Probing molecular cages in polymeric gels using paramagnetic ions: Internal motion of cupric ion in a cage

The effect of high‐energy irradiation on the aqueous solutions of certain water soluble polymers, namely, poly(vinyl alcohol) and poly(ethylene oxide), brings about physical and chemical changes. The cross links or networks formed in the polymer chains cause gel formation. These gels are considered to be made up of cubic cells or molecular cages with size varying between 0.6 and 1.5 nm. Such cages have been recently probed using the paramagnetic ions of hydrated cupric as well as vanadyl ions and were studied by electron paramagnetic resonance (EPR) and pulsed EPR techniques. The time‐dependent EPR spectra of Cu2+ ions in the cages are analyzed in this study using specific motional models, employing the modified Bloch equations. Computer simulations show that the spin probe’s motion is governed by the segmental motion of the polymer chains.