Farzaneh Kalourazi Saeideh, Wang Fei, Zhang Haodong, Selzer Michael, Nestler Britta
Institute of Applied Materials-Microstructure Modelling and Simulation, Karlsruhe Institute of Technology, Straße am Forum 7, Karlsruhe 76131, Germany.
Institute of Digital Materials Science, Karlsruhe University of Applied Sciences, Moltkestraße 30, Karlsruhe 76133, Germany.
J Phys Condens Matter. 2022 Sep 5;34(44). doi: 10.1088/1361-648X/ac8b4d.
The porous microstructure has been widely observed in a variety of polymer solutions that have been broadly applied in many industry fields. Phase separation is one of the common mechanisms for the formation of the porous microstructure in binary polymeric mixtures. Previous studies for the formation of porous microstructures mostly focus on the separation of the bulk phase. However, there is a paucity of investigation for the phase separation of polymer mixtures contacting the solid substrate. When the polymeric liquid mixtures interact with the solid substrate, the wetting boundary condition has to be taken into account. In this work, we present a phase-field model which is coupled with the wetting boundary condition to study the phase separation in binary polymer solutions. Our consideration is based on the polymerization-induced phase separation, and thermally induced phase separation by using the Flory-Huggins model. By taking the wetting effect into account, we find that polymer droplets spontaneously occur in the microstructure, even though the bulk composition is outside the spinodal region. This phenomenon is caused by the surface composition resulting from the wetting effect that was often overlooked in literature. For the phase separation in the binary polymer mixture, we also study the impact of the temperature gradient on the microstructural evolution. The porosity, the number of droplets, and the mean radius of the droplets are rationalized with the temperature gradient.
多孔微结构已在多种聚合物溶液中被广泛观察到，这些聚合物溶液已广泛应用于许多工业领域。相分离是二元聚合物混合物中形成多孔微结构的常见机制之一。先前关于多孔微结构形成的研究大多集中在本体相的分离上。然而，对于与固体基质接触的聚合物混合物的相分离研究较少。当聚合物液体混合物与固体基质相互作用时，必须考虑润湿边界条件。在这项工作中，我们提出了一个与润湿边界条件耦合的相场模型，以研究二元聚合物溶液中的相分离。我们的考虑基于聚合诱导相分离和使用弗洛里-哈金斯模型的热诱导相分离。通过考虑润湿效应，我们发现即使本体组成处于亚稳区之外，聚合物液滴也会在微结构中自发出现。这种现象是由润湿效应导致的表面组成引起的，而这在文献中常常被忽视。对于二元聚合物混合物中的相分离，我们还研究了温度梯度对微结构演变的影响。孔隙率、液滴数量和液滴平均半径与温度梯度具有合理的关系。
