Thin films or coatings are thin materials layers ranging from fractions of a nanometer to several micrometers in thickness. They are usually applied to a surface to decorate, preserve, protect, seal, or smooth the underlying substrate or to alter the nanotechnology is being done on thin films and coatings and a myriad of applications is conceivable.
Thermal isolation of building facades are under the constant corrosive issue in construction engineering. Although costs of investment (or disposal as in the case of asbestos) can be high, the savings in energy can be equally so. Besides financial benefits, motives concerning the environmental footprint following an investment may be clear as well. Nanoporous materials like aerogels and certain polymer foams provide excellent capabilities in this area.
The surfaces of building facades are under the constant corrosive influence of weathering, fumes or micro-organisms. Nanotechnology offers interesting ways to counteract these unwanted effects with the use of special coating constituents. More benefits can result from the application of TiO2 nanoparticles in coating material to coat entire roadways. The TiO2 coating captures and breaks down organic and inorganic air pollutants via a photo catalytic process. In one test the asphalt surface of a thousand foot stretch of road outside Milan, Italy with an average traffic flow of a thousand vehicles an hour showed a reduction of about 60 percent in nitrogen oxides at street level.
NANOTECHNOLOGY AND GLASS
A lot of research is being carried out on the application of nanotechnology to glass. Titanium dioxide (TiO2) is used in nanoparticles form to coat glazing. It has sterilizing and anti-fouling properties. The particles catalyze powerful reactions which breakdown organic pollutants, volatile organic compounds and bacterial membranes. In addition, TiO2 is hydrophilic and this attraction to water form sheets out of rain drops which then wash off the dirt particles broken down in the previous process. Glass incorporating this self cleaning technology is available on the market today. Fireprotective glass is another application of nanotechnology. This is achieved by using a clear intumescent layer sandwiched between glass panels (an interlayer) formed of fumed silica (SiO2) nanoparticles which turns into a rigid and opaque fire shield when heated.
Most of glass in construction is one the exterior of buildings. The control of light and heat entering through building glazing is a major sustainability issue. Research into nanotechnological solutions to this centers around four different strategies to block light and heat coming in through windows. Firstly, thin film coating are being developed which are spectrally sensitive surface applications for window glass. These have the potential to filter out unwanted infrared frequencies of light (which heat up a room) and reduce the heat gain in buildings; however, these are effectively a passive solution.
As an active solution, thermo chromic technologies are being studied which react to temperature and provide thermal insulation to give protection from heating whilst maintaining adequate lighting. A third strategy, that produces a similar outcome by a different process, involves photo chromic technologies which are being studied to react to changes in light intensity by increasing absorption. And finally, electro chromic coating are being developed that react to changes in applied voltage by using a tungsten oxide layer; thereby becoming more opaque at the touch of a button.
Another example of “nano-enhanced” glass comes with the use of the so-called lotus effect. This effect is named after the observed self-cleaning property of the leaves of the lotus plant. Their microscopic structure and surface chemistry mean that the leaves never get wet. Rather, water droplets roll off a leaf’s surface, taking mud, tiny insects, and contaminants with them. Artificially this can usually be achieved by treatment of the surface with SiO2 or silver nanoparticles held in colloidal solutions typically of water or alcohol. The particles adhere to the substrates molecules and self-organise into a thin layer. After evaporation of the carrying solution, a very long lasting hydrophobic surface is created. Contaminants are simply washed off by rain or when rinsed with water.
