Graffiti proofing, or more scientifically, making surfaces with a high degree of anti soiling capability has become a subject of considerable attention at TWI recently.
'The clear objective' says project leader Alan Taylor, 'Is to develop a coating that is both abrasion resistant and has a very low surface energy. So effectively we have entered the realm of designing molecules that will undertake specific roles that we require.'
The way Taylor has tackled this is to devise a three component system. Two are very much structurally based on silicates, the third component has a silica aspect to it. It is heavily loaded with fluorine which lowers the surface energy of the coating creating a hydrophobic, or water hating, material with a contact angle well above 90 degrees.
Each individual fluorine atom is linked with a carbon atom, in other words each carbon atom may have two or three fluorines tied to it. Those fluorine atoms are extremely highly polarised electronically, they are very stable and repel the oxygen in the water, making it a very difficult material to which to adhere.
'Our aim is to use the chemistry of the fluorine to give us the desired hydrophobicity' explains Taylor, 'and also the chemistry of silicate systems to give us a three dimensional network that is integral to itself but also allows adhesion to the substrates.'
The TWI team now has a suitable coating under development which features good abrasion resistance and a contact angle between115 and 120 degrees.
'We are aiming to improve on that, the technology is still developing' according to Taylor. 'We are still trying to understand the detailed mechanics of how one does that. What we have done with our partner Visteon is produced a coating which has very good anti coking and anti soiling properties when applied to an aluminium heat exchanger.'
TWI now has a patent for the coating in place in which two of TWI's specialists are named inventors.
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