Development of a SAW poly(epichlorohydrin) gas sensor for detection of harmful chemicals.

The uniformity and compactness of the surface of a viscoelastic sensitive film are among the most important factors that influence the characteristics of a surface acoustic wave (SAW) gas sensor, directly affecting the detection sensitivity of a SAW sensor on a target gas. In this paper, poly(epichlorohydrin) (PECH) with viscoelastic properties was used as sensitive film for the detection of 2-chloroethyl ethyl sulfide (CEES), a common simulant of the chemical agent mustard gas. Nanoscale films were prepared using a spin coating technology on a SAW delay line of 200 MHz. Films were evaluated using polarizing microscopy and atomic force microscopy and observed with uniform surface states and particle diameter in the cluster region of 4.52-5.22 μm. The interface parameters, including contact angle, surface tension, Gibbs free energy, work of adhesion, work of immersion, and spreading coefficient values were 9.31° to 39.63°, 22.475 to 29.945 mN m-1, -85.70 to -78.08 J m-2, 78.08 to 85.70 J m-2, -42.62 to -35.00 J m-2, and 0.46 to 8.08 J m-1, respectively. These values were obtained by experiments combined with the Young T equation and Gibbs adsorption isotherm, and the surface analysis was carried out theoretically. The glass transition temperature (-22.4 °C), viscosity, pyrolysis, and other physical characteristics of the prepared PECH were discussed. Five SAW sensors prepared at the same time were used to test the repeatability of CEES measurements at one concentration, where the consistency of the sensor preparation was confirmed. At a concentration of 13.6 mg m-3 for CEES, 10 consecutive detection results showed good repeatability (i.e., standard deviation = 0.295, coefficient of variance = 0.021, and population mean deviation = 0.364). At room temperature (20 °C ± 5 °C), different concentrations of CEES were detected using the developed sensor, which showed good linearity in the concentration range of 1.9-19.6 mg m-3 (y = 0.0309 + 1.13x, r = 0.99478). The limit of detection was 0.85 mg m-3, the limit of quantitation was 1.91 mg m-3, and the sensitivity of the SAW sensor was 1.13 mV (mg m-3). The adsorption mechanism related to PECH in the detection of CEES was also discussed.