Comparisons of Polymer/Gas Partition Coefficients Calculated from Responses of Thickness Shear Mode and Surface Acoustic Wave Vapor Sensors

Abstract

Apparent partition coefficients, K, for the sorption of toluene by four different polymer thin films on thickness shear mode (TSM) and surface acoustic wave (SAW) devices are compared. The polymers examined were poly(isobutylene) (PIB), poly(epichlorohydrin) (PECH), poly(butadiene) (PBD), and poly(dimethylsiloxane) (PDMS). Independent data on partition coefficients for toluene in these polymers were compiled for comparison, and TSM sensor measurements were made using both oscillator and impedance analysis methods. K values from SAW sensor measurements were about twice those calculated from TSM sensor measurements when the polymers were PIB and PECH, and they were also at least twice the values 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 were in agreement with each other and with independent data when the polymer was PBD. Similarly, K values from the PDMS-coated SAW sensor were not much larger than values from independent measurements. These results indicate that modulus effects were not contributing to the SAW sensor 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 device or independent measurements, and the impedance analyzer results indicated that this sensor using our sample of PDMS at the applied thickness did not behave as a simple mass sensor. Differences in behavior among the test polymers on SAW devices are interpreted in terms of their differing viscoelastic properties.

Analysis of Liquid-Phase Chemical Detection Using Guided Shear Horizontal-Surface Acoustic Wave Sensors

“…The contribution of mass loading to the sensor response is well accepted in this field while the contribution of the viscoelastic property of polymer coating is still under investigation, even in gasphase sensors. 18,19,[25][26][27] Unfortunately, results in gas phase cannot be totally adapted or used to explain liquid-phase responses. For example, ongoing work in liquid-phase sensing has also shown that for a rubbery polymer such as PDMS viscoelasticity changes can clearly dominate sensor response.…”

“…This is consistent with reported amplification factors due to viscoelastic effects that are reported in the literature for gas-phase sensing, which are in the range of 2−4. 18,19,[25][26][27] Figure 6 Selectivity comparison of 0.64-μm PIB-coated guided SH-SAW sensor platform in the detection of toluene, xylenes, and ethylbenzene in DI water. -is the simulation result using predicted added mass loading and incremental viscoelastic changes based on experimental loss data.…”

ATR-FTIR spectroscopic analysis of sorption of aqueous analytes into polymer coatings used with guided SH-SAW sensors

“…(1) is often insufficient for predicting the magnitude of sensor response [29][30][31][32][33]. Positive frequency shifts have also been observed for SAW devices coated with PDMS films and exposed to selected gas phase analytes [34][35][36].…”

Solvation, transduction and independent component analysis for pattern recognition in SAW electronic nose

“…Taking m P /m A ≈ 500 (approximately the degree of polymerization) and γ = 1 we obtain m SAW = 1-7. For several analyte-polymer pairs the experimentally reported values are m SAW = 1.5-3.45 [32,34,35,37].…”

“…(7) appears similar to the linear solvation energy relationship (LSER) for modeling vapor-polymer interaction under infinite dilution [3,29]. The LSER model has been widely used to explain equilibrium partition coefficients in gas-liquid chromatography (GLC), thermogravimetry (TG), and quartz crystal microbalance (QCM) and surface acoustic wave (SAW) sensing experiments [30][31][32][33][34][35]. In this model, each interaction term on the right of Eq.…”