Wang Can, Kilic Karsu I, Koerner Hilmar, Baur Jeffery W, Varshney Vikas, Lionti Krystelle, Dauskardt Reinhold H
Department of Chemistry, Stanford University, 364 Lomita Drive, Stanford, California 94305, United States.
Department of Materials Science and Engineering, Stanford University, 496 Lomita Mall, Stanford, California 94305, United States.
ACS Appl Mater Interfaces. 2022 Jun 22;14(24):28239-28246. doi: 10.1021/acsami.2c02575. Epub 2022 Jun 9.
Polyimide hybrid nanocomposites with the polyimide confined at molecular length scales exhibit enhanced fracture resistance with excellent thermal-oxidative stability at low density. Previously, polyimide nanocomposites were fabricated by infiltration of a polyimide precursor into a nanoporous matrix followed by sequential thermally induced imidization and cross-linking of the polyimide under nanometer-scale confinement. However, byproducts formed during imidization became volatile at the cross-linking temperature, limiting the polymer fill level and degrading the nanocomposite fracture resistance. This is solved in the present work with an easier approach where the nanoporous matrix is filled with shorter preimidized polyimide chains that are cross-linked while in the pores to eliminate the need for confined imidization reactions, which produces better results compared to the previous study. In addition, we selected a preimidized polyimide that has a higher chain mobility and a stronger interaction with the matrix pore surface. Consequently, the toughness achieved with un-cross-linked preimidized polyimide chains in this work is equivalent to that achieved with the cross-linking of the previously used polyimide chains and is doubled when preimidized polyimide chains are cross-linked. The increased chain mobility enables more efficient polymer filling and higher polymer fill levels. The higher polymer-pore surface interaction increases the energy dissipation during polyimide molecular bridging, increasing the nanocomposite fracture resistance. The combination of the higher polymer fill and the stronger polymer-surface interaction is shown to provide significant improvements to the nanocomposite fracture resistance and is validated with a molecular bridging model.
在分子长度尺度上受限的聚酰亚胺杂化纳米复合材料在低密度下具有增强的抗断裂性和优异的热氧化稳定性。此前，聚酰亚胺纳米复合材料是通过将聚酰亚胺前体渗入纳米多孔基质中，然后在纳米尺度限制下依次进行热诱导酰亚胺化和聚酰亚胺交联来制备的。然而，酰亚胺化过程中形成的副产物在交联温度下会挥发，限制了聚合物填充水平并降低了纳米复合材料的抗断裂性。在本工作中，通过一种更简便的方法解决了这一问题，即纳米多孔基质填充较短的预酰亚胺化聚酰亚胺链，这些链在孔中交联，从而无需受限的酰亚胺化反应，与先前的研究相比，产生了更好的结果。此外，我们选择了一种具有更高链迁移率且与基质孔表面相互作用更强的预酰亚胺化聚酰亚胺。因此，本工作中未交联的预酰亚胺化聚酰亚胺链所实现的韧性与先前使用的聚酰亚胺链交联所实现的韧性相当，而当预酰亚胺化聚酰亚胺链交联时，韧性会翻倍。链迁移率的提高使聚合物填充更高效且聚合物填充水平更高。更高的聚合物 - 孔表面相互作用增加了聚酰亚胺分子桥接过程中的能量耗散，提高了纳米复合材料的抗断裂性。更高的聚合物填充和更强的聚合物 - 表面相互作用的结合被证明能显著提高纳米复合材料的抗断裂性，并通过分子桥接模型得到验证。
