Probing the effects of nanoscale architecture on the mechanical properties of hexagonal silica/polymer composite thin films

We examine the effects of controlling nanoscale architecture on the tensile properties of honeycomb-structured silica/polymer composite films. The hexagonal films are produced using evaporation-induced self-assembly and uniaxially strained using a home-built tensile testing apparatus. Significant differences in the yield strain, failure strain, and tensile moduli between the axes parallel and perpendicular to the film-deposition direction are observed for the thinnest films examined and are attributed to anisotropy in the film nanostructure that is further characterized with transmission electron microscopy and atomic force microscopy. For properly oriented composites, these films have tensile moduli comparable to the Young's modulus of bulk silica but exhibit failure strains that are about an order of magnitude larger than those seen in typical bulk-silica systems. The yielding and failure processes are explored using X-ray diffraction and optical microscopy and are characterized by irreversible changes in the nanoscale architecture. We show that tuning the nanoscale architecture can provide control over the tensile properties of composites, allowing for materials with combinations of stiffness and elasticity unachievable in the analogous bulk systems.