Gas detection using polymeric light-guiding films

摘要

Abstract: Upon diffusion of vapors in polymeric materials these change their optical properties in various forms. First, in diffused e.g. water increase the density and therefore the refractive index, due to the Lorentz Lorenz Equation. Second, in polymers with a high stress optical coefficient, birefringence can be detected. It occurs because of the swelling of such a material. Together with a fixed interface to a substrate clamped film, this leads to mechanical stress and therefore to birefringence. Depending on the choice of the polymer, one of these effects is dominant or can be neglected. In both cases however, it is possible to determine e.g. the humidity of the air or the concentration of other organic vapors in a certain gas flow. The behavior of such materials in contact to humid or other atmospheres is measured by wave guide techniques and ATR-spectroscopy. Both methods allow to realize real-time monitoring or online measurements.!6