Examination of mass and modulus contributions to thickness shear mode and surface acoustic wave vapour sensor responses using partition coefficients

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Abstract
New data are reported on vapour sorption by four different polymer thin films on thickness shear mode (TSM) and surface acoustic wave (SAW) devices. The polymers examined were poly(isobutylene), PIB, poly(epichlorohydrin), PECH, poly(butadiene), PBD, and poly(dimethylsiloxane), PDMS. The test vapours for the TSM sensor experiments were benzene, toluene, hexane, cyclohexane, chloroform, dichloromethane, carbon tetrachloride and butan-2-one, tested at several concentrations from P/P0=ca. 0.03 to 0.64. Measurements on the TSM devices using oscillators were complemented with measurements by impedance analysis. Acoustic wave sensor data were converted to apparent partition coefficients calculated assuming the response was due to mass-loading only. Values derived from SAW and TSM measurements were compared with one another, and with other partition coefficient data determined by non-acoustic wave techniques. It was found that TSM devices coated with PIB, PECH, and PBD (film thickness ca. 50% of the SAW response. The responses of PBD and PDMS-coated SAW devices were not enhanced relative to the expected mass-loading responses. Differences in behaviour among the test polymers on SAW devices are discussed in terms of the differing viscoelastic properties of these materials.

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