C&B Notes

Teflon and Covalent Bonds

Chemists in Australia are pursuing hydrophobic innovation:

When it comes to repelling gunk, car wax and Teflon are among the best materials available.  But they could be better.  A good measure of their lack of stickiness is their “water contact angle” — a way of measuring how effectively the material repels water.  For car wax it is 90° and for Teflon, 95°.  The higher the angle, the more repellent the surface is — and the cleaner it stays.  As anyone with a car or a non-stick frying pan knows, however, the microscopic wax or Teflon layers gradually wear away, and their protective ability is lost.  So finding a way to make the layers bond together more strongly would also keep surfaces cleaner.  Tong Lin, a chemist at Deakin University in Australia, thinks he has found a trick that can both increase the contact angle and improve resilience, using an idea familiar from basic chemistry: the covalent bond.

Normally the layers of Teflon, car wax and substances like them are held together by ionic bonds…  The problem with ionic bonds is that they are easily disrupted by acids and bases — chemicals which, respectively, add electrons to, and take them from, other molecules.  In a covalent bond, by contrast, electron pairs are formed when atoms share electrons, rather than transferring them.  This makes covalent bonds less susceptible to disruption.  Accordingly, Dr Lin and his colleagues tried to build up covalent bonds between the layers of a water-repellent, or hydrophobic, material called cellulose acetate butyrate, which is used to make water-resistant fabrics.  In doing so they not only made it acid- and base-proof, they also improved its gunk-resistance.