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Further Development of Conductometric Sensors for Organic Vapours Based on Organic Semiconductive Thin Films

Further development of conductometric sensor for organic vapours based on organic semiconductive thin polymer films was undertaken. Previous searches showed that this kind of sensors has a great potential. The sensor response in respect to the ethanol concentration was shown to be highly linear on all types of electrodes [1] (4 point - P, 4 track - T, Quad - Q, Dual - D). All the electrodes had the junction resistance higher than polymer resistance. P electrode has shown to be the most problematic and unstable, and had the biggest fraction of junction resistance in total resistance. Q type electrode has shown to be the most sensitive one, and had the lowest absolute values of resistance, i.e. the highest conductivity. T and D electrodes had the best repeatability, good sensitivity and behaved similarly. Experimental setup remained the same, as presented before. To investigate how number of spin-coated Poly(3, 4-ethylenedioxythiophene)-poly(styrenesulfonate) or PEDOT-PSS films influences the behaviour of the sensor, electrodes with one and three layers of film were compared. Electrodes with three layers of polymer film were shown to be more stable and with better repeatability. However, for stabilization of sensor response longer period of time was needed. All the electrodes with three layers had about 10% smaller fraction of junction resistance in total resistance. In order to find the bottleneck of the process dynamic responses of sensors were recorded. With air stirring, the sensors response achieved stabilization two to four times quicker compared without air stirring. Exposing the sensor directly to ethanol vapours, without evaporation process, few times quicker response stabilization resulted, compared to evaporation process with air stirring. From these experiments it can be concluded that mass transfer trough boundary layer between liquid ethanol and bulk of air is the bottleneck of the process. This was confirmed with a mathematical model, too.

conductometric sensor; organic vapours; semiconductive polymer film

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