Friday, March 18, 2011

Anti-Fog Coating

Fog forms on a surface when water vapor in the air condenses in fine droplets. The fog that forms on glasses is not a continuous film, rather, it consists of tiny droplets of water that coalesce on the surface and reduce light transmission. A good anti-fog coating should prevent the formation of these droplets. Existing anti-fog coatings can't withstand repeated washings so must be re-applied regularly.

Researchers have used polyvinyl alcohol, a hydrophilic compound that allows water to spread uniformly, in the first reported permanent anti-fogging coating.

Four successive layers of molecules, which formed strong bonds with their adjoining layers, were applied to the surface prior to adding the anti-fog compound over this base. The result was a thin, transparent, multilayered coating that does not alter the optical properties of the surface on which it is overlaid. In addition, the chemical bonds that join the different layers ensure the hardness and durability of the entire coating.

Pascale Chevallier, Stéphane Turgeon, Christian Sarra-Bournet, Raphaël Turcotte, Gaétan Laroche. Characterization of Multilayer Anti-Fog Coatings. ACS Applied Materials & Interfaces, 2011; : 110307090243075 DOI: 10.1021/am1010964

Further Reading
Physical and Chemical Changes
Balancing Chemical Equations
Intermolecular Forces
Polymers and Polymerization

Study Questions
  1. Write a word equation to describe the production of fog.
  2. Write a balanced chemical equation to describe the production of fog.
  3. Is the production of fog an example of a physical or a chemical change? Explain your answer.
  4. If vinyl chloride has the formula CH2=CHCl and vinyl acetate has the formula CH3COOCH=CH2, what do you predict the formula for vinyl alcohol to be?
  5. Draw a structure for polyvinyl chloride showing three repeating monomer units.
  6. Draw a structure for polyvinyl acetate showing three repeating monomer units.
  7. Draw a structure for polyvinyl alcohol showing three repeating monomer units.
  8. Using your understanding of intermolecular forces, explain how a coating of polyvinyl alcohol could help water droplets forming on glasses.

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