Sacrificial Bonds in Stacked-Cup Carbon Nanofibers: Biomimetic Toughening Mechanisms for Composite Systems
Sacrificial Bonds in Stacked-Cup Carbon Nanofibers: Biomimetic Toughening Mechanisms for Composite Systems
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DOI：
10.1021/nn100661a
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发表时间：
2010-07-01
期刊：
影响因子：
17.1
通讯作者：
Brinson, L. Catherine
中科院分区：
文献类型：
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作者：
Palmeri, Marc J.;Putz, Karl W.;Brinson, L. Catherine
许多天然复合材料，如珍珠层或骨，通过有机相中链段之间非共价二级键的断裂来实现特殊的增韧增强。这种“牺牲键”断裂耗散了大量的能量，并由于高度卷曲的大分子的解开而显示出显著的隐藏长度，从而使其共价骨架的结构完整性保持完整以进行大的延伸。在这项工作中，我们提出了类似的牺牲键机制的第一个证据，在无机相的复合材料使用廉价的叠杯碳纳米纤维（CNF），这是由螺旋盘绕的石墨烯片与相邻层之间的石墨间距。这些CNF分散在一系列含有三官能和四官能树脂的高性能环氧体系中，这些树脂传统上难以根据其高度交联的网络增韧。尽管如此，对于各种共混物，仅添加0.68重量%的CNF产生43-112%的韧性增强。相关的增韧机制的分析揭示了两个迄今未见的机制，使用牺牲债券，补充观察到的裂纹偏转，断裂，脱粘/拔出，是常见的许多复合材料系统。首先，嵌入的纳米纤维可以在侧壁中的相邻石墨层之间离散地张开;其次，裂纹桥接纳米纤维可以连续地解开。这两种机制都需要侧壁中的层之间的π-π相互作用的耗散，而不损害石墨烯片的结构完整性。此外，发现电导率增加了7-10个数量级，突出了CNF作为增强材料的多功能性，用于设计具有改善的电性能的坚韧、廉价的纳米复合材料。
Many natural composites, such as nacre or bone, achieve exceptional toughening enhancements through the rupture of noncovalent secondary bonds between chain segments in the organic phase. This "sacrificial bond" rupture dissipates enormous amounts of energy and reveals significant hidden lengths due to unraveling of the highly coiled macromolecules, leaving the structural integrity of their covalent backbones intact to large extensions. In this work, we present the first evidence of similar sacrificial bond mechanisms in the inorganic phase of composites using inexpensive stacked-cup carbon nanofibers (CNF), which are composed of helically coiled graphene sheets with graphitic spacing between adjacent layers. These CNFs are dispersed in a series of high-performance epoxy systems containing trifunctional and tetrafunctional resins, which are traditionally difficult to toughen in light of their highly cross-linked networks. Nonetheless, the addition of only 0.68 wt % CNF yields toughness enhancements of 43-112% for the various blends. Analysis of the relevant toughening mechanisms reveals two heretofore unseen mechanisms using sacrificial bonds that complement the observed crack deflection, rupture, and debonding/pullout that are common to many composite systems. First, embedded nanofibers can splay discretely between adjacent graphitic layers in the side walls; second, crack-bridging nanofibers can unravel continuously. Both of these mechanisms entail the dissipation of the pi-pi interactions between layers in the side walls without compromising the structural integrity of the graphene sheets. Moreover, increases in electrical conductivity of similar to 7-10 orders of magnitude were found, highlighting the multifunctionality of CNFs as reinforcements for the design of tough, inexpensive nanocomposites with improved electrical properties.