title: Refractometric discrimination of void-space filling and swelling during vapour sorption in polymer films.
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.
authors.affiliation: University of Durham, Department of Physics, South Road, Durham, UK DH1 3LE.
authors.forename: G H
authors.initials: GH
authors.lastname: Cross
authors.forename: Y
authors.initials: Y
authors.lastname: Ren
authors.forename: M J
authors.initials: MJ
authors.lastname: Swann