Giant flakes make graphene oxide gel

Oct 20, 2011
A single flake of graphene oxide roughly 40 microns wide, seen under an electron microscope, sits atop a copper support. Such "giant" flakes form into a gel-like liquid crystal in solution. Credit: Rice University/University of Colorado at Boulder

(PhysOrg.com) -- Giant flakes of graphene oxide in water aggregate like a stack of pancakes, but infinitely thinner, and in the process gain characteristics that materials scientists may find delicious.

A new paper by scientists at Rice University and the University of Colorado details how slices of graphene, the single-atom form of carbon, in a solution arrange themselves to form a nematic liquid crystal in which are free-floating but aligned.

That much was already known. The new twist is that if the flakes – in this case, graphene oxide – are big enough and concentrated enough, they retain their alignment as they form a gel. That gel is a handy precursor for manufacturing metamaterials or fibers with unique mechanical and electronic properties.

The team reported its discovery online this week in the Royal Society of Chemistry journal Soft Matter. Rice authors include Matteo Pasquali, a professor of chemical and biomolecular engineering and of chemistry; James Tour, the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science; postdoctoral research associate Dmitry Kosynkin; and graduate students Budhadipta Dan and Natnael Behabtu. Ivan Smalyukh, an assistant professor of physics at the University of Colorado at Boulder, led research for his group, in which Dan served as a visiting scientist.

"Graphene materials and fluid phases are a great research area," Pasquali said. "From the fundamental point of view, fluid phases comprising flakes are relatively unexplored, and certainly so when the flakes have important electronic properties.

"From the application standpoint, graphene and graphene oxide can be important building blocks in such areas as flexible electronics and conductive and high-strength materials, and can serve as templates for ordering plasmonic structures," he said.

By "giant," the researchers referred to irregular flakes of graphene oxide up to 10,000 times as wide as they are high. (That's still impossibly small: on average, roughly 12 microns wide and less than a nanometer high.) Previous studies showed smaller bits of pristine graphene suspended in acid would form a liquid crystal and that graphene oxide would do likewise in other solutions, including water.

Graphene oxide flakes in a solution align themselves with a director, a dimensionless vector that represents the preferred orientation of particles in a liquid crystal. Credit: Rice University/University of Colorado at Boulder

This time the team discovered that if the flakes are big enough and concentrated enough, the solution becomes semisolid. When they constrained the gel to a thin pipette and evaporated some of the water, the graphene oxide flakes got closer to each other and stacked up spontaneously, although imperfectly.

"The exciting part for me is the spontaneous ordering of graphene oxide into a , which nobody had observed before," said Behabtu, a member of Pasquali's lab. "It's still a liquid, but it's ordered. That's useful to make fibers, but it could also induce order on other particles like nanorods."

He said it would be a simple matter to heat the concentrated gel and extrude it into something like carbon fiber, with enhanced properties provided by "mix-ins."

Testing the possibilities, the researchers mixed gold microtriangles and glass microrods into the solution, and found both were effectively forced to line up with the pancaking flakes. Their inclusion also helped the team get visual confirmation of the flakes' orientation.

The process offers the possibility of the large-scale ordering and alignment of such plasmonic particles as gold, silver and palladium nanorods, important components in optoelectronic devices and metamaterials, they reported.

Behabtu added that heating the gel "crosslinks the flakes, and that's good for mechanical strength. You can even heat enough to reduce it, stripping out the oxygen and turning it back into graphite."

Explore further: Mirror-image forms of corannulene molecules could lead to exciting new possibilities in nanotechnology

More information: pubs.rsc.org/en/content/articl… g/2011/sm/c1sm06418e

Related Stories

Liquid method: pure graphene production

May 30, 2010

In a development that could lead to novel carbon composites and touch-screen displays, researchers from Rice University and the Technion-Israel Institute of Technology today unveiled a new method for producing ...

Graphite + water = the future of energy storage

Jul 15, 2011

A combination of two ordinary materials – graphite and water – could produce energy storage systems that perform on par with lithium ion batteries, but recharge in a matter of seconds and have an ...

Recommended for you

Tiny graphene drum could form future quantum memory

Aug 28, 2014

Scientists from TU Delft's Kavli Institute of Nanoscience have demonstrated that they can detect extremely small changes in position and forces on very small drums of graphene. Graphene drums have great potential ...

Graphene reinvents the future

Aug 27, 2014

For many scientists, the discovery of one-atom-thick sheets of graphene is hugely significant, something with the potential to affect just about every aspect of human activity and endeavour.

User comments : 3

Adjust slider to filter visible comments by rank

Display comments: newest first

Callippo
not rated yet Oct 20, 2011
Unfortunately, the reduction of graphite oxide never lead to graphene monolayers of quality suitable for fabrication of thin layer electronics. We could make some supercapacitors or maybe touch screen electrodes with using it, but not transistors.
fmfbrestel
4 / 5 (1) Oct 20, 2011
Callippo -- Not directly but could see a lot of other researchers playing around with liquid crystal graphene trying to see what they can do with it. It is a very interesting material to have.

I also think its actually pretty cool that it can be used to create custom graphite molds. I agree with the author that metamaterial guys are going to love this stuff.
antialias_physorg
4 / 5 (1) Oct 21, 2011
The value here is more in the extremely high order over a large area/volume. This stuff can then be used as seeds/templates for structuring other materials.