COMPARISONS OF POLYMER GAS PARTITION-COEFFICIENTS CALCULATED FROM RESPONSES OF THICKNESS-SHEAR MODE AND SURFACE-ACOUSTIC-WAVE VAPOR SENSORS/

Apparent partition coefficients, K, for the sorption of toluene by fou r different polymer thin films on thickness shear mode (TSM) and surfa ce acoustic wave (SAW) devices are compared, The polymers examined wer e poly(isobutylene) (PIB), poly(epichlorohydrin) (PECH), poly(butadien e) (PBD), and poly(dimethylsiloxane) (PDMS), Independent data on parti tion coefficients for toluene in these polymers were compiled for comp arison, and TSM sensor measurements were made using both oscillator an d impedance analysis methods, K values from SAW sensor measurements we re about twice those calculated from TSM sensor measurements when the polymers were PIB and PECH, and they were also at least twice the valu es of the independent partition coefficient data, which is interpreted as indicating that the SAW sensor responds to polymer modulus changes as well as to mass changes, K values from SAW and TSM measurements we re in agreement with each other and with independent data when the pol ymer was PBD, Similarly, K values from the PDMS-coated SAW sensor were not much larger than values from independent measurements, These resu lts indicate that modulus effects were not contributing to the SAW sen sor responses in the cases of PBD and PDMS, However, K values from the PDMS-coated TSM device were larger than the values from the SAW devic e or independent measurements, and the impedance analyzer results indi cated that this sensor using our sample of PDMS at the applied thickne ss did not behave as a simple mass sensor, Differences in behavior amo ng the test polymers on SAW devices are interpreted in terms of their differing viscoelastic properties.