The inhomogeneous diffusion of chemically crosslinked Polyacrylamide hydrogel based on poroviscosity theory

The diffusion of hydrogels is a phenomenon not only profound in novel applications of mechanical engineering but also very common in nature. Comprehensive studies of the swelling properties under stable states have been carried out in the past several years; however, ambiguities in the understanding of the kinetic behaviour of the diffusion phenomenon of hydrogels still remain. The potential applications of hydrogels are confined due to the lack of perceptiveness of the kinetic behaviour of diffusion in hydrogels. Based on our previous work, in this study, we initiate the theoretical kinetic study of the inhomogeneous diffusion of hydrogels. With poroviscosity introduced, we develop a theory for the inhomogeneous diffusion of hydrogels. After implementing this theory into the finite element solution, we could predict the water content in the hydrogel as a function of time and location. The quantitative prediction of the inhomogeneous diffusion and the formulas are given in the numerical study. Furthermore, the corresponding experiments are carried out to substantiate this theory. It can be observed that the theoretical prediction meets fairly well with our experimental data. Finally, we carry out a systematic parameter study to discuss the effect of three important parameters on the diffusion property. The increase of the interaction parameter is seen to constrain the diffusion while increase of the chemical potential is seen to facilitate the process. The change of the diffusion coefficient D, on the other hand, does not affect the process much. By comparing the conclusions above with the experimental data, we can narrow down the range of the values of χ and D.