Wang Jie, Adami Daniel, Lu Bo, Liu Chuntai, Maazouz Abderrahim, Lamnawar Khalid
Key Laboratory of Materials Processing and Mold (Ministry of Education), National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China.
CNRS, UMR 5223, Ingénierie des Matériaux Polymères, INSA Lyon, Université de Lyon, F-69621 Villeurbanne, France.
Polymers (Basel). 2020 Nov 5;12(11):2596. doi: 10.3390/polym12112596.
An understanding of the structural evolution in micro-/nano-layer co-extrusion process is essential to fabricate high-performance multilayered products. Therefore, in this work, we reveal systematically the multiscale structural development, involving both the layer architecture and microstructure within layers of micro-/nano-layer coextruded polymer films, as well as its relationship to dielectric properties, based on poly(vinylidene fluoride--hexafluoropropylene) (PVDF-HFP)/polycarbonate (PC) system. Interestingly, layer architecture and morphology show strong dependences on the nominal layer thicknesses. Particularly, with layer thickness reduced to nanometer scale, interfacial instabilities triggered by viscoelastic differences between components emerge with the creation of micro-droplets and micro-sheets. Films show an enhanced crystallization with the formation of two-dimensional (2D) spherulites in microlayer coextruded systems and the oriented in-plane lamellae in nanolayer coextruded counterparts, where layer breakup in the thinner layers further changes the crystallization behaviors. These macro- and microscopic structures, developed from the co-extrusion process, substantially influence the dielectric properties of coextruded films. Mechanism responsible for dielectric performance is further proposed by considering these effects of multiscale structure on the dipole switching and charge hopping in the multilayered structures. This work clearly demonstrates how the multiscale structural evolution during the micro-/nano-layer coextrusion process can control the dielectric properties of multilayered products.
了解微/纳层共挤出过程中的结构演变对于制造高性能多层产品至关重要。因此，在本工作中，我们基于聚偏氟乙烯-六氟丙烯（PVDF-HFP）/聚碳酸酯（PC）体系，系统地揭示了微/纳层共挤出聚合物薄膜各层内的层结构和微观结构的多尺度结构发展，以及其与介电性能的关系。有趣的是，层结构和形态对名义层厚度有很强的依赖性。特别是，当层厚度减小到纳米尺度时，由于组分间粘弹性差异引发的界面不稳定性会伴随着微滴和微片的产生而出现。在微层共挤出体系中，薄膜表现出增强的结晶作用，形成二维（2D）球晶；在纳层共挤出体系中，则形成面内取向的片晶，其中较薄层中的层破裂进一步改变了结晶行为。由共挤出过程形成的这些宏观和微观结构，极大地影响了共挤出薄膜的介电性能。通过考虑多尺度结构对多层结构中偶极子开关和电荷跳跃的这些影响，进一步提出了介电性能的作用机制。这项工作清楚地展示了微/纳层共挤出过程中的多尺度结构演变如何能够控制多层产品的介电性能。
