The development of fiber-optic chemical sensors based on porous optical fibers and sol-gel immobilization techniques

The goal of research described in this thesis has been to explore new materials processing for the development of novel fiber optic chemical sensors. The sol-gel process and the Vycor process have successfully been employed and combined to prepare fiber optic chemical sensors for both vapor phase and liquid phase measurements. Porous glass optical fibers prepared by Vycor process were used as the substrate for selected chemical indicators which were immobilized on the glass surface. The sol-gel process offered a generic way to trap organic indicators in a silica cage structure and the gel itself was coated on the porous glass fibers.; The porous glass optical fibers were prepared by drawing and subsequently heat treating borosilicate glass fibers to promote phase separation. Subsequent leaching out of the boron-rich phase produced a three-dimensional interconnected porous structure which served as a host for a variety of chemical indicators. Absorption of light passing through the porous glass fiber produced a significantly higher sensitivity than devices which rely on evanescent surface absorption. The utilization of a moisture-sensitive indicator CoSO{dollar}sb4{dollar} in conjunction with the porous glass optical fibers has resulted in the development of the first high temperature fiber optic moisture sensor capable of operating at temperatures up to 300{dollar}spcirc{dollar}C.; In addition, a sol-gel derived organic/inorganic hybrid glass film successfully coated on the porous glass fibers has been proven to be chemically stable and durable. The optical properties of the hybrid glass have been investigated. Synthesis of the new sol-gel material and its application to fiber optic sensors have been studied. In particular, a fiber optic pH sensor based on the combination of sol-gel coating technique and Vycor process has been developed for the first time.; For both of the moisture and the pH sensors, important parameters including sensitivity, response time, stability, reversibility and temperature dependence have been investigated.