The complementary properties of graphene and glass mean that they go together hand in hand excellently. The development of such fusions continues to be especially beneficial to the automotive industry.
Graphene is a wonder material that is often promoted for its novel physical properties. This material, which consists of a single layer of carbon atoms in a two-dimensional hexagonal lattice arrangement, has mechanical strength, electric and thermal conductivity, and flexibility, thus making it an important component in the development of electronics. But this remarkable material has another, often less touted property, that, when coupled with these aspects, makes it useful for the development of glass and window films — it is optically transparent.
The strength and optical transparency of graphene mean strong commercial motivation in creating and improving a graphene/ glass fusion. This is of particular interest in the automotive industry.
STEK Automotive is just one of many developers in the field that is pursuing just such a development. As part of this, the US-based company has just announced the launch of a premium nano-ceramic window film, NEX. The nano-ceramic window-film contains graphene alongside tungsten and antimony tin oxide to provide drivers with crystal clarity as well as UV and glare reduction. These latter two substances are effective infrared absorbers meaning the film prevents heat from reaching vehicle interiors.
As NEX provides these benefits, it also allows electromagnetic signals to pass through it without hindrance, thus resulting in no disruption to electronic and communication devices within the vehicle.
Whilst an important step for graphene-based glass films, NEX isn't the first time that researchers have attempted to unite the complementary properties of these.
Ever since graphene was first isolated from graphite in 2004, it has attracted great research interest. This has included various attempts to integrate it with glass creating the combination of graphene and glass that endows noticeable electrical/thermal conductivity and surface hydrophobicity without sacrificing the transparency of conventional glass.
Part of the reason integrating glass and graphene became such an area of focus was that it was found that graphene could be used as a surrounding material that is transparent and tough. This is because it is only one-atom thick and each layer of graphene only absorbs 2% of the light that falls upon it. This is because the electromagnetic fields of graphene are strongly confined to its monolayer³ but electrons are free to move across its surface.
Free electrons can only absorb a small amount of energy. And because photons of particular wavelengths come within packages of fixed amounts — or quanta — of energy, the free electrons can only absorb a limited set of photons.
This means that the optical transparency of graphene and its electrical conductivity means that when it is coupled with glass, it isn't just useful for windows and windscreens. Graphene can also be useful for the creation of highly flexible conductive wires, multifunctional fibers, and highly-precise sensors³.
The strength of graphene arises from the fact that the carbon atoms are arranged in a regular arrangement in a lattice joined by covalent bonds. But, there is another benefit that graphene grants glass related to its durability that goes beyond tensile strength.
Graphene and Glass
We're all familiar with the risk of breakage that comes associated with glass. There is no doubt that the addition of graphene to glass improves its tensile strength and makes it more durable.
What is less familiar though, is the fact that glass can also be vulnerable to corrosion. Over time, at high humidity and pH levels, many types of glass can begin to corrode. Corroded glass loses its transparency and its strength is reduced.
In 2016, researchers at the Center for Multidimensional Carbon Materials (CMCM) within the Institute for Basic Science (IBS), pioneered a graphene coating that protects glass from corrosion⁴.
Creating graphene integrated glass has usually involved casting graphene nanoplatelets on glass or transfer-coating of graphene films grown on metals, but another inventive method has been to directly grow graphene on glass². This method, used by the IBS team, eliminates contamination and potential damage that can be caused during integration resulting in a more high-quality glass/graphene mash-up.
Corrosion can begin because of the adsorption of water on the glass surface. Hydrogen ions from water then diffuse into the glass and exchange with the sodium ions present on the glass surface. The pH of the water near the glass surface increases, allowing the silicate structure to dissolve. Thus, the hydrophobic qualities of graphene can help mitigate this. As a result and because of its chemical inertness, graphene is an excellent chemical barrier when used as a thin-coating material. These qualities mean that graphene could also be used to protect other areas of vehicles, such as paintwork, bodywork, and wheel trims.
¹ NEX: Premium Nano-ceramic Window Film, STEK Automotive, , [https://www.stekautomotive.com/windowfilm/nex]
²Chen. X. D., Chen. Z., Sun. J., Zhang. Y. F., , 'Graphene Glass: Direct Growth of Graphene on Traditional Glasses,' ACTA Physico-Chima Sinica, [DOI: 10.3866/PKU.WHXB201511133]
³ Sun. L., Jiang. C., , 'Ultra-thin Glass Film Coated with Graphene: A New Material for Spontaneous Emission Enhancement of Quantum Emitter,' Nano-Micro Letters, [https://doi.org/10.1007/s40820-015-0037-5]
⁴ Wang. B., Cunning. B. V., Park. S-Y., Huang. M., et al, , 'Graphene Coatings as Barrier Layers to Prevent the Water-Induced Corrosion of Silicate Glass,' ACS Nano, DOI: 10.1021/acsnano.6b04363