An investigation into the use of electrochromic polymers in optical fibre gas sensors

A gas sensor based on the incorporation of electrochromic polymers into a fibre-optic device is described. The optical changes that occur when poly(4,4′-diphenylaminep-heptyloxy)benzylidene (PDPAHB) and poly(4,4′-diphenyliminep-heptyloxy)benzylidene (PDPIHB) are exposed to different relative humidites (RH) or various ammonia concentrations (at 23°C) have been investigated. Results of the exposure of the two polymers to 0–100% relative humidity show that the working range is between 50 and 100% RH. Reversal of the films was possible by flushing with dry air. Exposure of the two polymers to increasing ammonia concentrations results in a decrease in absorbance measured at 430.46 nm for PDPAHB and at 575.78 nm for PDPIHB. Reversal of the optical changes that occurred in both films due to the presence of ammonia, was not successful by flushing with dry air or HCl, respectively.