Graduation Year


Document Type




Degree Name

MS in Materials Science and Engineering (M.S.M.S.E)

Degree Granting Department

Chemical Engineering

Major Professor

Venkat R. Bhethanabotla, Ph.D.

Committee Member

Scott Campbell, Ph.D.

Committee Member

John Kuhn, Ph.D.


QCM, SAW, polymer film, sorption, frequency shift


Benzene, toluene, ethylbenzene, and xylene are classified as volatile organic compounds (VOC), which if present at higher concentrations can cause acute and/or chronic health effects. To protect people from VOCs, the occupational safety and health agency (OSHA) established short term and eight-hour workday exposure limits. The short time levels of exposure for BTEX materials are 5 ppm, 150 ppm, 125 ppm, and 150 ppm, for benzene, toluene, ethylbenzene, and xylene respectively. The eight-hour workday exposure for these same materials are 1 ppm for benzene, 200 ppm for toluene, 100 ppm for ethylbenzene and 100 ppm for xylene. Although there are several laboratory instruments, for example GS, MS, PID, that are used for measuring these materials in a laboratory environment. This work shows that acoustic wave sensors should also be considered for monitoring, detecting, and measuring these types of materials. The sensors are not only sensitive, reliable, and easy to operate, but they are also suitable for providing real time measurements.For this thesis work we used a quartz crystal microbalance (QCM) coated with a polymer solvent, and diluted setup that allowed us to successfully detect approximate 500 ppm of these analytes in a gas phase. In our apparatus system, a controlled amount of BTEX was released into a nitrogen flow stream that brought the mixture of Nitrogen and BTEX to the sensor. The concentration of analytes was controlled through a gastight syringe attached to a syringe pump. The nitrogen flow was controlled by a LabVIEW program and mass flow controller. The presence of the plasticizer in the polymer coating increased the sensitivity of the sensor to the tested analytes. We will also show a design of a surface acoustic wave (SAW) test device capable for gas sensing. Using this fixture and a SAW sensor with Rayleigh waves and a polymer coated delay line, we were able to detect 55 ppm of benzene in a gas phase.