Synthesis and toughening behavior of bio-inspired nanocrystalline TiO2/polyelectrolyte nanolayered composites

Bio-inspired (nanocrystalline TiO2/polyelectrolyte (PE))4 nanolayered composites were synthesized by the layer-by-layer self-assembly and chemical bath deposition methods. The results show that the thicknesses of the TiO2 and PE layers in the as-synthesized are 41.3 nm and 9.6 nm, respectively, and the grain size of the TiO2 layer is about 5 nm. For the type I cracking, the fracture toughness (KIC = 1.18 ± 0.67 MPa m1/2) of 41.3 nm TiO2/9.6 nm PE composite is larger than that of the bulk TiO2. For the type II cracking, the crack deflection occurred in the composite. This toughening behavior was attributed to the low interfacial fracture energy and the large ratio of the crack deflection length to the crack penetration length. Our finding demonstrates that the crack deflection is an effective way to toughen the bio-inspired nanocrystalline TiO2/PE nanolayered composites.