A lattice model for thermally-sensitive core–shell hydrogels

• A thermodynamic model for thermally-sensitive core–shell gels is developed.
• The swelling rates of two kinds of core–shell gels are calculated.
• These gels show restricted swelling behaviors.
• Their swelling ratios were controlled by the cross-linking degree and Rcore/Rshell.

A lattice molecular thermodynamic model for describing the swelling behavior of thermally-sensitive core–shell hydrogels was developed by integrating a close-packed lattice model for mixing free energy and a Flory Gaussian chain model for the elastic free energy. The thermodynamic model is characterized with two parameters: the temperature-dependent exchange energy parameter ε and the Topology-dependent size parameter V*. The input values of both parameters can be obtained by experimental results of pure polymer hydrogels. With the help of proposed model, swelling behaviors of two kinds of hydrogel systems were analyzed: one is a doubly thermally-sensitive core–shell hydrogels (with two LCSTs) and the other comprises a thermally-sensitive hydrogel shell with a hard internal core. We show that the calculated results are in good agreement with the experimental data.

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