SYNTHESIS AND EVALUATION OF FLUOROPOLYOL ISOMERS AS SAW MICROSENSOR COATINGS - ROLE OF HUMIDITY AND TEMPERATURE

A surface acoustic wave (SAW) organophosphorus gas detector has been d esigned, fabricated and tested. The gas detector consists of a dual de lay line fabricated on a single quartz substrate. Each delay line is c onnected into the feedback path of a radio-frequency amplifier, to rea lize a SAW oscillator. The propagation path of one delay line is coate d with fluoropolyol (FPOL). These polymers offer an interesting way to detect organophosphorus compounds like GB at low concentration levels . The absorption of vapors induces phase variations due to mass loadin g and stress effects. These variations result in corresponding frequen cy shifts. In this work, we have synthesised the four FPOL isomer comb inations separately and characterized these materials by physico-chemi cal analysis. A series of SAW sensors have been coated with these mate rials and experimental results as a function of vapor concentration ar e presented. The influence of coating thickness, temperature and humid ity are examined. Results showed on one hand that frequency variations are linear with GB gas concentrations from 0.5 to 10 ppm and on the o ther hand that sensitivity to organophosphorus compounds is two times greater in wet atmospheres (RH = 60%) than in dry air. The sensitivity was also better at a working temperature close to the glass transitio n point (T-G) of the polymer. Above T-G, the modification of the polym er structure induced a great radiation of the acoustic energy in the c oating. (C) 1998 Elsevier Science S.A. Al rights reserved.