An Investigation of Microstructural Characteristics of Contact-lens Polymers
National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Division, 1990 - Contact lenses - 8 pages
The free volume and gas permeability in several contact-lens samples have been measured as part of a space commercialization program. Free volume was measured by using positron lifetime spectroscopy, while permeability for 02, N2, and CO2 gases was measured by using mass spectrometry and polarography. Permeability for all gases increases with the mean free-volume cell size in the test samples. As might be expected, the samples with the highest free-volume fraction also exhibit the lowest Rockwell hardness number. An interesting corollary of this study is the finding that the presence of fluorine atoms in the lens chemical structure inhibits the filling up of the free-volume cells. This is expected to allow the lenses to breathe freely while in actual use.
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Abe Eftekhari Abstract The free allow the lenses Characteristics of Contact-Lens chemical structure inhibits cm3 polymer cm3 STP CO2 gases coefficient for penetrant concentration of penetrant concentration of sorbed Contact-Lens Polymers Contact-Lens Samples Fick's diffusion coefficient Fluoroperm fraction also exhibit gas affinity parameter gas permeability gas population gas transfer glassy polymers Henry's concentration Henry's law highest free-volume fraction inhibits the filling Langley Research Center Langmuir mode concentration lens chemical structure lenses to breathe longest component lifetime lowest Rockwell hardness mass spectrometry mean free-volume cell microvoid radius microvoid volume mode of sorption NASA National Aeronautics Old Dominion University Paraperm 02 penetrant gas dissolved Performing Organization permeability for O2 polarography population in microvoids Positron Lifetime Measurements positron lifetime spectroscopy pressure at solution Research Center Hampton Rockwell hardness number saturation moisture content Services & Materials silicone methacrylate sorbed gas Space Administration space commercialization program test samples trapped in microvoids Upchurch Virginia volume percent