Date of Award
Program or Major
Doctor of Philosophy
W Rudolf Seitz
Poly (4-vinyl pyridine) particles produced by dispersion polymerization were suspended in a hydrogel membrane and used for remote measurements employing fiber optic sensors. The refractive index of poly(4-vinyl pyridine) particles is higher than the refractive index of the hydrogel. At low pH, protonation of the poly(vinyl pyridine) causes the particles to swell reducing their refractive index and lowering membrane turbidity. The membrane response to pH was monitored using instrumentation originally that was constructed by Michael Civiello and was further developed in this work. A new hydrogel, HYPAN, was evaluated as the medium in which the particles are suspended. Methods for attaching a polymer layer to the distal end of an optical fiber were also examined.
A 1310 nm wavelength source and an InGaAs detector were installed in the remote sensing instrument to improve signal quality by lowering the noise associated with the signal. The noise associated with the instrument response results from two sources, one being Rayleigh scattering of the laser pulse as it travels down the optical fiber. The other contribution to the background is the reflection from the optical fiber connector/polymer interface at the distal end of the optical fiber. The use of longer wavelength source compared to 834 nm reduced the background signal. The noise associated with the signal at the longer wavelength, however, is increased compared to the original, 834 nm. The use of angled connectors in the instrument reduced the background of the signal and enhanced the turbidity signal by a factor of three.
Using and improving the instrumentation designed for remote optical sensing, it was possible to detect pH changes through 500 meters of optical fiber. The particles produced from 4-vinyl pyridine showed quick response times and relatively large changes in response when placed in a HYPAN membrane. The pKa of these particles was determined to be approximately 4.6 through 500 meters of fiber. Sensors were constructed on the top of an optical fiber connector, because we could not develop a convenient method for attaching a polymer layer on the distal end of an unconnectorized optical fiber.
Milde, Siobhan P., "Remote optical fiber sensing based on reflectance due to the swelling of polymer particles produced by dispersion polymerization" (2001). Doctoral Dissertations. 23.