Modeling the free swelling of a photo-thermal-pH triple-responsive polyampholytic hydrogel loaded with Au nanoparticles under photothermal conversion and chemical reactions

Photo-thermal-pH triple stimuli-responsive polyampholytic hydrogels containing light-absorbing Au nanoparticles, anionic and cationic functional groups along main and side chains possess better salt sensitivity compared to purely anionic or cationic hydrogels under certain conditions, which are sensitive to changes in temperature, pH and light intensity. In this paper, a continuum theory for photo-thermal-pH triple stimuli-responsive polyampholytic hydrogels is developed, with the consideration of the coupling between large deformation, photothermal conversion and chemical reactions. The comparison between the predicted results of a stress-free swelling example with the corresponding experimental data in the literature indicates that the proposed model is applicable to free swelling of the photo-thermal-pH triple-responsive polyampholytic hydrogels. Based on the proposed model, the influence of temperature, pH and light intensity, as well as functional groups’ concentration on the swelling ratio of the hydrogels is then analyzed. In addition, the model is extended to study the inhomogeneous and anisotropic swelling of a core-shell structure, with an exterior photo-thermal-pH triple responsive polyampholytic hydrogel and an interior hard core.