Computational characterization of the structural and mechanical properties of nanoporous titania

Abstract

Nanoporous titania is one of the most commonly used biomaterials with good biocompatibility and mechanical strength. Understanding to the influence of pore structures on their performances is crucial for the design and preparation of titania-based materials. Two kinds of structural models for nanoporous titania were constructed and used to investigate the effect of pore size and/or porosity on their mechanical properties by using molecular dynamic simulations with the Matsui-Akaogi potentials. The porous structures were relaxed and their elastic constants were computed and used to evaluated their bulk, shear and Young's moduli. Overlap effect in small pores, pore size and porosity have considerable influence on computed elastic moduli. Compared to bulk rutile TiO₂, reduced mechanical moduli were predicted. Simulations on uniaxial tensile tests revealed an anisotropic stress-strain relationship and a brittle-to-ductile transition for structures with large porosities. Fracture failure was predicted for all the studied porous structures. The maximum stress decreases with pore size and porosity, while the corresponding strain decreases with pore size, but increases with porosity.

Fig. 1. Pore structures with different diameters and porosity in titania.

Fig. 2. Volume thermal expansion coefficient (β) of rutile TiO₂ at different temperatures. Experimental values are given for comparison.

Fig. 3. Volume thermal expansion coefficients (β) of the porous rutile TiO₂ structures with different pore sizes (up) and porosities (bottom).

Fig. 4. Elastic moduli of porous rutile with different pore sizes. The corresponding values of bulk rutile are presented as dotted line.

Fig. 5. Elastic moduli of porous rutile with different porosities. The corresponding values of bulk rutile are presented as dotted line.

Fig. 6. Stress–strain curves of porous rutile with different pore sizes (top) and different porosities (bottom).