Nanoscale Multifunctional Materials: Nature Inspired Hierarchical Architectures

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The largest variety of efficient and elegant multifunctional materials is seen in natural biological systems, which very seldom occur in the simple geometrical shapes of traditional man-made materials. For bio-materials involved in surface-interface related processes, common geometries involve capillaries, dendrites, hair, or fin-like attachments supported on larger substrates. It may be beneficial to incorporate similar hierarchical structures in the design and fabrication of multifunctional synthetic materials that involve surface sensitive functions such as sensing, reactivity, charge storage, thermal/electrical transport or stress transfer.

If one were to select a base material for creating such structures, graphitic carbon will perhaps be the most versatile. Hexagonal sheets of sp2 carbon can have unprecedented mechanical strength, electrical and thermal conductivity within the plane, but weaker bond-strength and conductivities normal to the planes. Therefore, properties of graphene based solids can often be dictated by relative orientation of the hexagonal planes in the overall solid.

Among various grapheme-based structures, carbon nanotubes (CNT) can be suitable building blocks for the biomimetic hierarchical structures, due to their geometry and dimensions. Moreover, there is reasonable evidence in the literature1,2 that many of their electrical, thermal, mechanical and magnetic properties can be tailored though control of radius, chirality, helicity, and stacking that can, in-turn, be controlled through process parameters.