Sharma Hom N, Kroonblawd Matthew P, Sun Yunwei, Glascoe Elizabeth A
Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, California, 94550, United States.
Sci Rep. 2018 Nov 15;8(1):16889. doi: 10.1038/s41598-018-35181-1.
Moisture sorption and diffusion exacerbate hygrothermal aging and can significantly alter the chemical and mechanical properties of polymeric-based components over time. In this study, we employ a multi-pronged multi-scale approach to model and understand moisture diffusion and sorption processes in polyimide polymers. A reactive transport model with triple-mode sorption (i.e., Henry's, Langmuir, and pooling), experiments, and first principles atomistic computations were combined to synergistically explore representative systems of Kapton H and Kapton HN polymers. We find that the CaHPO processing aid used in Kapton HN increases the total moisture uptake (~0.5 wt%) relative to Kapton H. Henry's mode is found to play a major role in moisture uptake for both materials, accounting for >90% contribution to total uptake.However, the pooling mode uptake in Kapton HN was ~5 times higher than in Kapton H. First principles thermodynamics calculations based on density functional theory predict that water molecules chemisorb (with binding energy ~17-25 kcal/mol) on CaHPO crystal surfaces. We identify significant anisotropy in surface binding affinity, suggesting a possible route to tune and mitigate moisture uptake in Kapton-based systems through controlled crystal growth favoring exposure of CaHPO (101) surfaces during manufacturing.
水分吸附和扩散会加剧湿热老化，并会随着时间的推移显著改变聚合物基部件的化学和机械性能。在本研究中，我们采用多管齐下的多尺度方法来模拟和理解聚酰亚胺聚合物中的水分扩散和吸附过程。将具有三模态吸附（即亨利吸附、朗缪尔吸附和聚集吸附）的反应传输模型、实验以及第一性原理原子计算相结合，协同探索Kapton H和Kapton HN聚合物的代表性体系。我们发现，与Kapton H相比，Kapton HN中使用的CaHPO加工助剂会增加总吸水量（约0.5 wt%）。发现亨利吸附模式在两种材料的水分吸收中起主要作用，对总吸水量的贡献超过90%。然而，Kapton HN中的聚集吸附模式吸水量比Kapton H高约5倍。基于密度泛函理论的第一性原理热力学计算预测，水分子在CaHPO晶体表面发生化学吸附（结合能约为17 - 25 kcal/mol）。我们确定了表面结合亲和力存在显著的各向异性，这表明在制造过程中通过控制晶体生长以利于CaHPO(101)表面暴露，有可能调整和减轻Kapton基体系中的水分吸收。
