Superior biomimetic nacreous bulk nanocomposites by a multiscale soft-rigid dual-network interfacial design strategy, Chen, Gao, et al., Yu, Matter, 2019
Novelty/impact/significance:
A multiscale soft-rigid dual-network interfacial design strategy produces nacre-like bulk composites with superior mechanical properties, improved stabilities in high humidity and temperature, and the process is a facile, efficient, and scalable fabrication.
Scientific question:
How to mimic and control the micro- and nano-interface layout of nacre to fabricate high-performance, bulk nacreous composites?
Organizing nanoscale reinforcements/building blocks into bulk composites with efficiency and low environmental impact for mass production is challenging.
Key of how:
A new design consists of (1) multi-scale interface of nano- and micro-scales and (2) reinforced interface by ingeniously introducing a rigid polymer into common soft organic glue (montmorillonite (MTM) nanoplatelets glued by soft polyvinyl alcohol (PVA) and stiff resol), both being interlaced.
Nanoscale interface: hydrogen bonding and physical entanglement between both polymers, and hydrogen and Al-O-C bondings between MTM and the polymers. Microscale film-film interface: the same one extended from the nanoscale interface, but larger and stiffer after thermal curing of resol. Both interfaces can be precisely manipulated for simultaneously improved/optimized mechanical properties.
Major points (useful info):
1. The nacreous ‘brick and mortar’ (B&M) structure with intricate interface has been mimicked using ceramic reinforcements to obtain high-performance composites via various methods. Many fabrications for 3D bulk composites usually need micron reinforcements and energy-intensive/complicated.
2. One key difficulty is to achieve the micro- and nano-interface layout between nano-reinforcements, with control and robustness through a simple, mild, and eco-friendly processing.
3. A multiscale soft-rigid polymer dual-network (SRPDN) interfacial design can address the above: MTM nanoplatelets, PVA, resol dispersion → by evaporation-induced self-assembly to form nanocomposite films → by stacking + hot pressing to form bulk composites.
4. The SRPDN produces nanoscale MTM-MTM interface (bondings between the interfacial polymers and those between the interfacial polymer and MTM) and microscale film-film interface, which are stiffened after hot-pressing.
5. Introducing rigid resol into the interfaces, binary MTM-PVA versus ternary MTM-PVA-resol, significantly increases strength and modulus, in both 2D films (tensile) and nanocomposites (flexural). An appropriate amount of resol is determined to acquire strengthening while avoiding brittleness. The ternary MTM-PVA-resol nacre-like nanocomposites show superior properties that other reported nacreous composites.
6. Due to the moisture-insensitivity and resistance to heat of resol, the as-prepared composites show favorable hydration- and thermal stability.
7. This SRPDN is transferrable into making nacreous, layered composites based other nanoplatelets, e.g., GO-PVA-resol.
8. FEM studies of the brick and mortar structure (of nacre) reveal that the mechanical performance of the interface modulates/controls the overall mechanical properties, and the toughening are the interface cracks. The as-prepared nacreous composites show similar toughening mechanisms (microcracking, crack deflection, bridging) as those of other natural and artificial composites.
9. The synergy of the soft and rigid polymer network plus multi-scale feature endow mechanical reinforcement and toughening mechanisms, while also have low density.
This presents a novel, simple but effective method with potential for large-scale engineering application, a forward step in the field of creating nacre-like, high-performance composites.
It is suggested to add some discussion on the efficiency of the fabrication, e.g., material property v.s. required time, and comparisons with other relevant manufacturing (if I did not miss any information), as high-efficiency has been stated multiple times in the article and this discussion should be new and important for the overall related literature.
Here is the link of the full text:
https://www.sciencedirect.com/science/article/pii/S2590238519300165#mmc1