news & views may indeed explain the large viscous-like dissipation generated during interlayer sliding of multiwalled BNNTs. Beyond mechanistic considerations, the work of Niguès and collaborators should help spur studies aimed at understanding how frictional forces at the atomic scale depend on the presence of electromagnetic fields, external mechanical stresses and environmental conditions (such as temperature, relative humidity and ambient-gas composition). For example, in single-walled nanotubes both the presence of defects and nanotube chirality can significantly affect frictional forces, as experiments with a sliding nanosized tip have determined6,7. Yet whether these factors influence interlayer dissipation in multiwalled nanotubes remains to be studied. Similarly, one wonders whether interlayer frictional behaviour in BNNTs and CNTs differs from the friction between adjacent yet non-concentric nanotubes sliding
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past each other. Moreover, by developing the force-sensing tuning fork of Niguès and colleagues to allow for bidirectional nanomanipulation, it may be possible to excite and exploit multiple mechanical resonances in the nanotubes, and thus obtain higher precision in measurements of both radial and axial components of the forces during telescopic sliding 8. Furthermore, Niguès and co-workers’ approach has the potential to be able to measure frictional forces between flakes or nanoribbons of graphene, boron nitride or transition-metal dichalchogenides — materials with two-dimensional crystalline configurations that have been shown to have exceptional electrical, electro-optical and mechanical properties. Ultimately, understanding the friction mechanisms between atomically flat materials should allow us to fabricate structures with ad hoc frictional properties for applications in ultraminiaturized vibration-control and
vibration–actuation devices. With this in mind, playing a violin with strings of nanotube yarn may one day become a reality.
❐
Robert Szoszkiewicz is in the Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA. Elisa Riedo is in the School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA. e-mail: [email protected] References 1. Vanossi, A., Manini, N., Urbakh, M., Zapperi, S. & Tosatti, E. Rev. Mod. Phys. 85, 529–552 (2013). 2. Urbakh, M., Klafter, J., Gourdon, D. & Israelashivili, J. Nature 430, 525–528 (2004). 3. Niguès, A., Siria, A., Vincent, P., Poncharal, P. & Bocquet, L. Nature Mater. 13, 688–693 (2014). 4. Cumings, J. & Zettl, A. Science 289, 602–604 (2000). 5. Zhang, R. et al. Nature Nanotech. 8, 912–916 (2013). 6. Chui, H.‑C., Dogan, S., Volkmann, M., Klinke, C. & Riedo, E. Nanotechnology 23, 455706 (2012). 7. Lucas, M. et al. Nature Mater. 8, 876–881 (2009). 8. Ploscariu, N. & Szoszkiewicz, R. Appl. Phys. Lett. 103, 263702 (2013).
THE CLEAN AIR ACT Most poets probably harbour a hope that their poems might change the world, but none has taken that wish quite as literally as Simon Armitage, whose ‘In Praise of Air’ is the first ‘catalytic poem’. Displayed on a 10 m by 20 m panel on the side of a university building overlooking a busy road in Sheffield’s city centre, it is not just an ode to the vital joys of clean air but is actively producing that very stuff. The panel is coated with a layer of photocatalytic titanium dioxide nanoparticles that, when irradiated with sunlight (or indeed street lights), convert nitrogen oxides (NOx) adsorbed on their surface to nitrate. The project is a collaboration with Sheffield materials scientist Tony Ryan, and has been funded as part of the city’s Lyric festival of literature. As well as breaking down nitrogen oxides, the catalytic nanoparticles transform toxic volatile organic compounds into fatty acids. They are, of course, barely able to make a dent on the fumes from passing vehicles: each square metre of the display removes about 2 g of NOx a day, about as much as is produced by a single bus. But of course the point is to make a difference in another way: to
create a visible and arresting symbol of the need to tackle air pollution. Armitage’s image of “days when thoughts are fuddled with smog/or civilization crosses the street/with a white handkerchief over its mouth” will be all too familiar to many urban dwellers, perhaps especially in China, where today mobile apps tell users whether or not the PM10 index (the level of airborne particulate matter smaller than ten micrometres across) is low enough for children to play safely outside. That same objective motivates the technology from which this project arose: ‘catalytic clothing’, developed by Ryan with designer and artist Helen Storey, who specializes in art–science collaborations for fashion, design and technology. They have devised a process in which the titania nanoparticles can become attached to ordinary clothing fabric (so far cotton, but they are working on other fibres) during the laundering process, so that subsequently the wearer may combat air pollution simply by walking around. Ryan and Storey say that the effects are not insignificant: 30 people in catalytic clothing walking past a metre-width stretch of
PHILIP BALL pavement every minute could effect a noticeable drop in levels of NOx. The duo are still trying to bring the idea to the market. In Praise of Air is also singing the praises of materials. The technology is nothing particularly new, but Ryan’s work is a reminder that bringing a useful laboratory product to the attention of both investors and consumers is often a matter of engaging the imagination — and that this is where scientists can benefit from interactions with designers and artists. It shows too that serious problems can be tackled playfully and in ways that encourage the public to see that they can participate and not be merely the passive recipients of some cryptic and forbidding technology. ❐
NATURE MATERIALS | VOL 13 | JULY 2014 | www.nature.com/naturematerials
© 2014 Macmillan Publishers Limited. All rights reserved
MATERIAL WITNESS 668
past each other. Moreover, by developing the force-sensing tuning fork of Niguès and colleagues to allow for bidirectional nanomanipulation, it may be possible to excite and exploit multiple mechanical resonances in the nanotubes, and thus obtain higher precision in measurements of both radial and axial components of the forces during telescopic sliding 8. Furthermore, Niguès and co-workers’ approach has the potential to be able to measure frictional forces between flakes or nanoribbons of graphene, boron nitride or transition-metal dichalchogenides — materials with two-dimensional crystalline configurations that have been shown to have exceptional electrical, electro-optical and mechanical properties. Ultimately, understanding the friction mechanisms between atomically flat materials should allow us to fabricate structures with ad hoc frictional properties for applications in ultraminiaturized vibration-control and
vibration–actuation devices. With this in mind, playing a violin with strings of nanotube yarn may one day become a reality.
❐
Robert Szoszkiewicz is in the Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA. Elisa Riedo is in the School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332-0230, USA. e-mail: [email protected] References 1. Vanossi, A., Manini, N., Urbakh, M., Zapperi, S. & Tosatti, E. Rev. Mod. Phys. 85, 529–552 (2013). 2. Urbakh, M., Klafter, J., Gourdon, D. & Israelashivili, J. Nature 430, 525–528 (2004). 3. Niguès, A., Siria, A., Vincent, P., Poncharal, P. & Bocquet, L. Nature Mater. 13, 688–693 (2014). 4. Cumings, J. & Zettl, A. Science 289, 602–604 (2000). 5. Zhang, R. et al. Nature Nanotech. 8, 912–916 (2013). 6. Chui, H.‑C., Dogan, S., Volkmann, M., Klinke, C. & Riedo, E. Nanotechnology 23, 455706 (2012). 7. Lucas, M. et al. Nature Mater. 8, 876–881 (2009). 8. Ploscariu, N. & Szoszkiewicz, R. Appl. Phys. Lett. 103, 263702 (2013).
THE CLEAN AIR ACT Most poets probably harbour a hope that their poems might change the world, but none has taken that wish quite as literally as Simon Armitage, whose ‘In Praise of Air’ is the first ‘catalytic poem’. Displayed on a 10 m by 20 m panel on the side of a university building overlooking a busy road in Sheffield’s city centre, it is not just an ode to the vital joys of clean air but is actively producing that very stuff. The panel is coated with a layer of photocatalytic titanium dioxide nanoparticles that, when irradiated with sunlight (or indeed street lights), convert nitrogen oxides (NOx) adsorbed on their surface to nitrate. The project is a collaboration with Sheffield materials scientist Tony Ryan, and has been funded as part of the city’s Lyric festival of literature. As well as breaking down nitrogen oxides, the catalytic nanoparticles transform toxic volatile organic compounds into fatty acids. They are, of course, barely able to make a dent on the fumes from passing vehicles: each square metre of the display removes about 2 g of NOx a day, about as much as is produced by a single bus. But of course the point is to make a difference in another way: to
create a visible and arresting symbol of the need to tackle air pollution. Armitage’s image of “days when thoughts are fuddled with smog/or civilization crosses the street/with a white handkerchief over its mouth” will be all too familiar to many urban dwellers, perhaps especially in China, where today mobile apps tell users whether or not the PM10 index (the level of airborne particulate matter smaller than ten micrometres across) is low enough for children to play safely outside. That same objective motivates the technology from which this project arose: ‘catalytic clothing’, developed by Ryan with designer and artist Helen Storey, who specializes in art–science collaborations for fashion, design and technology. They have devised a process in which the titania nanoparticles can become attached to ordinary clothing fabric (so far cotton, but they are working on other fibres) during the laundering process, so that subsequently the wearer may combat air pollution simply by walking around. Ryan and Storey say that the effects are not insignificant: 30 people in catalytic clothing walking past a metre-width stretch of
PHILIP BALL pavement every minute could effect a noticeable drop in levels of NOx. The duo are still trying to bring the idea to the market. In Praise of Air is also singing the praises of materials. The technology is nothing particularly new, but Ryan’s work is a reminder that bringing a useful laboratory product to the attention of both investors and consumers is often a matter of engaging the imagination — and that this is where scientists can benefit from interactions with designers and artists. It shows too that serious problems can be tackled playfully and in ways that encourage the public to see that they can participate and not be merely the passive recipients of some cryptic and forbidding technology. ❐
NATURE MATERIALS | VOL 13 | JULY 2014 | www.nature.com/naturematerials
© 2014 Macmillan Publishers Limited. All rights reserved
