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Layered nanocomposites by shear-flow-induced alignment of nanosheets, Chuangqi Zhao, Lei Jiang, Mingjie Liu, Nature, 2020

 

Good papers clearly state their novelty/significance, scientific question, and key of how in the abstract, and the writing is clear and coherent, despite the depth and complexity of the work.

 

Novelty/impact/significance:

A generalizable and scalable, continuous fabrication of ultrastrong composite films (with nanosheets of graphene oxide and clay, strength 1215 MPa modulus 198.8 GPa,, and ultrastrong and ultratough composites (with nanosheets of clay, toughness 36.7 MJ/m2 strength 1195 MPa) based on a superspreading layering strategy.

  

Scientific question:

How to produce ultrastrong and ultratough layered nanocomposites in a universal, viable and scalable manner?

 

Key of how:

Using shear-flow-induced alignment of nanosheets in a solution superspreading at an immiscible hydrogel/oil interface, thus producing composite films with highly aligned and ordered nano-reinforcements.

 

Major points (useful info):

1. A flowing solution (with nanofillers inside) can rapidly and completely spread at an interface of liquids to obtain a layer that later becomes a composite film, during which the nanofillers are well-aligned by shear flow force, a superspreading layering strategy.

2. The process: A circulating hydrogel layer first immerses in a lower bath to acquire Ca2+. Then it goes into an oil bath where solution containing GO nanosheets and NaAlg from arrayed syringes and forms a superspreading layer at the hydrogel/oil interface. Meanwhile, the superspreading layer is converted into a calcium alginate (CA) hydrogel film so that the aligned nano-reinforcements are fixed. This film can be readily separated by a water bath immersion. Then after heating, composite films with aligned GO/CA are obtained.

3. A strong shear flow force by the superspreading process accounts for the nanosheets’ alignment. A quantitative analysis shows that height-averaged flow velocity and shear rate are higher at the contact line, and a rapid fixation by Ca2+ crosslinking is needed.

4. The distance between syringes for forming continuous and uniform superspreading layer is crucial in terms of allowing each droplet to superspread and opportune capillary forces to coalesce for superspreading.

5. TEM, SAXS verified the highly ordered arrangement of nano-reinforcements, the rapid alignment and fixation by using dilute reaction solutions without aggregation.

6. The superspreading strategy is generalizable and scalable for continuous fabrication, extending to clay/CA nanocomposite films and compatible with thermal, photo-initiated polymerization.

7. Introducing other nanofillers (carbon nanotubes (CNTs) and PVA) into the GO/NaAlg solution enhances the mechanical properties (need to optimize the percentage of nanofillers GO, clay, CNTs to assure alignment and no aggregation).

8. By studying the interlayer distance (diffraction) and polymer chain mobility (Tg and tanδ), the mechanisms for the mechanical properties are explained by a critical interphase which confines and stiffens the polymer chains and enhances interfacial interaction for stress transfer , and also (my personally) the aligned nanosheets sustaining load.  

9. Superspreading clay nanosheets/CNT composite films show ultrahigh strength and toughness (toughness ~20 times that of natural nacre), and show toughening mechanisms of interphase and nanosheet pull-out.

Strengthening and toughening mechanisms are similar, while the most crucial (and thus the novelty) is how to realize these/bring these to happen.

Here is the link of the paper: https://www.nature.com/articles/s41586-020-2161-8

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