ABSORPTION OF LIQUID BY A SPHERE WITH SUBSEQUENT CHANGE IN DIMENSION,WITH RADIAL DIFFUSION AND FINITE SURFACE COEFFICIENT OF MASS-TRANSFER

When a polymer is in contact with a fluid, the fluid may enter the pol ymer and diffuse through it with a subsequent change in dimensions. Fi ck's second equation resulting from the mathematical treatment of diff usion was established with constant dimensions, meaning that absorptio n or desorption of a substance is not associated with a change in volu me of the solid. A general theory of diffusion is established by consi dering the change in dimensions in the case of a spherical solid, with various values of the coefficient of mass transfer on the surface. Th us Fick's second equation becomes a particular simple case of this gen eral theory. The problem can be solved by using a numerically explicit method with finite differences. The effect of the amount of substance absorbed on the process is especially considered.