Optical properties of sulfonephthalein dyes entrapped within polymer matrices for quantification of ammonia vapour and humidity in air

Abstract

We show that the absorbance of sulfonephthalein dye-polymer composite thin films is dependent upon changes in humidity and ammonia concentration. The absorbance at ca. 470 nm increases with humidity for the neutral polymer composite. The acid–base equilibrium reaction of bromophenol blue entrapped within a vinylpyridine–styrene copolymer is applicable to optochemicai humidity sensors. For the Nafion composite, humidification induces a decrease in absorbance in the range 500–600 nm and an increase in absorbance at ca. 440 nm. The absorbance at ca. 600 nm increases with ammonia concentration for the neutral-polymer composite. The response behaviour and reproducibility are also improved by humidification. The sensitivities of the polymer composite to the humidity and ammonia vapour are influenced by the dye substituents and polymer species.