glass module
TRANSCRIPT
Glass
Module Outcomes• What is glass?• Definitions of hydrophilic,
hydrophobic, wetting, beading • The ‘Lotus Leaf’ effect• How does self cleaning glass work?• Applications of nanotechnology.
What If?…you could have a fish tank which is
self cleaning?
Image: Danny de Bruyne @ Stock.xchng
What If?…you could see what was in the fridge
without opening it?
Image: Courtesy of Nanotechnology Victoria Pty Ltd
The Bizarre Properties of Glass Is it a solid or a liquid?
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.
Activity 1Glass Basics
• List 5 properties of glass• How is it produced?• What makes it such a useful material?
Experiment 1 Magic Sand
What do hydrophobic and hydrophilic mean?
Image: Courtesy Bridge8/Flinders University
Hydrophilic = Water LovingWhen water hits a hydrophilic surface, it flattens and spreads out to form a thin sheet.
Hydrophilic surface=wetting
Water spreads
Hydrophobic = Water Hating
Image: Viktors Kozers @ Stock.xchng
When water hits a hydrophobic surface, it beads.
Hydrophobic surface=beading
Water beads
Wetting & Beading
Contact angles below 90 indicate good wetting, while contact angles above 90 indicate poor wetting (beading).
Poor wetting (beading)Contact angle > 90°
Good wetting Contact angle < 90°
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 ShellTM
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 (TiO2). 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 looseneddebris 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.
Experiment 2Glass Nano Coatings
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-CoatingsAnti-reflective Glass
Self cleaning glass Normal glass
Type 1Glass, is coated with multiple layers of metal oxides such as TiO2 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 2Another method of producing anti-reflective glass is to coat it with a single layer of nanoporous SiO2. 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, thesuspended particles are arranged in random orientations and tend to absorb light, so that the glasspanel looks frosted or opaque. But when a voltage is applied, the suspended particles align and let light pass, turning the glass clear.
Other Nano ApplicationsSwitchable 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.
Activity 2Research other nano applications in glass.
• Conductive glass• Solar heat control• Any others?
The Future•Nanotechnology provides new materials that could potentially have profound affects on building design.•For instance, glass can be used more liberally if it is optically tuned to block heat and UV. •It would be possible to construct a building with many more, larger windows than is currently viable, since heat can be kept out and UV photo-damage prevented.
Image: University of Technology, Sydney
Revision1. List some properties of glass2. Define hydrophilic, hydrophobic,
wetting and beading3. Describe the ‘Lotus Leaf’ effect4. How does self cleaning glass work?5. List 5 examples of glass with
enhanced properties.
