Centre for Research on Adaptive Nanostructures and Nanodevices (CRANN) & School of Physics, Trinity College Dublin, Dublin 2, Ireland.
Nanoscale. 2013 Jan 21;5(2):581-7. doi: 10.1039/c2nr33049k. Epub 2012 Dec 3.
We have exfoliated hexagonal boron nitride by ultrasonication in solutions of polyvinylalcohol in water. The resultant nanosheets are sterically stabilised by adsorbed polymer chains. Centrifugation-based size-selection was used to give dispersions of nanosheets with aspect ratio (length/thickness) of ∼1400. Such dispersions can be used to produce polyvinylalcohol-BN composite films. Helium ion microscopy of fracture surfaces shows the nanosheets to be well dispersed and the composites to fail by pull-out. We find both modulus, Y, and strength, σ(B), of these composites to increase linearly with volume fraction, V(f), up to V(f)∼ 0.1 vol% BN before falling off. The rates of increase are extremely high; dY/dV(f) = 670 GPa and dσ(B)/dV(f) = 47 GPa. The former value matches theory based on continuum mechanics while the latter value is consistent with remarkably high polymer-filler interfacial strength. However, because the mechanical properties increase over such a narrow volume fraction range, the maximum values of both modulus and strength are only ∼40% higher than the pure polymer. This phenomenon has also been observed for graphene-filled composites and represents a serious hurdle to the production of high performance polymer-nanosheet composites.
我们通过在聚乙烯醇水溶液中超声剥离六方氮化硼。所得纳米片通过吸附的聚合物链稳定。基于离心的尺寸选择用于提供具有纵横比（长度/厚度）约 1400 的纳米片分散体。这种分散体可用于制备聚乙烯醇-BN 复合材料薄膜。断口的氦离子显微镜表明纳米片分散良好，复合材料通过拔出而失效。我们发现这些复合材料的模量 Y 和强度 σ（B）都随体积分数 V（f）线性增加，直到 V（f）约为 0.1 体积% BN 之前才下降。增加的速率非常高；dY/dV（f）= 670 GPa 和 dσ（B）/dV（f）= 47 GPa。前者值基于连续介质力学理论，而后者值与聚合物-填料界面强度非常高一致。然而，由于机械性能在如此窄的体积分数范围内增加，模量和强度的最大值仅比纯聚合物高约 40%。这种现象也在石墨烯填充复合材料中观察到，这是制备高性能聚合物-纳米片复合材料的严重障碍。
