Towards a better understanding of the interdiffusion behavior of solution-processed polymer multilayers during drying

对于溶液处理的聚合物多层应用，不同层之间的相互作用对产品质量起着决定性的作用。对于聚合物多层膜的生产，单独的聚合物要么被熔化和挤压，要么被溶解在合适的溶剂中，并作为“湿膜”应用，因此在随后的干燥步骤中必须去除该溶剂。在湿法薄膜加工过程中，溶剂会溶解下垫层，导致层间聚合物相互扩散。根据应用的不同，层间互扩散是一种理想的现象，或者应该避免。例如，对于有机发光二极管，必须防止不同功能层之间的相互扩散，以确保器件功能。在添加剂制造领域，添加溶剂可以起到增塑剂的作用，从而能够加工具有较高玻璃化转变温度的聚合物。在这种背景下，溶剂挥发过程中的层间互扩散对层层3D打印结构的粘合起着重要的作用。在聚合物-溶剂体系和聚合物熔体中的扩散过程以及聚合物-多溶剂体系的干燥过程中，已经进行了一些出色的理论和实验研究。到目前为止，聚合物在薄膜干燥过程中溶液处理的多层膜中的互扩散还不是研究的主题。干燥动力学对于预测互扩散行为是非常重要的，因为聚合物的流动性强烈地依赖于薄膜中的溶剂含量。就我们所知，文献中还没有关于这一主题的相关工作发表。通过拟议的研究项目，我们的目标是缩小这一差距，并对聚合物双层中的质量传输过程有一个基本的了解，以便预测和控制在特定干燥条件下聚合物-聚合物-溶剂体系的相互扩散。这些研究将为今后聚合物多层膜的生产工艺提供宝贵的工具。

For solution-processed polymer multilayer applications, the interaction between the different layers is decisive for the product quality. For the production of polymer multilayers, the individual polymers are either melted and extruded or dissolved in a suitable solvent and applied as a "wet film", whereby the solvent has to be removed in a subsequent drying step. During wet film processing, the solvent can dissolve the subjacent layer and cause polymer interdiffusion between the layers. Depending on the application, layer interdiffusion is a desired phenomenon or should be avoided. For example, for organic light emitting diodes, it is essential to prevent an interdiffusion between the different functional layers to ensure device functionality. In the field of additive manufacturing, the addition of solvent can act as a plasticizer and thus enable processing of polymers with a high glass transition temperature. In this context, the interdiffusion between the layers during solvent evaporation is desired as it plays a major role for the adhesion of the layer-by-layer 3D printed structures.Some excellent theoretical and experimental research has been performed on diffusion processes in polymer-solvent systems and polymer melts, as well as on the drying of polymer-multi-solvent systems. Polymer interdiffusion in solution-processed multilayers during film drying has not been the subject of research efforts so far. The drying kinetics will be of great importance for the prediction of the interdiffusion behavior, since polymer mobility is strongly dependent on the solvent content of the film. To the best of our knowledge, no relevant work has been published on this subject in the literature.With the proposed research project, we aim to close this gap and to develop a fundamental understanding of mass transport processes in polymer double-layers in order to predict and control the interdiffusion of polymer-polymer-solvent systems under defined drying conditions. The investigations will provide an invaluable tool for the production process of polymer multilayer applications in the future.