TC06: Mechanical Behavior at the Micro and Nanoscale—Bridging Between Computer Simulations and Experiments
Sung Hoon Hwang, Rice University
Intrinsic and Pseudo Size-Effect in Scaffolded Porous Nanoparticles and Their Self-Assembled Ensembles
Written by Hortense Le Ferrand
The mechanical properties of porous nanoparticles can dictate their application. For example, too soft nanoparticles will be trapped at the surface of body tissues and thus cannot be used as drug carriers.
As a model system, Sung Hoon Hwang and his colleagues used calcium-silicate monodisperse porous nanoparticles featuring 3 nm pores and various diameter sizes, from 173 nm to 524 nm. Apply a force on a single nanoparticle with a flat tip of a nanoindenter, the increase in diameter of the particles reflects a brittle-to-ductile transition. Indeed, nanoparticles of 290 nm diameter have a Young modulus of 14 GPa and a toughness of 30 MJ/m3, while larger particles of 520 nm have a lower modulus of 6 GPa but a higher toughness of 60 MJ/m3. Interestingly, close-packed self-assembled films of these particles did not exhibit any size-dependency: The Young’s modulus plateaus for all sizes at around 40 GPa. However, fracture surfaces differed in morphology between thicker and thinner regions, where radial cracks dominate in the first case whereas particle pile-up occurs in the later case. In compacted bodies, corresponding to thicker layers of particles, not necessarily close packed, the modulus showed also independence to the particle size, but at a value of only 10 GPa similar to that of individual nanoparticles.
Beyond the numerical values, nanoindentation of single or assemblies of nanoparticles highlight the importance of particle interactions and packing to enhance the mechanical properties.