Graphene: The latest fashionable material
By Adolfo Benedito

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Graphene is that magic word everyone is talking about. This popular, highly praised material is expected to give rise to revolutionary and astonishing applications. Its commercial implementation, for those working with the material, is going to take place in record time in comparison with any other material belonging to the so-called historical materials. Without a doubt, it is something revolutionary. But, as always, we must not forget that behind the impressive facade we can find doubts, questions and gray areas. As proven by history: pie-in-the-sky dreams never come true.

INDUSTRY PULSE

Which property of graphene holds the most promise?
  • 1. Self-cooling
  • 2. Electric/thermal conductivity
  • 3. Resistance greater than steel
  • 4. High elasticity and hardness
  • 5. Other

Graphene is not something new that has appeared out of nowhere. For several years — more specifically 50 years — its existence has been theorized. In fact, P.R. Wallace in 1949 described the electronic stripes structure of graphene. Since then, the term "graphite monolayer" has been used frequently, long before the word graphene itself.

But why? What is graphene? It is derived from carbon hexagonal cycles at 120-degree angles motivated by its hybridization sp2. These cycles form enormous carbon hexagonal layers of an atom wide. This structure is — given the extraordinary capacity of electronic movement — unique and different from anything seen until now. The velocity of the electrons is only 400 times inferior to light, which provides relativist behaviors — even at very low temperatures — and noteworthy quantum effects.

It is, furthermore, the fundamental "brick" of other extraordinary materials: graphite, because graphite is the successive stacking of graphene layers; carbon nanotubes, obtained by winding the layers in cylindrical structures; fullerene, obtained by winding the layers in the form of spheres.
Graphene is derived from carbon hexagonal cycles at 120-degree angles motivated by its hybridization sp2. These cycles form enormous carbon hexagonal layers of an atom wide.

As a result we have a material with properties that on paper are absolutely overwhelming:
  • Self-cooling
  • Impressive electric and thermal conductivities (electric: 0.96106 [Ωm]-1 similar to copper and superior to silicon, and thermal of 5000 Wm-1K-1 for which it is second to none
  • Resistance is 200 times greater than steel
  • Resists ionizing radiations
  • Very light, similar to carbon fiber but more flexible
  • lesser Joule effect (it heats up less when conducting electricity)
  • Generates electricity when reached by light (photodetector, energy storage, sensors)
  • Transparent to light
  • Total gas barrier
  • High elasticity and hardness (it is almost impossible to scratch or penetrate the structure). In fact it is said that the tip of a pencil supporting the weight of a vehicle wouldn't be able to penetrate a graphene layer.
It's marvelous, without a doubt. But until recently there was a "small" problem. There was no graphene. There were only theories, a toy for theoretical physics that was still untouchable. Even the scientific community wondered if this material would be stable under ordinary conditions.

Until — in the first years of the past decade — Andre Geim and Konstantin Novoselov achieved it in the simplest way possible: peeling the graphite layers off the lead of a pencil until obtaining individual layers. One by one. They won the Nobel Prize for Physics in 2010 for their so-called "adhesive tape technique."

Since then, the most diverse techniques for obtaining graphene on an industrial level are being developed. Chemical and thermal methods that involve the exfoliation of graphite, the breakage and opening of carbon nanotubes, carbon vapor deposition (CVD) methods and other various techniques. As a result, at present it is possible to obtain industrial graphene in powder form or as individual layers, which can reach 40 to 50 inches diagonal (MIT considered building a graphene layer of 1 km2). The prices, obviously unaffordable a couple of years ago, continue to decline unstoppably.

In terms of applications, the possibilities seem confusing. Making use of the impressive electronic properties, graphene can be expected to make a triumphal entry into the world of consumer microelectronics. 1,000 GHz-plus processors, light and flexible batteries, OLED ultra-slim, transparent and completely flexible flat screens, are some of the applications we only have to wait a few years for. In fact, large multinationals like Samsung have developed procedures to manufacture functional screens of 50 inches on an industrial level. Flexible devices are expected in a couple of years.

In the world of polymers, the use of graphene provides important technological opportunities. The long list of prodigious properties includes precisely some of the most requested properties by the latest polymeric materials. Transparency, hardness, abrasion resistance, antimicrobial properties, electrical and thermal conductivity, barrier properties, photodetectors, sensors and mechanical properties are some of the possibilities presented to us.

Currently we are beginning to see two different ways of incorporating graphene into a polymeric material: in mass from the powdered graphene (composite material); and surface coating with graphene layers. Both ways cast certain doubts: Will the impressive properties of graphene transfer to a polymer composite material? Will a graphene coating have enough adhesion and elasticity to lose shape in a thermoforming process?

The future looks very promising, but sometimes promises come to naught. For now graphene is booming. Some even call it a divine material. We have at least made a start.

Adolfo Benedito has PhD in chemistry from the University of Valencia, focusing on ABS copolymer degradation and recycling capabilities. Since 2001, he has been working at AIMPLAS as head of the compounding department until 2009, and currently as head of materials research department. He has been the main technical responsible for several EU-research and national projects, as well as author and co-author of several papers and book chapters focused on nanotechnology applied to polymeric materials.