Effective Antireflection Coatings of Transparent Polymeric Materials by Gas-Phase Surface Fluorination

There is a dramatic need in solar energy collection systems for lightweight, inexpensive polymeric materials that exhibit improved performance and durability. One approach to altering the properties of polymeric materials, surface fluorination, is appealing because of its potential for low cost. The literature indicates that such properties as permeability, wettability, bondability, thermalstability, weatherability, and optical transmittance can be improved by treating the surface with gaseous fluorine. A gas phase fluorination reactor system (GPFRS) was designed, built, and used. The initial emphasis was on improving optical transmittance by having an effective antireflection coating form on the surface of a wide variety of commercially available transparent polymeric films.These included such materials as polypropylene, acrylic, polyacrylonitrile, highly cross-linked polyethylene, polyester, polycarbonate and polymethylpentene. Two techniques were used to quantify the effect of effect of exposing the surface of the polymers to gaseous fluorine. Transparent films were characterized before and after fluorine exposure by specular transmittance measurements. Surfaceanalysis of selected treated and untreated samples was accomplished by x-ray photoelectron spectroscopy and depth profiling. Surface analysis confirmed the deposit of fluorine at the surface and into the bulk of all specimens examined after treatment in the GPFRS. Optical measurements revealed sub?stantial improvement in specular transmittance following surface fluorination of almost allmaterials considered. Increases in solar weighted specular transmittance as high as 4.696 were measured.