Transparent hierarchical columnar nanocomposites

Abstract

The expertise of living organisms to combine a desirable set of mechanical and optical properties in biological tissues originates from genetically controlled formation of hierarchical architecture. By mimicking the enamel prisms consisting of nanorod clusters, we integrate high transparency and ultralow haze with enamel-like hardness, modulus, and indentation fracture toughness in hierarchical columnar nanocomposites. The aligned bundled nanorods from a seeded growth on top of single nanorods are the key building unit for combining all these properties, achieving a transmittance as high as 90% in the visible and ultralow haze of less than 1%, when the refractive index of fluorapatite matches with epoxy resin with appropriate crosslinkers. The highly transparent columnar nanocomposites are also optically anisotropic showing apparent birefringence. Compared with single nanorods, bundled nanorods as inorganic motif enable similar modulus but a 40% higher indentation fracture toughness owing to the additional stress passivation mechanism at the intra-rod interface, despite of higher inorganic contents. Better energy dissipation ability under dynamic conditions is achieved for hierarchical columnar nanocomposites because of more effective plastic energy dissipation pathway. The functional synergies achieved in this study using hierarchical design underly a general biomimetic principle for creating high-performance multifunctional materials.