Graphene thermal conductivity - introduction and latest news - Page 16

Last month we launched a new feature - Experts Roundup. In this feature we ask graphene professionals to answer a short graphene related question. Last month's question was "will CVD ever be a viable commercial way to produce graphene?" and we got great response to that. Hopefully this month feature will be just as good.

In the growing field of graphene-enhanced composites, especially plastics, how does graphene oxide fit in? Does it have any significant advantages over graphene?

Ian Fuller, VP business development & engineering, Angstron Materials : I would classify graphene oxide as a functionalized graphene nanomaterial. Functionalization, in general, allows for tailored nanomaterials for applications such as polymer nanocomposites. The oxygen-based groups on the surface of graphene oxide often promote coupling between the polymer and the nanomaterial leading to enhanced properties such as strength and quality of dispersion (however, electrical and thermal conductivity are often reduced). Similarly, other functional groups can be added to the surface of a graphene platelet to customize it for a range of applications and polymers.

Researchers in Taiwan have shown that graphene could be used as an efficient heat sink between p-n junctions in light-emitting diodes (LEDs). When glued to a polyamide via a titane coupling agent (TCA), reduced graphene improved the thermal conductivity of an interfacial nanocomposite by 53%, compared to a control that contained only the polymer.

In addition to being 53% more thermally conductive than the polyamide polymer alone, the graphene composite also came to a higher equilibrium temperature, signifying better heat transfer. When used to coat the interface, LEDs maintained 95% of their light intensity over 7,000 hours, while the control only maintained about 68%.

Researchers from the University of Groningen and the University of Manchester have directly detected the Peltier effect in graphene that is either one or two atoms thick. The Peltier effect is an example of Thermoelectrics: the field of study that deals with situations in which a temperature difference creates an electric potential, or vice versa. In this effect, a temperature difference appears when a voltage is applied between two electrodes connected to a semiconductor material. The team unambiguously showed that the effect can be switched from heating to cooling by tuning the type and density of the charge carriers inside the material.

The researchers used graphene because of its 2D nature, and graphene is a wonderful candidate for demonstrating a fully tuneable Peltier effect. The electrical contacts to graphene allowed to electrically control the cooling and heating via the Peltier effect, and to detect this cooling and heating, the researchers constructed sensitive nanoscale thermometers that directly measured the temperature of electrons in graphene. This practical approach is said to be the first of its kind for 2D materials, and its sensitivity is a thousand times better than that of its predecessors, down to 0.1 milliKelvin.

Researchers at Chalmers University of Technology have developed an efficient way of cooling electronics by using functionalized graphene nanoflakes. This could come in handy as heat dissipation in electronics and optoelectronics is a major obstacle for the further development of systems in these fields.

According to the researchers, the method is a "golden key" with which to achieve efficient heat transport in electronics and other power devices by using graphene nanoflake-based film. This can open up potential uses of this kind of film in broad areas, and the team states that it is getting closer to pilot-scale production based on this discovery.

Garmor, a graphene technology provider and developer of advanced customer-driven applications, has developed graphene-based composites ideal for high-volume electronic and energy storage applications. By leveraging inexpensive manufacturing methods to produce few-layer graphene oxide (GO) along with innovative composite compression molding processes, Garmor produced compression-moldable GO-composites that can be shaped and stamped into almost any form factor. Garmor is currently establishing strategic business relationships to deploy this technological advancement in applications focused on energy production and storage.

These composites exhibit nearly isotropic electrical conductivity exceeding 1,000 S/cm delivering a unique, omnidirectional conductive substrate. Equally impressive is that these GO-enhanced materials include a polymeric resin that is inherently chemically resistant and allows for increased lifetime even in harsh operating environments.

Oros Apparel is a U.S-based company that manufactures thermal outerwear based on aerogel technology. The company is now developing gloves made from graphene-coated aerogels that keep body warmth inside the gloves and insulate from low outer temperatures. We spoke with them to get a better understanding of their graphene activity.

The company says that the graphene, with its high heat conductivity, is placed between the body and the aerogel, thus helping to trap the body heat inside. This yields better insulation than regular aerogels without graphene. In fact, the company states that it is only making gloves and not jackets or other garments as these would be too warm to wear.

Haydale's Composite Solutions division (HCS) has announced the launch of three graphene enhanced carbon fibre pre-impregnated (prepreg) products, in collaboration with SHD Composite Materials Ltd (Sleaford, Lincolnshire, UK) using epoxy resins from Huntsman Advanced Materials.

The products to be launched include a structural component carbon fibre prepreg, a prototype Out-of-Autoclave curing carbon fibre tooling prepreg capable of fast composite part production in autoclave processing and a higher operating temperature prepreg for enhanced life and very high accuracy tooling.

Note: Xefro was issued an order of liquidation after a legal entanglement and claims of deceiving the public.

Xefro, the UK-based company that is developing a graphene-based heating system, has employed the services of European Circuits Limited (ECL) to design and manufacture the electronics for its innovative heating system. Test systems are currently under trial, and Xefro expects this to be the world’s first commercial heating system using graphene.

Graphene has been selected for the heating element because of its potential for extremely efficient energy transfer, and so the company expects reduced energy costs of up to 70%. The heating system will consist of a Central Heating Controller that will communicate via RF signals to a Hot Water Controller and to the various zones, each zone consisting of a radiator or at least one heating element with AC Power Controller and separate temperature sensors. The user interface for the entire system will be via a mobile app.

Researchers at Rice University have created a thin coating of graphene nanoribbons in epoxy, that has proven effective at melting ice on a helicopter blade. This coating may be an effective real-time de-icing mechanism for aircraft, wind turbines, transmission lines and other surfaces exposed to cold weather. In addition, the coating may also help protect aircraft from lightning strikes and provide an extra layer of electromagnetic shielding.

The scientists performed tests in which they melted centimeter-thick ice from a static helicopter rotor blade in a -4 degree Fahrenheit environment. When a small voltage was applied, the coating delivered electrothermal heat - called Joule heating - to the surface, which melted the ice.

Researchers at Stanford University have developed a revolutionary graphene-enhanced polyethylene film that prevents a lithium-ion battery from overheating, then restarts the battery when it cools. This new technology could prevent fires and melt-downs in a wide range of battery-powered devices.

The researchers in this study recently invented a wearable sensor to monitor human body temperature, made of a plastic material embedded with tiny particles of nickel with nanoscale spikes protruding from their surface. For the battery experiment, they coated the spiky nickel particles with graphene and embedded the particles in a thin film of elastic polyethylene. They then attached the film to one of the battery electrodes so that an electric current could flow through it. The researchers explain that in order to conduct electricity, the spiky particles have to physically touch one another, but during thermal expansion, polyethylene stretches. That causes the particles to spread apart, making the film non-conductive so that electricity can no longer flow through the battery.