Modeling the effects of temperature and pH on swelling of stimuli-responsive gels

• A model is derived for the mechanical response of thermo- and pH-sensitive gels.
• Quantitative agreement is demonstrated between observations under unconstrained swelling and results of simulation.
• The effects of temperature, pH, and concentration of ionic monomers on constrained swelling are studied numerically.

A model is developed for the mechanical behavior of and water uptake by thermo- and pH-sensitive gels. Constitutive equations are derived by means of the free energy imbalance inequality for an arbitrary three-dimensional deformation accompanied by swelling. Adjustable parameters are found by fitting experimental data on N-isopropylacrylamide–acrylic acid, N-isopropylacrylamide–itaconic acid, N-isopropylacrylamide–sodium acrylate and N-isopropylmethacrylamide–sodium methacrylate copolymer gels under unconstrained swelling. Quantitative agreement is demonstrated between the observations and results of simulation. The effects of temperature, pH, and molar fraction of anionic monomers on degree of swelling under constrained water uptake are studied numerically.

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