Nanotechnology on Earth and Beyond Series
There are several nanomaterials that have found their way into the construction and composites industries. Titanium dioxide (TiO2) and carbon nanotubes (CNT) are the most prominent ones that have impacted the fore-mentioned sectors, and have the most diverse applications.
Titanium dioxide (titania, TiO2) is a naturally occurring oxide of titanium and widely used as white pigment because of its brightness. TiO2 is a photocatalyst under visible and UV light  and can oxidize oxygen and organic materials. As a result, it has been added to paints, cements, windows, tiles, or other products to provide sterilizing, deodorizing and anti-fouling properties (2). When incorporated into outdoor building materials, TiO2 can substantially reduce concentrations of airborne pollutants especially nitrogen oxides and volatile organic compounds (VOCs) (3). This technology can also be used to make eco-friendly roads; a coating of TiO2 on a 7000-m2 area of road in Milan, Italy gave a 60% reduction in nitrous oxides (4). Additionally, when TiO2 is exposed to UV light, it becomes increasingly hydrophilic (attractive to water), thus it can be used for self-cleaning glasses and anti-fog coatings (5). The “Jubilee Church” in Rome is an excellent example of this and has maintained its original appearance since 2003 thanks to a TiO2 coating that breaks down and decomposes organic compounds, which are eventually washed off when it rains (6).
A Carbon Nanotube (CNT) is a cylindrical arrangement of carbon atoms with diameters ranging from 0.8 to 20 nm, and lengths from 100nm to centimeters thus bridging the gap between the molecular and macroscopic scales (7). They are the most promising of nanomaterials and possess many unique properties. They exhibit extraordinary strength with 5 times the Young’s Modulus (a material’s property that describes its stiffness, and is equal to the ratio of stress applied to the material to the strain) and 8 times (theoretically 100 times) the strength of steel while being only 1/6th of its density (8). In addition they have unique electronic and chemical properties such as high electrical conductivity and chemically inert surface. Though currently the carbon nanotubes are expensive $20 to $1000 per gram depending on quality (9), their manufacturing costs are falling rapidly and already we are seeing tons of applications using CNTs tennis rackets, memory and medical devices to name a few.
The first industrial application of carbon nanotubes was as conductive fillers in plastics. CNT-polymer composites can reach very high conductivities even when loaded with very small amounts of CNTs (10% by weight) (10). This has enabled electrostatic-assisted painting of mirror housings, automobile mirror housings are made of insulating materials like plastic and will need a thin coating of conductive primer in-order to enable electrostatic painting. When these housings are made of CNT-polymer composites, electrostatic coatings can be carried out without any conductive primer coating. In addition they can be used in fuel lines and filters that dissipate electrostatic charge NASA and the Air Force are using these composites for electromagnetic interference (EMI)–shielding of their onboard sensitive electronic equipment such as radar and radios (11), without adding additional weight to their satellites and aircrafts (12).
CNT resins are also used to enhance strength, weight and environmental resistance properties of fiber composites (13)(14) and have recently been used in wind turbine blades (Amroy Europe Oy) and hulls for maritime security boats (CNT coatings also discourage attachment of algae and barnacles) (15). CNTs can also be used to change the viscosity of the plastics and make it flame-retardant (16). An example of where technologies based on these unique properties of carbon nanotubes can be applied, is shown in Figure 1.
Figure 2: Artistic rendition of space transportation using carbon nanotubes (Source NASA).