Smart materials: the future

Saving tomorrow's world

18 May 2010

In their series on smart materials, Chris Mahony and Kevin Tinkham look forward to new technologies and how they could benefit the built environment

Design trends come and go and the popularity of specific building materials fluctuates but, for a variety of reasons, the construction sector is generally quite conservative in its choice of materials and technologies. However, as Bob Dylan once wrote (though, we suspect, not about the construction sector) "The times they are a-changin".

The construction industry is worth £100bn per year to the UK economy but it also creates about 45% of UK CO2 emissions, one third of all landfill and consumes 25% of all raw materials - hence why construction is a major focus for government sustainability targets. For example, the UK government has committed to reduce greenhouse gas emissions over the next 40 years by 80% (compared with 1990 levels) and all new houses built after 2016 should be zero carbon. These targets are ambitious and the technical challenges are demanding, so in this article we look at technologies that may help us to meet these goals.

Aerogel insulation

Aerogels are particularly attractive as insulating materials due to their light weight - typically just 15 times heavier than air - and extremely low thermal conductivity

Aerogels are a diverse class of porous solid materials. They consist of open-celled, solid foams composed of a network of interconnected nanostructures and most have porosity levels of between 90 and 99.8%. Aerogels also exhibit a wide range of extreme properties and hold records including the lowest density solid (0.0011 g cm-3), the highest specific surface area for a monolithic material (3200 m g-1) and the lowest thermal conductivity (0.013 W/mK).

In construction, aerogels are attractive as insulating materials due to their light weight - typically just 15 times heavier than air - and extremely low thermal conductivity. Developed in the US by Aspen Aerogels, the Spacetherm family of insulating products is now supplied in the UK by Proctor Group. By combining a silica aerogel with a robust polyester carrier it is possible to manufacture highly insulating laminate chipboard and plasterboard.

Aerogel insulating products have only recently entered the UK construction sector but are suitable for both new build and refurbishment programmes. As always, care must be taken to follow installation instructions accurately but no specialist training is required. Once in place, Spacetherm products look like any other lining boards and can be decorated in the same way.

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Figure 1: Spacetherm-F is a high-performance laminate comprising Spacetherm insulation blanket bonded to Fermacell. The strength and fire resistance properties of Fermacell and the thermal insulation properties of Spacetherm combine to give a versatile insulated lining board (© Proctor Group)

Figure 2: Spacetherm-PP is a high-performance laminate specifically designed to be used when shot-fired fixing is preferred. It can achieve similar performance to traditional plasterboard laminates, but at a fraction of the thickness, allowing greater flexibility (© Proctor Group)

OLED lighting

When coated onto a film, OLEDs could be used to cover walls creating, in effect, a light-emitting wallpaper that would replace conventional light bulbs entirely

Lighting in buildings accounts for around one sixth of electricity use in the UK. Given the targets for zero carbon buildings and greenhouse gas reductions, this is an area of significant activity and development. Most of us will be aware of the programme to replace traditional incandescent light bulbs with more energy-efficient bulbs and the energy saving potential of LED lighting. Less well known is organic LED (OLED) lighting, but it is this technology that LOMOX is developing for ultra-efficient lighting applications.

The LOMOX OLED lighting, which is currently in development, is said to be 2.5 times more efficient than current energy saving bulbs and has the potential to reduce CO2 emissions globally by almost 7.5m tonnes by 2050. When coated onto a film, OLEDs could be used to cover walls creating, in effect, a light-emitting wallpaper that would replace conventional bulbs entirely.

In addition to being flexible, OLED film will only require a very low operating voltage (3 to 5 volts), meaning it will be capable of being powered by batteries or solar panels. Hence, OLED lighting will be suitable even for remote sites and can be powered by renewable energy technology.

Nanoparticle heat pumps

Scientists have recently described the idea of a heat pump based on nanoparticles that could cool buildings without the need for costly and energy intensive air-conditioning

Though still at the research stage, scientists at the University of Technology in Sydney have recently described the idea of a heat pump based on nanoparticles to cool buildings without the need for energy-intensive air-conditioning. The idea is based on the 'night sky cooling' effect, in which the energy absorbed by a surface during the day is emitted back into the atmosphere at night.

Much of the heat emitted at night is reabsorbed by the atmosphere and subsequently re-emitted back to the earth's surface (and some gases, such as CO2, are very good at absorbing radiation - but you would not want extra amounts of these in the atmosphere). However, some wavelengths - between 7.9 and 13µm - are less likely to be absorbed and the researchers have found that a mixture of silicon carbide and silicon dioxide nanoparticles emits heat radiation within this range. In the heat pump, air or water would flow in channels beneath a plate coated with the nanoparticle mix. The coating would emit radiation and cool the air or water beneath.

Colour change roofs

We have previously discussed the advantages of reflective roof panels to keep internal spaces cooler in hot weather and to reduce stresses on timber joists (see Paint: the final frontier). Of course, this technology only addresses the issue of cooling in hot weather. Now, researchers at the Massachusetts Institute of Technology in the US have developed roof tiles that change colour according to temperature, turning white during hot weather to reflect heat but turning black in cold weather to absorb heat. The MIT team believe that air-conditioning costs in hot weather could be cut by up to 20%.

The concept is quite simple. A common commercial polymer in a water solution is sandwiched between flexible plastic layers, with a dark layer at the back. When the temperature reaches a certain level (determined by the solution composition) the polymer condenses, forming tiny droplets that produce a white reflective surface. Below the predetermined temperature, the polymer stays in solution, revealing the black backing layer that absorbs the sun's heat. Research is currently underway to reduce the cost of the tiles and to establish the long-term durability of the system.

Interestingly, Solar Twin is developing a thermochromic solar collector for its solar water heating systems. Currently, the number of solar panels that can be attached to a hot water cylinder is restricted because of problems with the carrier liquid boiling. Solar Twin's prototype system involves the use of thermochromic paint. In temperatures of up to 70°C, the paint is black and absorbs heat but between 70 and 80°C the paint gradually changes to white, in the process becoming a solar reflector. As the temperature falls, or if someone uses any hot water, the paint becomes black again.

Self-repair coatings

MIT researchers have developed roof tiles that change colour according to temperature, turning white during hot weather to reflect heat but turning black in cold weather to absorb heat

Self-repair is hardly a new idea - organisms have been able to repair damaged bone and tissue for millions of years - and is an attractive concept for building materials. Product lifetimes would be extended, safety improved (as damaged features in hard to access locations would simply self-heal) and costs would be reduced through lower maintenance and refurbishment levels.

Some degree of self-repair can already be achieved in automotive paints but these rely on the resin flowing slowly back to fill light scratches. True self-repair is harder to achieve but construction is a large market and the commercial potential is clear. Perhaps the most likely technology to make a breakthrough will be based upon microcapsules. When the coating is damaged the microcapsules will rupture and the corrosion inhibitors, polymers and pigments they contain will react together to effect a repair. Autonomic Materials in the US appear to be the world leaders in this technology, while a number of university research groups, including those at Bristol and Sheffield in the UK, are investigating alternative methods.

Which of the products discussed will be considered standard in the years to come? Perhaps others will join them. For example, Nanopool are about to launch an ultra-thin silica coating product that is claimed to be food safe, environmentally friendly, easy to clean and antimicrobial; researchers at Tel Aviv University recently described how arrays of self-assembling nanotubes could lead to the next generation of self-cleaning products; and Romag in County Durham already supplies PowerGlaz BIPV, a glass/glass laminate that encapsulates photovoltaic cells for electricity generation and is used as a substitute for ordinary glass.

The number of new materials technologies emerging from innovative companies and research groups continues to grow, offering enormous potential for exploitation in buildings. For most, we cannot yet be sure of in-service performance, nor is it possible to say exactly what their emergence will mean for surveyors. Nevertheless, the sustainability challenge is such that new technologies will definitely be required to help meet future sector targets.  

Chris Mahony is a Director of Church Lukas and Chairman of the RICS Building Pathology Working Group

Kevin Tinkham is a Senior Researcher in the Coated Products Department at Corus Research, Development & Technology

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