The Fractional Free Volume of the Sorbed Vapor in Modeling the Viscoelastic Contribution to Polymer-Coated Surface Acoustic Wave Vapor Sensor Responses
- BATTELLE (PACIFIC NW LAB)
- Michigan, Univ Of - Ann Arbor
Surface acoustic wave (SAW) vapor sensors with polymeric sorbent layers can respond to vapors based on mass-loading and modulus decreases of the polymer film. The modulus changes are associated with volume changes that occur as vapor is sorbed by the film. A factor based on the fractional free volume of the vapor as a liquid has been incorporated into a model for the contribution of swelling-induced modulus changes to observed SAW vapor sensor responses. In this model, it is not the entire volume added to the film by the vapor molecules that causes the modulus to decrease. The free volume effect is calibrated from thermal expansion experiments. The amplification of the SAW vapor sensor response due to modulus effects that are predicted by this model have been compared to amplification factors determined by comparing the responses of polymer-coated SAW vapor sensors with the responses of similarly-coated thickness shear mode (TSM) vapor sensors, the latter being gravimetric. Results for six vapors on each of two polymers, poly(isobutylene) and poly(epichlorohydrin), were examined. The model correctly predicts amplification factors are related to the specific volume of the vapor as a liquid. The fractional free volume factor provides a physically meaningful addition to the model and is consistent with conventional polymer physics treatments of the effects of temperature and plasticization on polymer modulus.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 15001343
- Report Number(s):
- PNNL-SA-32297; NN2001000; TRN: US200404%%32
- Journal Information:
- Analytical Chemistry, Vol. 72, Issue 13; Other Information: PBD: 1 Dec 1999
- Country of Publication:
- United States
- Language:
- English
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