There are many different ways of reporting the response time of a gas sensor. Whether it's t90 or t50 (the rise time to 90% of final value or the rise time to 50% of final value), they all refer to an EQUILIBRIUM state (aka final value), where the response (vs. time) reaches a plateau and does not change significantly over time. However, such equilibrium never occurs in many cases. For example, we are working with various polyaniline-based ammonia vapour sensors; we do see a rapid rise of resistance even in exposure to sub-ppb level concentrations, but we rarely see a plateau of response even after several hours.
What parameters in the sensing film itself do govern the response speed? Apart from that, is there any instrumental parameter influencing? (gas flow characteristics, sensing chamber, size, ...)
Gas flow characteristics is important, however you use a organic materials for gas sensing application. Then the mechanism involved in gas detection is important.
Amount of adsorption which is affected very significantly by surface area of organic material( Since there is very dangling bonds in surface of organic materials) which means adsorption in surface is not most of the time uniform. The temperature is very important and you need to know the process is physical adsorption (physisorption) or chemical adsorption (chemisorption). and finally for resistive gas sensors (I-V) you need discuss space charge layer which affected by gas adsorption either for capacitive type gas sensors.
Gas flow rate, operating temperature and chamber size will have strong influence on response/recovery rates. In addition, the thickness of sensing layer, its microstructure (having more pores or not) will also influence the response/recovery rates.
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