Mechanical Properties of Nanoparticles and Nanotubes with Continuous Ceramic Coatings and Cross-Links

The deposition of continuous ceramic coatings on nanoparticles (NPs) or introducing covalent cross-links between carbon nanotubes (CNTs) can strongly improve the mechanical properties of the porous nanocomposite. The continuous coating specifically acts as a binding agent that promotes the mechanical integrity of a nano-powder and transforms it into a porous nanocomposite. This dissertation quantifies the effect of continuous coating on the mechanical properties of individual NPs, and cross-links on the mechanical properties of CNTs as well as their nanocomposite structures using atomistic simulations. The simulations of quasi-static compression of single-material SiC NPs showed that 6H-SiC NPs demonstrate stronger resistance to compression compared to 3C-SiC NPs with the dominant mechanism of deformation dependent on the type of the SiC polymorph, NP size, temperature, and lattice orientation. For impact interaction between SiC NPs, coefficients of restitution as functions of the NP size, impact parameters, and impact velocity are determined based on results of atomistic simulations. Simulations of linear arrays composed of core-shell Si/SiC NPs reveal dramatic differences in the dominant mechanisms of inelastic deformation, mechanical properties, and phase changes between the arrays with and without continuous coating (overlap of ceramic shells). Overall, the continuous SiC coating on Si NPs can increase the material modulus and strength in up to 1.5 orders of magnitude, turning a nano-powder into a porous nanomaterial with excellent mechanical properties. The simulations of Si NPs arranged in a face centered cubic structure with continuous 6H-SiC coating showed that a 1 nm thick coating induces a dramatic order-of-magnitude increase in the elastic modulus of a pure Si nano-powder while a further increase in thickness results in a significant increase in 12-fold over a Si nano-powder. A combined atomistic-mesoscopic study performed to reveal the effect of CNT radius on the deformation mechanisms and mechanical properties of low-density CNT films with covalent cross-links showed that the mechanical properties of CNT films are found to be strongly dependent on the CNT radius while the stretching rigidity of individual nanotubes and volumetric CL density are identified as the key factors that dominate the effect of CNT chirality on mechanical properties of CNT films.