Date of Award
Master of Science (MS)
Electrical and Computer Engineering
Detection and quantification of benzene, toluene, ethylbenzene, and xylenes (BTEX) in liquid phase is of interest because of the significant public health hazards posed by these compounds. BTEX are volatile organic compounds (VOCs) commonly used as additives in gasoline. Shear horizontal surface acoustic wave (SH-SAW) devices have shown promise in liquid phase sensing applications and is used to address this problem. SH-SAW devices can be made chemically sensitive by depositing a polymer coating on the device surface. SH-SAW devices coated with commercially available polymers have shown modest sensitivity to BTEX compounds. However, there are few polymers which exhibit the properties necessary for BTEX sensing in water. The addition of plasticizer can reduce the glass transition temperature of the polymer, resulting in a blend which is suitable for sensor coatings. Polymer-plasticizer blend coatings have shown high sensitivity to BTEX compounds and as well as partial selectivity to those compounds. High selectivity is desired for more accurate identification and quantification of BTEX compounds, including in samples containing multiple BTEX compounds and other contaminants. Sensor arrays implemented with several appropriate coatings can be used to achieve the desired selectivity. Nine sensor coatings have been developed and characterized for sensitivity and response time constant for BTEX compounds. Coating compositions include 2.5% PIB and 4% PECH polymer solutions and 17.5% DIOA-PS, 23% DINCH-PS, and 22%, 30%, 32%, 33.5%, and 35% DTP-PS polymer-plasticizer blends. Using combinations of these coatings, three arrays have been implemented and analyzed, each composed of five selected sensor coatings. Analysis of arrays formed entirely from polymer-plasticizer blend coatings indicate that highly sensitive and selective arrays can be formed using only these coatings. Results also show that coatings which are not partially selective to ethylbenzene and xylenes can be used to increase coating chemical diversity in arrays without negatively impacting array selectivity. Analysis of the three arrays has been applied to the implementation of a final array to further increase sensitivity and selectivity. Results show that this array has the highest selectivity to BTEX together with the highest sensitivity and coating diversity.
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