Hierarchical Silica Nanostructures Inspired by Diatom Algae Yield Superior Deformability, Toughness, and Strength

Abstract

A universal design paradigm in biology is the use of hierarchies, which is evident in the structure of proteins, cells, tissues, and organisms, as well as outside the material realm in the design of signaling networks in complex organs such as the brain. A fascinating example of a biological structure is that of diatoms, a microscopic mineralized algae that is mainly composed of amorphous silica, which features a hierarchical structure that ranges from the nano-to the macroscale. Here, we use the porous structure found at submicron length scales in diatom algae as a basis to study a bioinspired nanoporous material implemented in crystalline silica. We consider the mechanical performance of two nanoscale levels of hierarchy, studying an array of thin-walled foil silica structures and a hierarchical arrangement of foil elements into a porous silica mesh structure. By comparing their elastic, plastic, and failure mechanisms under tensile deformation, we elucidate the impact of hierarchies and the wall width of constituting silica foils on the mechanical properties, by carrying out a series of large-scale molecular dynamics (MD) simulations with the first principles based reactive force field ReaxFF. We find that by controlling the wall width and by increasing the level of hierarchy of the nanostructure from a foil to a mesh, it is possible to significantly enhance the mechanical response of the material, creating a highly deformable, strong, and extremely tough material that can be stretched in excess of 100 pct strain, in stark contrast to the characteristic brittle performance of bulk silica. We find that concurrent mechanisms of shearing and crack arrest lead to an enhanced toughness and are enabled through the hierarchical assembly of foil elements into a mesh structure, which could not be achieved in foil structures alone. Our results demonstrate that including higher levels of hierarchy are beneficial in improving the mechanical properties and deformability of intrinsically brittle materials. The findings reported here provide insight into general material design approaches that may enable us to transform a brittle material such as silicon or silica into a ductile, yet strong and tough material, solely through alterations of its structural arrangement at the nanoscale.

Multiscale mechanics of biological and biologically inspired materials and structures

“…In an example relevant for sea creatures such as diatom algae [26], while silicon and silica is extremely brittle in bulk, the formation of nanostructures results in great ductility and extensibility, where the specific geometry used allows for a continuum of mechanical signatures [27,28]. The realization of distinct structural designs provides a means to tune the material to achieve a great diversity of functional properties despite the use of the same building blocks.…”

Deformation Modes and Structural Response of Diatom Frustules

“…In the specific case of diatoms, the limited number of mechanical simulation studies emphasizes the need to evaluate the mechanical response of frustules at the microscale. In earlier work by Garcia et al [23], MD simulations of diatom-inspired nanoporous materials were performed to investigate the effect of hierarchical nanoporous layers under tensile deformation. Although such simulations reported interesting material design insights at the atomicscale, the MD method is known to be computationally expensive for large and complex models.…”

“…In this study, mechanics of centric diatom frustules, Coscinodiscus sp., was analyzed using FEM simulation together with independent SEM images of several characteristic deformation patterns observed in nature and mechanical test measurements. The difference of this approach versus previous simulations [23][24][25] is that the structural behaviour of diatom frustules and their response to external stimuli were investigated here at the micron scale, allowing the study of the relation between diatom morphology and mechanics in a novel and systematic fashion. The main objective was to elucidate the type of mechanical interactions that might result in these particular diatom frustules.…”

Nanomechanics of biologically inspired helical silica nanostructures

“…The field of biomimetics has already led to brighter LCD screens, more efficient solar panels, more protective body armour, and more agile robots [1][2][3]. By studying structural designs found in Nature, it may be possible to develop novel materials and devices that would otherwise have gone undiscovered [4,5]. A field that has shown extensive promise is that of nanomaterials.…”

“…Diatoms are unicellular algae with various chemical and mechanical properties that have attracted the interest of those in the field of biomimetics and nanomaterials [4,[8][9][10]. The unique properties of diatoms have been the inspiration for devices such as molecular sieves, resins, and optical coatings [11].…”