Common examples of these prefixes are Gigalitres – water reservoirs Megalitres – swimming pools Micrometres – measuring cells under the microscope Nanometres – size of large molecules Emphasize the correct use of prefixes – ML and mL are very different μ m – discuss the use of Greek alphabet in scientific work
Despite the solid appearance, glass is actually in a ‘jammed’ state of matter. • It is somewhere between liquid and solid • It has random un-oriented molecules as opposed to a crystal solid with arranged fixed molecules • It moves very slowly and never quite becomes a proper solid.
The Lotus Leaf Effect Images top to bottom: T. Filewich @ Stock.xchng, Daniel Clarke @ Stock.xchng The leaves of Lotus plants have the unique ability to avoid getting dirty . They are coated with wax crystals around 1 nanometre in diameter and have a special rough surface. Droplets falling onto the leaves form beads and roll off taking dirt with them, meaning the leaves are self-cleaning . Sometimes referred to as “ The Lotus Leaf effect ”
Self Cleaning Glass Images L to R: Francois Schnell @ Flickr, Diamond Shell TM Scientists have mimicked nature at the nanoscale to create glass surfaces that are ‘self-cleaning’ like the Lotus leaf. No more scrubbing of shower screens! Self cleaning glass Normal glass No more Spiderman window cleaner!
Self Cleaning Glass Image: PGG Industries How does it work? Self cleaning glass Normal glass Glass is coated with a layer of nanocrystalline titanium dioxide (TiO 2 ). The titanium dioxide reacts to the ultraviolet (UV) component of sunlight causing a gradual break down and loosening of dirt. This is known as the ‘ photocatalytic ’ stage.
Self Cleaning Glass Image: PGG Industries How does it work? Self cleaning glass Normal glass The reaction also causes the glass surface to become super hydrophilic. This forces water to spread across the surface like a sheet, rather than beading, thereby washing away the loosened debris on the surface of the glass as it falls. This is the ‘ hydrophilic ’ stage.
So Can a Fish Tank Be Self-Cleaning? Self cleaning glass Normal glass Australian company Diamond Shell has made self cleaning aquarium glass called ‘Barracouta Glass’ based on the photocatalytic and hydrophilic process. Image: Danny de Bruyne @ Stock.xchng
Self Cleaning Glass Image: Saint-Gobain Glas How does it work? Self cleaning glass Normal glass Another type of self cleaning glass uses hydrophobicity, not hydrophilicity. This type of glass is given a coating which makes it super hydrophobic, meaning water forms beads and runs of the glass. This type of glass is used indoors, such as in shower screens, where there is no sunlight enable use of the other type of glass.
Image: University of Wisconsin Applying a Monolayer to Glass Besides titanium dioxide in self-cleaning glass, other nano-coatings can be used to change the properties of glass and give it a specific application. Let’s learn about how glass coatings change surface properties.
Glass Nano-Coatings Anti-reflective Glass Self cleaning glass Normal glass Type 1 Glass, is coated with multiple layers of metal oxides such as TiO 2 which have a high refractive index, meaning light passes through them very quickly. The thickness of the layers is related to the wavelength of light, resulting in destructive interference of light reflected off the surfaces, making the glass non-reflective. Type 2 Another method of producing anti-reflective glass is to coat it with a single layer of nanoporous SiO 2 . The refractive index of the porous coating is between that of the glass surface and air, thereby reducing the reflectivity and increasing the transmission of light at the glass surface.
Anti-reflective Glass Self cleaning glass Normal glass OptiView Anti-reflective glass made by Australian company Pilkington.
Other Nano Applications Image: Beijing All Brilliant Technology Co., Ltd Switchable Glass Self cleaning glass Normal glass Switchable glass changes from transparent to opaque. A nano-layer of a rod-like particle suspension is placed between two layers of glass. Under normal conditions, the suspended particles are arranged in random orientations and tend to absorb light, so that the glass panel looks frosted or opaque. But when a voltage is applied, the suspended particles align and let light pass, turning the glass clear.
Other Nano Applications Switchable Glass Self cleaning glass Normal glass Switchable glass was used in the Big Brother house to control the view into the rewards room.
Switchable Glass Self cleaning glass Normal glass Switchable glass has applications in car sun roofs, office buildings, and residential apartments . Skydeck 88 in the Eureka Tower in Melbourne is the only observation deck in the world that can thrill you with 'The Edge' - a glass cube made of switchable glass, which projects 3 metres out from the building and suspended almost 300 metres above the ground, with you in it!
Other Nano Applications Image: John Barrie @ flickr Aerogels Self cleaning glass Normal glass Aerogels have exceptional thermal insulation, are light weight, and translucent. These properties result from the nanoporous structure of the aerogel. The material is 99% air and only 1% solid. In glazing, aerogels have been laminated between two panes of glass for applications where high thermal insulation is required, while still allowing light diffusion.