Probing the effects of nanoscale architecture on the mechanical properties of periodic surfactant-templated silica/polymer composite thin film

This research investigated a diverse set of elastic properties and their relationship to the nanoscale architecture of periodic silica/polymer composite thin films.;The periodic hexagonal honeycomb-structured silica/polymer composite films were synthesized through evaporation-induced self-assembly process. The nanoscale structures of the films were determined using a combination of XRD, TEM and AFM methods. Because of the anisotropy of the nanostructure, significant differences in the tensile properties between the axes parallel and perpendicular to the film-deposition direction were observed for thin films The thin films strained in the parallel dimension exhibit a yield strain up to about 0.34 +/- 0.07%, with an average modulus of about 23 +/- 5 GPa. In the perpendicular orientation, the corresponding numbers were 0.40 +/- 0.05% and 8 +/- 1 GPa, respectively. For 100 nm thick films, the average failure strains were 3.0 +/- 0.4% and 1.6 +/- 0.5% for the parallel and perpendicular orientations, respectively with similar anisotropies observed for 200 nm thick films. These strain values are about an order of magnitude larger than those seen in typical bulk silica systems. When the film thickness was in the range of 300 to 500 nm, no anisotropies of the tensile properties were observed, and both configurations exhibited data similar to the perpendicularly oriented films Cell model and finite element analysis showed that the mechanical properties of the composite films can be attributed to the nanoscale architecture of the films.;Fracture energy release rates of composite films were calculated based on the tensile measurement results. The calculated energy release rates were 12.3 +/- 0.5 J/m2 for crack growth in the parallel direction and 6.7 +/- 0.5 J/m2 for growth in the perpendicular direction. These numbers are both significantly larger than the bulk silica value of roughly 4 J/m2, indicating the dissipative effect of the inorganic/organic interface.;The composite films produced in this study possess much larger elasticity and fracture energies compare to typical bulk silica systems, while retain relatively large Young's modulus. The coupling of these desirable properties into one material appears to arise directly from the periodic nanoscale architecture of these films, which may prove useful in applications requiring control over this interplay between a material's strength and elasticity.