Mechanisms of Conductivity Change in Polymer-Based Gas Sensors

It is important that all indicated devices can function at room temperatures. This means that polymer-based sensors have low power consumption (of the order of microwatts) because no heater element is required for their operation. Properties of polymers that influence the operating parameters of sensors can be physicochemical, chemical, optical (photo- and electroluminescence, optoelectronic), redox, hydrophobic/ hydrophilic, piezoelectric/pyroelectric, and electrical (conductivity, resistivity). Moreover, the polymer itself can be modified to bind biomolecules to a biosensor (Mulchandani and Wang 1996). It is mentioned above that polymers have considerable potential for fabrication of multisensing arrays required for e-nose fabrication (Janata and Huber 1985). 

We need to say that insulating polymers, in which all four valence electrons of carbon are used up in covalent bonds, can also be applied in gas sensor design. Moreover, experiment has shown that, for several types of gas sensors such as capacitive sensors (see Chip. 16 [Vol. 1]) and resistive sensors based on composite materials (Chap. 13 [Vol. 2]), the application of insulating polymers is actually preferable. 

3 Mechanisms of Conductivity Change in Polymer-Based Gas Sensors 

PAni is a special conducting polymer since its doped state can be controlled by acid-base reactions. This effect is widely used to detect acidic and basic gases, in particular ammonia gas, because when exposed in ammonia gas, PAni undergo dedoping by deprotonation (Jin et al. 2001 Hu et al. 2002 Bai and Shi 2007). The mechanism of this interaction is shown in Fig. 3.10. 

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