Glass Module Outcomes What is glass Definitions of

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 1 Glass 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 Bridge 8/Flinders University

Hydrophilic = Water Loving When water hits a hydrophilic surface, it flattens and spreads out to form a thin sheet. Water spreads Hydrophilic surface =wetting

Hydrophobic = Water Hating When water hits a hydrophobic surface, it beads. Water beads Hydrophobic surface =beading Image: Viktors Kozers @ Stock. xchng

Wetting & Beading Poor wetting (beading) Contact angle > 90° Good wetting Contact angle < 90° Contact angles below 90 indicate good wetting, while contact angles above 90 indicate poor wetting (beading).

The Lotus Leaf Effect 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 selfcleaning. Sometimes referred to as “The Lotus Leaf effect” Images top to bottom: T. Filewich @ Stock. xchng, Daniel Clarke @ Stock. xchng

Self Cleaning Glass Scientists have mimicked nature at the nanoscale to create glass surfaces that are ‘self-cleaning’ like the Lotus leaf. Self cleaning glass Normal glass No more scrubbing of shower screens! Images L to R: Francois Schnell @ Flickr, Diamond Shell. TM No more Spiderman window cleaner!

Self Cleaning Glass How does it work? Glass is coated with a layer of nanocrystalline titanium dioxide (Ti. O 2). The titanium dioxide reacts to the ultraviolet (UV) component of sunlight causing a gradual Self cleaning glass Normal glass break down and loosening of dirt. This is known as the ‘photocatalytic’ stage. Image: PGG Industries

Self Cleaning Glass How does it work? 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 Self cleaning glass Normal glass away the loosened debris on the surface of the glass as it falls. This is the ‘hydrophilic’ stage. Watch Video-http: //kitson. co. uk/Whats. New. html Image: PGG Industries

So Can a Fish Tank Be Self-Cleaning? Australian company Diamond Shell has made self cleaning aquarium glass called ‘Barracouta Glass’ based on the photocatalytic and hydrophilic process. Self cleaning glass Normal glass Watch animation - http: //www. nanovic. com. au/flash/barracouta. swf Image: Danny de Bruyne @ Stock. xchng

Self Cleaning Glass How does it work? Another type of self cleaning glass uses hydrophobicity, not hydrophilicity. Self cleaning glass Normal glass 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 indoors, such as in shower screen, where there is no sunlight enable use of the other type of glass. Watch video-http: //www. kitson. co. uk/Whats. New. html Image: Saint-Gobain Glas

Experiment 2 Applying a Monolayer to Glass Nano Coatings 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. Lets learn about how glass coatings changes surface properties. Image: University of Wisconsin

Glass Nano-Coatings Anti-reflective Glass Type 1 Glass, is coated with multiple layers of metal oxides such as Ti. O 2 which have a high refractive index, meaning light passes through them very quickly. Self cleaning glass Normal glass 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 Si. O 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 Opti. View Anti-reflective glass made by Australian company Pilkington. Self cleaning glass Normal glass

Other Nano Applications Switchable Glass Switchable glass changes from transparent to opaque. An nano-layer of a rod-like particle suspension is placed between two layers of glass. Under normal conditions, the Self cleaning glass Normal glass 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. Image: Beijing All Brilliant Technology Co. , Ltd

Other Nano Applications Switchable Glass Switchable glass was used in the Big Brother house to control the view into the rewards room. Self cleaning glass Normal glass

Switchable Glass Switchable glass has applications in car sun roofs, office buildings, and residential apartments. Self cleaning glass Normal glass 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 Aerogels have exceptional thermal insulation, are light weight, and translucent. Self cleaning glass Normal glass 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. Image: John Barrie @ flickr

Activity 2 Research 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 photodamaged prevented. Image: University of Technology, Sydney

Revision 1. List some properties of glass 2. Define hydrophilic, hydrophobic, wetting and beading 3. Describe the ‘Lotus Leaf’ effect 4. How does self cleaning glass work? 5. List 5 examples of glass with enhanced properties.