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The swelling kinetics of polyelectrolyte gels with fixed[1] and variable degrees of ionization in salt-free
solvent is studied by solving the constitutive equation of motion of the spatially and temporally varying displacement
variable. Two methods for the swelling kinetics- the Bulk Modulus Method (BMM), which uses a linear stress-strain
relationship (and, hence a bulk modulus), and the Stress Relaxation Method (SRM), which uses a phenomenological expression
of osmotic stress, are explored to provide the spatio-temporal profiles for polymer density, osmotic stress, and degree of
ionization, along with the time evolution of the gel size. Further, we obtain an analytical expression for the elastic
modulus for linearized stress in the limit of small deformations. We match our theoretical profiles with the experiments
of swelling of PNIPAM (uncharged) and Imidazolium-based (charged) minigels available in the literature. |