The penetration depth of the functional group and the intraparticle diffusivity of a transition metal cation (Cu2+) have been determined for sub-micron-sized electrospun alkali hydrolyzed poly(acrylonitrile) ion-exchange fibers. The ion-exchange fiber's shell thickness, determined using a TEM coupled with EDX spectrophotometer, was 8-14 nm and it averaged similar to 11 nm. The intraparticle diffusivity obtained through numerical simulation for the bidirectional transport of ions into and out of the fiber, i.e., for uptake as well as regeneration kinetics, is in the order of 10(-20) m(2)/s.