Application of a new thermodynamic model to the swelling behaviour of poly(N-isopropylacrylamide) gels in aqueous solutions of alcohols

三维交联聚n-异丙基丙烯酰胺（PNIPAM）形成非离子型和热敏型水凝胶，实验研究非常深入。在大约32°C的温度下，凝胶会从收缩状态过渡到强烈膨胀状态。由于方便的转变温度，这些水凝胶已经找到了广泛的医疗应用，包括控制药物输送系统，人造血管和肌肉以及隐形眼镜。在经典的溶胀理论中，凝胶是一种无限大的交联聚合物分子，它包裹着溶剂分子。一种基于膨胀平衡的新模型允许许多交联聚合物分子包裹不同数量的溶剂。到目前为止，该模型仅使用亥姆霍兹能量的简单表达式应用于PNIPAM在纯水中的膨胀行为。在这里，这个表达式将通过加入化学关联模型来改进。此外，该模型将扩展到两种溶剂的情况（详细说明：PNIPAM在水和酒精的混合物中的溶胀）。在这种情况下，主要目标是计算溶胀度作为温度和溶剂混合物组成的函数。

Three dimensional cross linked poly (N-isopropylacrylamide) (PNIPAM) forms non-ionic and thermo-sensitive hydrogels that have been experimentally studied very thoroughly. Cooling the gel there is a transition from a shrunken to a strongly swollen state at approximately 32°C. Because of the convenient transition temperature these hydrogels have found a wide range of medical applications, including controlled drug delivery systems, artificial blood vessels and muscles as well as contact lenses. In the classical swelling theory a gel is an infinitely large cross-linked polymer molecule that encages the solvent molecules. A new model is based on swelling equilibria and permits many cross-linked polymer molecules that encage different amounts of solvent. Until now, this model was applied only to the swelling behaviour of PNIPAM in pure water using a simple expression for the Helmholtz energy. Here, this expression is to be improved by incorporation of chemical association models. Furthermore, the model is to be extended to the case of two solvents (in detail: swelling of PNIPAM in mixtures of water and an alcohol). In this, the main goal is the calculation of the swelling degree as function of the temperature and of the composition of the solvent mixture.