Refractometric discrimination of void-space filling and swelling during vapour sorption in polymer films |
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Authors: | Cross G H Ren Y Swann M J |
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Institution: | University of Durham, Department of Physics, South Road, Durham, UK DH1 3LE. |
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Abstract: | Thin polymeric films have been deposited as upper cladding layers on a new integrated optical interferometer fabricated from layers of silicon oxynitride on a silicon wafer. The evanescent field of the probing waveguide mode transduces refractive index changes in the polymer layer into the measured phase changes in the device. Real-time measurement of index change and its sign is obtained. Upon exposure to humid air, we record water sorption by films of poly(vinyl pyrrolidone) by a rapid positive index change for void-space filling followed by a slow negative index change for swelling. Sorption of water vapor into a thin film of the viscous liquid polymer polyethylenimine shows only swelling mode behaviour and a simple constitutive model can be applied to give the fractional water occupied volume. |
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