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Wetting

Contact with what?

Nature Materials volume 12, pages 872–873 (2013)Cite this article

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Pristine graphitic surfaces seem to be more hydrophilic than previously assumed because of the unexpected influence of the quick adsorption of hydrocarbons from air.

One of the simplest and most intuitively useful parameters for characterizing a surface is the angle of contact that it forms with a deposited droplet of water. For instance, a small contact angle such as 30° indicates that water spreads fairly well on the surface, that is, that the surface is reasonably hydrophilic. Even a rough estimation of the contact angle can be richly informative. For example, consider how water wets the surface of a car as it goes through a washing-and-waxing cycle. Water droplets will spread out over the initially dirty (and hydrophilic) car, but as soon as the surface is waxed, the hydrophobic coat causes the water droplets to bead up and roll off. One could, in fact, reasonably track the steps involved in cleaning a car simply by monitoring how the contact angle that water makes with the hood of the car changes over the course of the cleaning process. This is similar to the approach — reported in Nature Materials — that Lei Li, Haitao Liu and colleagues used to study the surface of graphene1. The researchers began with a clean surface and watched how the water contact-angle evolved as molecular contaminants from the environment adsorbed on it. Surprisingly, they found that the pristine graphene surface seemed to be more hydrophilic than had previously been assumed, whereas the contaminated surface matched the hydrophobic character that had been ascribed to clean graphene. This first effort to experimentally clarify the intrinsic versus apparent wettability of graphene is thus especially illuminating.

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Figure 1: Effect of the exposure of copper-supported single-layer graphene to airborne hydrocarbons1.

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Authors and Affiliations

  1. Ke Xu is at the Department of Chemistry, University of California, Berkeley, California 94720, USA,

    Ke Xu

  2. James R. Heath is at the Division of Chemistry and Chemical Engineering, California Institute of Technology, 1200 E California Boulevard, Pasadena, California 91125, USA,

    James R. Heath

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  1. Ke Xu
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  2. James R. Heath
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Correspondence to Ke Xu or James R. Heath.

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Xu, K., Heath, J. Contact with what?. Nature Mater 12, 872–873 (2013). https://doi.org/10.1038/nmat3763

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