Verho Tuukka, Karppinen Pasi, Gröschel André H, Ikkala Olli
Molecular Materials Department of Applied Physics Aalto University FI-02150 Espoo Finland.
Proto Rhino Ltd Betonimiehenkuja 5CFI-02150 Espoo Finland.
Adv Sci (Weinh). 2017 Dec 18;5(1):1700635. doi: 10.1002/advs.201700635. eCollection 2018 Jan.
Mollusk nacre is a prototypical biological inorganic-organic composite that combines high toughness, stiffness, and strength by its brick-and-mortar microstructure, which has inspired several synthetic mimics. Its remarkable fracture toughness relies on inelastic deformations at the process zone at the crack tip that dissolve stress concentrations and stop cracks. The micrometer-scale structure allows resolving the size and shape of the process zone to understand the fracture processes. However, for better scalability, nacre-mimetic nanocomposites with aligned inorganic or graphene nanosheets are extensively pursued, to avoid the packing problems of mesoscale sheets like in nacre or slow in situ biomineralization. This calls for novel methods to explore the process zone of biomimetic nanocomposites. Here the fracture of nacre and nacre-inspired clay/polymer nanocomposite is explored using laser speckle imaging that reveals the process zone even in absence of changes in optical scattering. To demonstrate the diagnostic value, compared to nacre, the nacre-inspired nanocomposite develops a process zone more abruptly with macroscopic crack deflection shown by a flattened process zone. In situ scanning electron microscopy suggests similar toughening mechanisms in nanocomposite and nacre. These new insights guide the design of nacre-inspired nanocomposites toward better mechanical properties to reach the level of synergy of their biological model.
软体动物珍珠层是一种典型的生物无机-有机复合材料，通过其砖石结构微观结构兼具高韧性、刚度和强度，这激发了多种合成模拟物的出现。其卓越的断裂韧性依赖于裂纹尖端过程区的非弹性变形，这种变形能够消除应力集中并阻止裂纹扩展。微米级结构有助于解析过程区的尺寸和形状，从而理解断裂过程。然而，为了实现更好的可扩展性，人们广泛研究具有排列有序的无机或石墨烯纳米片的仿珍珠层纳米复合材料，以避免出现像珍珠层中那样的中尺度片层堆积问题或缓慢的原位生物矿化现象。这就需要新的方法来探索仿生纳米复合材料的过程区。在此，利用激光散斑成像技术研究了珍珠层及受珍珠层启发的黏土/聚合物纳米复合材料的断裂情况，该技术即使在光学散射无变化的情况下也能揭示过程区。为了证明其诊断价值，与珍珠层相比，受珍珠层启发的纳米复合材料形成过程区的速度更快，且宏观裂纹出现偏转，过程区呈现扁平状。原位扫描电子显微镜显示纳米复合材料和珍珠层具有相似的增韧机制。这些新的见解为设计具有更好力学性能的受珍珠层启发的纳米复合材料提供了指导，使其达到其生物模型的协同水平。
