ABSTRACT
Oxide glasses are an elementary group of materials in modern society, but brittleness limits their wider usability at room temperature. As an exception to the rule, amorphous aluminum oxide (a-Al2 O3 ) is a rare diatomic glassy material exhibiting significant nanoscale plasticity at room temperature. Here, it is shown experimentally that the room temperature plasticity of a-Al2 O3 extends to the microscale and high strain rates using in situ micropillar compression. All tested a-Al2 O3 micropillars deform without fracture at up to 50% strain via a combined mechanism of viscous creep and shear band slip propagation. Large-scale molecular dynamics simulations align with the main experimental observations and verify the plasticity mechanism at the atomic scale. The experimental strain rates reach magnitudes typical for impact loading scenarios, such as hammer forging, with strain rates up to the order of 1 000 s-1 , and the total a-Al2 O3 sample volume exhibiting significant low-temperature plasticity without fracture is expanded by 5 orders of magnitude from previous observations. The discovery is consistent with the theoretical prediction that the plasticity observed in a-Al2 O3 can extend to macroscopic bulk scale and suggests that amorphous oxides show significant potential to be used as light, high-strength, and damage-tolerant engineering materials.
ABSTRACT
The glass transition temperature (Tg) of a series of polyacrylate- and polymethacrylate-based polymers having bistable hydrazone photoswitches as pendants increases upon photoisomerization. The ensuing photohardening of the polymeric network was corroborated using nanoindentation measurements. The bistability of the switch allowed us to lock-in and sustain multiple Tg values in the same polymeric material as a function of the hydrazone switch's Z/E isomer ratio, even at elevated temperatures.
