Nanomechanics of biologically inspired helical silica nanostructures

Abstract

Diatoms are unicellular algae that exhibit highly intricate, silicified cell walls called frustules. Frustules consist of hierarchical nanostructures composed of amorphous silica and organic protein. Earlier work has suggested diatoms as inspiration for novel molecular sieves, resins, and optical coatings because of their unique mechanical, structural, and optical properties. Here the present authors report studies of the mechanics of helical silica structures inspired by the geometry found in diatom frustules consisting of both crystalline and amorphous silica. Molecular dynamics simulations are reported with the reactive force field ReaxFF, which is a powerful model to describe interatomic interactions derived directly from first principles quantum mechanics. It is found that introducing a helical nanostructural geometry gives the typically brittle silica a highly ductile, yet softer, mechanical behaviour: extensions of 100 per cent to roughly 300 per cent are observed for varying helical geometries. The present authors show that hydroxide termination markedly affects the mechanical properties of the silica, lowering both the Young’s modulus and the ultimate strength of the structures. The results reported here demonstrate the potential to drastically alter, and possibly improve, the properties of an inherently brittle material by confining structural features to the nanoscale and by altering its hierarchical geometry without introducing any additional material components, solely relying on geometrical changes.