Development of a lifetime-based fiber optic imaging sensor to study water transport in thin Nafion membranes

摘要

Fiber-optic chemical sensors (FOCS's) are useful for making remote, in-situ, and microscale measurements. Many intensity-based and lifetime-based FOCS's have been developed for a wide range of properties and analytes. Most of these sensors give only a single-point measurement however, recently a few intensity based imaging FOCS's have been described. We have developed intensity-based fiber- optic imaging systems to measure the transport of water in thin Nafion$+TM$/ membranes and to monitor the development of pH gradients at the surface of an electrode during electrolysis of water. However, intensity-based measurements are difficult to calibrate because of the dependence of luminescence intensity on many interfering factors including dye concentration and varying excitation intensity. As a result, we are developing lifetime-based fiber-optic imaging sensors for a variety of applications. At this point we have measured a lifetime image across a sol-gel crack using a fiber-optic image guide to carry the excitation light to the sample and the resulting luminescence image to an ICCD. Currently, we are testing an oxygen imaging FOCS to capture lifetime-based images of at least two different lifetimes. This paper describes the single-point, lifetime-based sensors we have developed as precursors to fiber-optic imaging chemical sensors, the intensity-based imaging studies of water transport in thin Nafion$+TM$/ membranes and the development of pH gradients at electrode surfaces. It also discusses the instrumental system and methods used to collect lifetime images of sol-gel cracks with a fiber- optic, and the preliminary results of our imaging oxygen sensor.