The fast homogeneous diffusion of hydrogel under different stimuli

Hydrogels possess marvellous properties which may be harnessed for novel applications in mechanical engineering. In the deformation study of hydrogel, the diffusion of hydrogel is an extremely common phenomenon. The stable state study of the swelling property has been studied intensively during the past decade, yet the kinetic behaviour of the diffusion phenomenon of hydrogel remains evasive. The lack of understanding of the kinetic behaviour of hydrogel diffusion more or less limited the application of hydrogel. In this study, we initiate the theoretical kinetic study of the fast homogeneous diffusion of hydrogel under different stimuli. Based on continuum mechanics and thermodynamics, we develop the theory of the fast homogeneous diffusion of hydrogel. Using this theory, we could predict the water contend in the hydrogel as a function of time. In order to prove the robustness and universality of proposed theory, we apply it to investigate three general cases of diffusion deformation: i.e. the diffusion driven by chemical potential, the diffusion driven by temperature, and the diffusion driven by the hydraulic pressure. The quantitative prediction of the diffusion and the formulas are given in each study case. Furthermore, we conduct the corresponding experiments to validate the theory. We find that the theoretical prediction matches reasonably well with our experimental data and those available in the literature. We hope our theory could be helpful to understand the kinetic behaviour of hydrogel during diffusion, especially for the diffusion of hydrogel in the deep sea, whose diffusion can be much accelerated by the hydraulic pressure.