Chemically Sensitive Polymer Coatings For SH-Surface Acoustic Wave Sensors for the Detection of Benzene in Water
Date of Award
Master of Science (MS)
Electrical and Computer Engineering
Lee, Chung Hoon
Polymer-coated shear horizontal surface acoustic wave (SH-SAW) sensors are investigated for the detection of benzene in aqueous samples. The SH-SAW sensors using three-layer geometry have a single polymer sensing layer which absorbs the analyte and interacts with the surface wave. Several polymers are identified as potential improvements over current sensing films based on glass transition temperature and Hildebrand solubility parameter. The polymers investigated in this work include poly (methyl acrylate) (PMA), poly (butyl acrylate) (PBA), poly (ethylene co-vinyl acetate) (PEVA), bisphenol-A poly (dimethylsiloxane) (BPA PDMS), and bisphenol-A poly (hexamethyltrisiloxane) (BPA HMTS).
The polymers are spin coated on a lithium tantalate (LiTaO3) SH-SAW dual delay-line device at thicknesses between 0.3 µm and 1.0 µm. Each film's thickness is measured and the film is exposed to multiple concentrations of the aromatic hydrocarbons benzene, ethylbenzene, toluene, and xylenes (BTEX). The added mass and viscoelastic changes in the sensing layer result in a change in center frequency and acoustic loss of the device. The frequency change is measured and used to determine sensitivity of the coated sensor to each analyte.
BPA PDMS and BPA HMTS show larger sensitivities to each of the BTEX analytes than PBA, PMA, or PEVA. However, both BPA PDMS and BPA HMTS were observed to lose sensitivity during the aging process. It is shown that the aging effect on BPA HMTS can be mitigated by baking the film after it is applied to the device.