“Some graphene-based devices may function to their full capability in dry places while others may do so in humid places. We suggest all experiments on 2D materials should in future record the relative humidity.”Yiwei Sun, Queen Mary University of London

Graphene can exhibit very different properties in humid conditions, say researchers from Queen Mary University of London in the UK.

The ‘wonder material’, which is made from carbon and was discovered in 2004, has been hailed for many of its extraordinary characteristics, including being stronger than steel and more conductive than copper, as well as being light, flexible and transparent. This study, reported in a paper in Physical Review B, shows that in bi-layer graphene, comprising two sheets of one-atom-thick carbon stacked together, water can seep between the layers in a humid environment.

The properties of graphene significantly depend on how the carbon layers interact with each other, and when water enters in between it can modify that interaction. The researchers found the water forms an atomically thin layer at 22% relative humidity and separates graphene layers at over 50% relative humidity.

This suggests that layered graphene could exhibit very different properties in a humid place such as Manchester, UK, where average relative humidity is over 80% every month of the year, compared with a dry place such as Tucson, Arizona. Here, relative humidity is 13% on afternoons in May but rises to 65% on January mornings, meaning the properties of layered graphene will vary according to the time of year.

Graphene, both layered and single layer, potentially has a huge number of uses but the results of this study could impact how the material can be used in real-life applications.

“The critical points, 22% and 50% relative humidity, are very common conditions in daily life and these points can be easily crossed,” said lead author Yiwei Sun from Queen Mary University of London. “Hence, many of the extraordinary properties of graphene could be modified by water in between graphene layers.

“Some graphene-based devices may function to their full capability in dry places while others may do so in humid places. We suggest all experiments on 2D materials should in future record the relative humidity.”

The researchers suggest humidity is also likely to have an impact on other 2D layered materials such as boron nitride (sheets made of boron and nitrogen) and molybdenum disulphide (sheets made of molybdenum and sulphur).

They carried out this study because it was known that graphite, which is made up of many sheets of graphene stacked together, loses its excellent lubricating ability in low humidity conditions. Examples include aboard aeroplanes at high altitude, which was reported during the Second World War, or in outer space, as reported by NASA in the 1970s. It was believed that the water in between layers of graphite is crucial to its behaviour and now the same effect has been shown to affect layered graphene.

This story is adapted from material from Queen Mary University of London, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.