Mapping the Mechanical Properties of Hierarchical Supercrystalline Ceramic-Organic Nanocomposites.

Büsra Bor,Tobias Vossmeyer,Horst Weller,Michael Kampferbeck,Gerold A Schneider,Lydia Heilmann,Berta Domènech,Diletta Giuntini

doi:10.3390/molecules25204790

Büsra Bor, Tobias Vossmeyer + Show 6 more

Open Access

https://doi.org/10.3390/molecules25204790

Copy DOI

Abstract

Multiscale ceramic-organic supercrystalline nanocomposites with two levels of hierarchy have been developed via self-assembly with tailored content of the organic phase. These nanocomposites consist of organically functionalized ceramic nanoparticles forming supercrystalline micron-sized grains, which are in turn embedded in an organic-rich matrix. By applying an additional heat treatment step at mild temperatures (250–350 °C), the mechanical properties of the hierarchical nanocomposites are here enhanced. The heat treatment leads to partial removal and crosslinking of the organic phase, minimizing the volume occupied by the nanocomposites’ soft phase and triggering the formation of covalent bonds through the organic ligands interfacing the ceramic nanoparticles. Elastic modulus and hardness up to 45 and 2.5 GPa are attained, while the hierarchical microstructure is preserved. The presence of an organic phase between the supercrystalline grains provides a toughening effect, by curbing indentation-induced cracks. A mapping of the nanocomposites’ mechanical properties reveals the presence of multiple microstructural features and how they evolve with heat treatment temperature. A comparison with non-hierarchical, homogeneous supercrystalline nanocomposites with lower organic content confirms how the hierarchy-inducing organic excess results in toughening, while maintaining the beneficial effects of crosslinking on the materials’ stiffness and hardness.

Highlights

Bioinspiration has become a broad independent field of materials science
After pressing the self-assembled materials uniaxially in a rigid die to form bulk pellets [19,29,30], crosslinking of the organic phase is induced via heat treatment in inert atmosphere
Samples are studied before heat treatment, and after heat treatment (HT)

Summary

Introduction

Bioinspiration has become a broad independent field of materials science. After decades of breakthroughs in the characterization of biological materials, many lessons have been learnt from nature on how to design materials with exceptional combinations of properties—structural, functional, adaptable and responsive to external stimuli [1,2]. Even if consisting of a surprisingly low variety of constituents, biological materials succeed in achieving excellent properties thanks to very sophisticated designs, which optimize the content and distribution of the different phases in function of the required application [2]. When it comes to mechanical behavior, it has emerged that decisive design principles are the presence of at least two phases—a strong, hard one and a softer, more compliant one—and their organization into a hierarchical structure, namely characterized by distinctive features at each of the multiple scales it encompasses (from the macro- down to the sub-nanoscale). The majority of the volume is occupied by the stronger phase, while the compliant one forms a thin interface and serves as mortar, providing fracture toughness at the expenses of some hardness and stiffness [8]

Objectives

Methods

Results

Conclusion