Dynamical modeling and experimental evidence on the swelling/deswelling behaviors of pH sensitive hydrogels

A chemo-electro-mechanical fields coupling model was developed based on the Nernst–Planck equation, Donnan theory and elastic mechanics to investigate the swelling/deswelling dynamics of pH sensitive hydrogels. To test the model, chitosan hydrogels with pH sensitivity have been successfully prepared through a radiation crosslinking approach induced by Co-60 gamma ray. The deformation ratio of the hydrogels at radial direction is more than 100% when pH changes from 7 to 9. A finite element simulation was carried out to investigate the stress formation and diffusion inside the hydrogel in its deswelling process. Results showed that the data of simulation fit the experimental results well. Moreover, a stress-diffusion mechanism was proposed to explain the deswelling process.