Hi, I am solving the diffusion equation using explicit finite difference to model the diffusion of an analyte through a membrane. I am interested in the concentration of the analyte on the other side vs time elapsed. On one side of the membrane is an initial concentration, which I am implementing as a Dirichlet boundary condition, and the other is zero concentration of the analyte, in a blank solution. The initial condition of this other side would be 0, however I am unsure what the boundary condition would be. My first assumption would be a Neumann zero-flux boundary condition, however I don't know if this is correct. Any help on this would be great, thanks.