Material of the Month
Why can’t I see out my car’s windshield?
Summer is here. It gets hot. Whether your car is new or older, it seems that suddenly, the windshield gets so cloudy that you can’t see out of it when the sun is at a particular, usually low angle. So what is that stuff, and how does it get there?
Years ago, analyses showed that the film that builds up on the inside of the car’s windshield was composed of plasticizers and other organic components that evolved from the plastic and vinyl surfaces inside the vehicle. Many of those compounds were later placed on lists of possible carcinogens, and the auto industry started programs to eliminate those nasty materials.
But the windshield still develops a film. In this case, the vehicle was five months old and had leather interior – minimizing the amount of vinyl and other plastics. So the windshield was scraped with a razor blade to remove the filmy buildup for analysis. The technique of choice was Fourier Transform Infrared Spectroscopy (FTIR) of the bulk material, as well as the residue extracted with pentane (which when dried, resulted in the droplet image).
Even after drying, the material contained quite a bit of water. The acquired FTIR spectrum is shown at the bottom, with the computer library-matched component spectra shown above it. The material appears as a mixture of water, sulfonate surfactants, and severely oxidized organic compounds and organic acid “salts,” or carboxylate “soaps.”
Our conclusions? Cleaner residues from the initial vehicle detailing left some soapy residue on the glass. As we all know, incomplete rinsing seems to attract dirt. And when the vehicle cools after baking all day in the hot sun, the cooler glass acts as a ‘getter,’ attracting the normal environmental contaminant molecules to its cooler surface where they eventually reach a thickness that can be seen as a haze when lighted at an appropriate angle.