Abstract：
Polymer fibers that combine high toughness and heat resistance are hard to achieve, which, however, hold tremendous promise in demanding applications such as aerospace and military. This prohibitive design task exists due to the opposing property dependencies on chain dynamics because traditional heat-resistant materials with rigid molecular structures typically lack the mechanism of energy dissipation. Aramid nanofibers have received great attention as high-performance nanoscale building units due to their intriguing mechanical and thermal properties, but their distinct structural features are yet to be fully captured. We show that aramid nanofibers form nanoscale crimps during the removal of water, which primarily resides at the defect planes of pleated sheets, where the folding can occur. The precise control of such a structural relaxation can be realized by exerting axial loadings on hydrogel fibers, which allows the emergence of aramid fibers with varying angles of crimps. These crimped fibers integrate high toughness with heat resistance, thanks to the extensible nature of nanoscale crimps with rigid molecular structures of poly(p-phenylene terephthalamide), promising as a template for stable stretchable electronics. The tensile strength/modulus (392-944 MPa/11-29 GPa), stretchability (25-163%), and toughness (154-445 MJ/cm3) are achieved according to the degree of crimping. Intriguingly, a toughness of around 430 MJ/m3 can be maintained after calcination below the relaxation temperature (259 °C) for 50 h. Even after calcination at 300 °C for 10 h, a toughness of 310 MJ/m3 is kept, outperforming existing polymer materials. Our multiscale design strategy based on water-bearing aramid nanofibers provides a potent pathway for tackling the challenge for achieving conflicting property combinations.
摘要：
兼具高韧性和耐热性的聚合物纤维很难实现，which,然而,在航空航天和军事等苛刻的应用中拥有巨大的希望。由于具有刚性分子结构的传统耐热材料通常缺乏能量耗散机制，因此存在这种禁止性设计任务。芳纶纳米纤维作为高性能的纳米级建筑单元，由于其耐人寻味的机械和热性能而受到了极大的关注，但是它们独特的结构特征尚未被完全捕获。我们表明芳纶纳米纤维在去除水的过程中会形成纳米级的卷曲，主要存在于褶板的缺陷平面上，可以发生折叠的地方。这种结构松弛的精确控制可以通过在水凝胶纤维上施加轴向载荷来实现。这允许出现具有不同卷曲角度的芳族聚酰胺纤维。这些卷曲纤维具有高韧性和耐热性，由于具有刚性分子结构的聚（对苯二甲酰对苯二胺）的纳米级卷曲的可延伸性质，有希望作为稳定的可拉伸电子设备的模板。抗拉强度/模量（392-944MPa/11-29GPa），拉伸性（25-163%），和韧性(154-445MJ/cm3)根据卷曲程度来实现。有趣的是，在低于松弛温度（259°C）煅烧50小时后，可以保持约430MJ/m3的韧性。即使在300°C煅烧10小时后，保持310MJ/m3的韧性，优于现有的聚合物材料。我们基于含水芳族聚酰胺纳米纤维的多尺度设计策略为解决实现相互矛盾的特性组合的挑战提供了有效的途径。
