An Investigation of Microstructural Characteristics of Contact-lens Polymers

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National Aeronautics and Space Administration, Office of Management, Scientific and Technical Information Division, 1990 - Contact lenses - 8 pages
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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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