User login

Navigation

You are here

keep reading-7

Bin Wang's picture

Layered and scrolled nanocomposites with aligned semi-infinite graphene inclusions at the platelet limit, Liu, et al. Strano, Science, 2016

Novelty/impact/significance:

A stacking and folding method (semi-infinite graphene/polycarbonate (Gr/PC) films, exponential increase in thickness with quadrant fold) to generate aligned Gr/PC composites (~320 layers) that have superior modulus and strength at exceptionally low volume fraction of Gr.

A shear scrolling method to produce Archimedean spiral fibers (transverse rolling a Gr/PC film) that have a telescoping elongation of 110%.

Both represent new methodologies for composites with lowest possible content of reinforcements but significantly improved mechanical, electrical, and optical properties.

Scientific question:

How to fabricate composites containing well-aligned, continuous 2D reinforcements at minimal volume fraction but with exceptional mechanical, electrical, and optical properties?   Method to guarantee the alignment while altering the addition of Grs effectively and efficiently is challenging.

Key of how:

With semi-infinite 2D Grs (aspect ratio large enough), good alignment is a key for mechanical, electrical, optical properties at minimum addition of Gr.

The stacking and folding method (including pressing) produces well-aligned composites whose thickness increases exponentially with each quadrant fold of one multi-layered Gr/PC. Therefore, the property versus volume fraction can be studied within a wide range (0.003 to 2.55%) by varying the thickness through modulating the number of layers, effectively and efficiently, with the alignment guaranteed.

The transverse shear scrolling method using single Gr/PC layer creates composite fiber with similar scaling. The spiral arrangement provides the distinguished telescoping elongation.

 Major points (useful info):

1. For 2D reinforcement, a limit (lower bond of content) for effective reinforcing exists when the aspect ratio reaches infinity (a→∞). Here two fabrication methods makes use of the semi-infinite 2D Gr layer to construct well-aligned planar composites and spiral fiber with wide range of content, demonstrating the a→∞ limit.

2. The stacking and folding method for planar composite: make i layers of semi-infinite Gr/PC films, next fold/cut in a quadrant manner and stack the 4 parts into 1st stacking, then repeat this on 1st stacking j-1 times to for 1x4^j layers, then hot-pressing to obtain composites. The optical transmittance is 98% per layer.

Some descriptions are suggested to add for the stacking and folding method (if I understood correctly): after the quadrant fold/cut, stack the 4 parts to form 1st stacking (ix4^1 1ayers). Then conduct quadrant fold/cut on the 1st stacking and stack to form 2nd stacking (1x4^2 layers).

Repeat this fold/cut and stacking to obtain 1x4^j layers, so that the number of layers (which means the thickness, the volume fraction of Gr) increases exponentially with each quadrant fold and stacking, allowing to alter the varying range of Gr content widely.

3. The transverse shear scrolling method for spiral fiber: a single Gr/PC film folds on one end by a glass capillary, and rolling the film by Si/SiO2 wafer through transverse shear force. The layer spacing is 180/410 nm. The number of layers can be controlled, and the volume fraction ranges from 0.003 to 2.55%.

4. The 4^j composites with very low volume fraction (VG) 0.082 and 0.185% show significantly high tensile storage moduli and loss moduli than PC composite. And 2-5% of 3D random orientation GO (10 times more) is required for comparable stiffness. Nanoreinforcement with smaller aspect ratio/not well-aligned contribute less to reinforcement.

5. The reinforcement of 4^j composites come from the direct load transfer to graphene filler, rather than the inclusions stiffening the matrix by restricting polymer-chain mobility (Tg measurement).

6. The spiral fiber has a measurable increase in stiffness (less significant than the 4^j planar composites), a telescoping compliance mechanism including axial rotation, in-plane translation, interfacial sliding, and a breaking strain 1.10 due to helical telescoping/twisting of the scrolled layers. The scrolling structure requires all the C-C bonds in the Gr to rupture before the complete failure, which absorbs more energy.

7. The methods provide new ways to modify the electrical and optical properties of the matrix with lowest possible amounts of inclusion. The 4^j composites and the scroll fibers show discrete current steps/anisotropic conductivity, allowing for making complex circuits.

The methods are straightforward, efficient and effective compared with ones to achieve good dispersion at scale, to modulate the properties of composites with miniscule additions of nanofillers. The structure of the spiral fiber provides more sites to modulate the mechanical and other interesting functional properties.

 

A good paper organizes its content in such a way that not a single sentence can be removed, nor one needed to add. No more, no less. And reading again (and again) promotes a real understanding of the work and further a correlation to our own.

Here is the link of the full text: https://science.sciencemag.org/content/353/6297/364

Subscribe to Comments for "keep reading-7"

More comments

Syndicate

Subscribe to Syndicate