Polyamides can absorb or desorb water from or to their surrounding environment. The impact of this process is significant as water molecules lead locally to a swelling and a coupling of diffusion and deformation behavior. To model these phenomena, a strongly coupled chemo-mechanical (or diffuso-mechanical) model is required, considering both local water concentration and the viscoelastic material behavior of polyamide. In the present work, we derive and apply such a model to polyamide 6. A diffusion equation describing changes in water concentration is coupled to the balance of linear momentum in polyamide 6. The interaction between deformation and concentration is derived from thermodynamic considerations by introducing a free energy consisting of a mechanical and a chemical part. The mechanical part describes a linear viscoelastic model and includes chemical strains due to the presence of water molecules. The chemical part builds upon the theory of Flory and Huggins, that takes into account changes in enthalpy and entropy of mixing due to the interaction of polymer and water molecules. The coupling of deformation to water concentration arises due to a dependency of the water flux on the hydrostatic stress inside the polyamide. We successfully apply the derived model in Finite-Element simulations to predict the drying of polyamide 6 specimens without any coupling to mechanical loads. In addition, we reproduce experimentally obtained data from relaxation measurements, where the drying of polyamide specimens leads to an increase in relaxation modulus.

聚酰胺可以从周围环境中吸收水或将水解吸到周围环境中。这个过程的影响是显着的，因为水分子会导致局部膨胀以及扩散和变形行为的耦合。为了模拟这些现象，需要一个强耦合的化学机械（或扩散机械）模型，同时考虑局部水浓度和聚酰胺的粘弹性材料行为。在目前的工作中，我们推导了这样的模型并将其应用于聚酰胺 6。描述水浓度变化的扩散方程与聚酰胺 6 中的线性动量平衡耦合。变形和浓度之间的相互作用是通过引入热力学考虑而得出的自由能由机械部分和化学部分组成。机械部分描述了线性粘弹性模型，并包括由于水分子的存在而产生的化学应变。化学部分建立在弗洛里和哈金斯的理论基础上，该理论考虑了由于聚合物和水分子的相互作用而导致的混合焓和熵的变化。变形与水浓度的耦合是由于水通量对聚酰胺内部静水应力的依赖性而产生的。我们成功地将导出的模型应用于有限元模拟，以预测聚酰胺 6 样品的干燥，而无需与机械载荷产生任何耦合。此外，我们重现了通过松弛测量获得的实验数据，其中聚酰胺样品的干燥导致松弛模量增加。