Sensor System for Alcohol and Chlorinated Hydrocarbon Vapours on the Basis of Semiconducting Polymers

Abstract

A novel polymer-chemosensor microsystem which can be operated without additional energy consuming heating is presented. Production steps were reduced to metal coating of ceramic plates and structuring of an interdigital array by CAD-supported pulsed laser ablation (PLA) instead of conventional lithographic techniques which yield low production costs only for high production numbers. The active sensor film consists of a semiconducting polymer which can be deposited as a polymer precurser fluid onto the transducer, and can-be tempered in-situ to yield the required polymeric species and chemical functionality. A precurser, poly-2,5-furylene-hydroxy-ethylene, is coated on the pulse-laser processed interdigital array structures on an Al₂O₃ substrate and converted to various poly-2,5-furylene-vinylene (PFV) derivatives by special heat treatments under inert atmosphere. Costly capacitive modulation and lock-in data acquisition techniques were replaced by simple direct current measurements. Certain sensor types exhibited remarkable sensitivity e.g. for 1,1,2-trichlo-roethylene and propanol, but moderate cross sensitivity for humidity. The response time is of the order of few minutes, and the current signal is linear in a wide analyte pressure range. Sensitivities for alcohols and chlorinated hydrocarbons are most probably related to hydrophobic van der Waals interactions whereas Brönstedt acidity or Lewis basicity seem to play minor roles. Electronic or van der Waals interaction leads to deviation of the idealy flat and rigid structure of the conjugated polymer thus allowing for more flexibility of the chains, more intimate inter-chain contacts and higher conductivity.