, the isocyanate polymerizes with moisture to polyurea and changes its molecular weight and thus its diffusivity in the medium. The decreasing time dependence of the diffusion coefficient due to the change of the molecular weight was measured, as well as the time- and distance-dependent concentration distribution.
Question: Is there a solution for the non-steady-state unidirectional diffusion equation for a time- and distance-dependent diffusion coefficient? I've been working with Crank's standard solution for a constant diffusion coefficient and am now looking for a more detailed description.
Thanks in advance for tips of all kinds!!