Ethanol vapor sorption

Fig. 7.9 Resistance response of nontemplated and DG-structured PPy gas sensors to different alcohol vapors and purging with dry nitrogen. Nitrogen was used as carrier gas. Equation 7.3, describing the sorption model, was used to calculate the blue fitting curves, a Nontemplated film, 11 % methanol vapor, b Nontemplated film, 4% ethanol vapor, c DG-structured film, 1% ethanol...

Datta and coworkers measured the sorption of methanol from vapor by Nafion all over the range of methanol activities at 25 °C [274] and 30 °C [275]. The uptake of ethanol and propanol from vapor by Nafion as a function of the alcohol activities were determined at 20 °C [272] and 30 °C [276]. Zhao et al. [281] reported uptake of methanol and ethanol by Nafion, at 40 and 60 °C, up to alcohol activities close to unity. 

Methanol and ethanol treatments do drastically increase the baseline resistance, which could be caused by the swelling of the polymer inhibiting the charge transfer between the conducting particles. Swelling can be permanent due to only partially reversible sorption of the treatment solvent at room temperature (therefore, the treatment also inhibits the response to the corresponding vapor). The remaining methanol or ethanol could, due to the polar character of these solvents, also be an explanation for the enhanced water response. 

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