EFFECTS OF FILM MORPHOLOGY ON THE FREQUENCY AND ATTENUATION OF A POLYMER-COATED SAW DEVICE EXPOSED TO ORGANIC VAPOR

The frequency and attenuation of PIB polymer-coated SAW devices were monitored during exposure to isooctane vapor as the coating thickness on the SAW was varied incrementally up to film thicknesses of about 300 kHz. Airbrush-coated devices exhibited significantly different response behavior compared to drop evaporation coated devices, most notably in attenuation of the acoustic wave. The drop evaporated films exhibited periodic, large attenuation with concurrent decreases in observed frequency shifts. These results are consistent with the film resonance model of Martin and Frye. In this work, we demonstrate how this model can also be used to estimate the shear modulus of polymer films exposed to vapors. For the PIB films used in this work exposed to isooctane vapor the resonance thickness is calculated to be 0.0082 mum (before swelling), with a calculated modulus of 2.7 X 10(5) dynes/cm2. This represents a significant decrease in modulus compared to a neat PIB film (not exposed to vapor) and supports recent reports on the Importance of polymer swelling in SAW responses.