NOVEL THIN OPTICAL FILM SENSORS FOR THE DETECTION OF CARBON-DIOXIDE

New materials are described which enable the indirect optical sensing of carbon dioxide using visible light. These materials, consisting of plasticised polymers in which are dissolved organosoluble salts of acid-base indicator dyes, act as completely reversible and non-consumptive sensors. They may be produced in the form of thin, transparent films, the absorbance of which is strongly influenced by carbon dioxide. These films are completely insoluble in water and contain no volatile component; consequently, they function over a wide range of temperature and relative humidity. The time-dependent and time-independent responses to carbon dioxide of example films are described and factors which influence the response time and stability of the sensor materials are examined and discussed. A mechanism is proposed to explain the responsiveness to carbon dioxide of the indicator dyes in a substantially non-aqueous medium. Sensors may be fabricated which combine subsecond response times with storage lifetimes in excess of 1 year.