Most visitors to the recently refurbished St. Pancras Station in London marvel at the station’s grand architecture, but I wonder how many realise that its vast glass roof is actually self-cleaning?

Pilkington Activ™ was developed in the UK, and was the first commercially available self-cleaning glass. It exploits a combination of photocatalysis and hydrophilicity to break down dirt and remove it from the surface, all without the need for cleaning products. The glass is coated with a catalytic titanium dioxide (TiO2) layer which is activated by sunlight to break down organic and inorganic matter. The TiO2 coating is also hydrophilic, so when it rains, the water doesn’t form droplets, but spreads into sheets, allowing the dissolved compounds to run off the surface, and leaves a clean pane of glass behind.

More recently, there have been developments in producing transparent hydrophobic (liquid-repellent) surfaces - work by a group from Harvard, published in Nature Communications in July 2013, reported on the development of a bio-inspired hydrophobic coating which is fully transparent and mechanically durable.

The team from Harvard were inspired by the Nepenthes pitcher plant, a tropical carnivorous plant which has a virtually frictionless surface inside its cupped leaves. It does this by locking in a layer of water within the porous surface, which then behaves as a slick coating. The researchers used this idea to develop SLIPS - Slippery Liquid-Infused Porous Surfaces by infusing a nano/microstructured porous material with a lubricating fluid.

The authors realised that rather than merely coating materials with SLIPS, they could apply the same concept directly to the material to make them slippery. To produce transparent hydrophobic glass, they coated a honeycomb glass network with the same lubricant used in SLIPS. The honeycomb structure confers excellent mechanical stability to the material, and by adjusting the width of the honeycomb ‘cells’, it’s possible to tune its reflectivity to various wavelengths of light.

This coated glass repelled water, octane, wine, olive oil and ketchup, and it demonstrated a reduced adhesion of ice to glass by 99%, all while conferring unmatched mechanical robustness. This concept has many potential applications, from frost-free materials in refrigeration to durable contact lenses and solar panels.

All in all, the future for glass looks transparent, clean and slippery.