Graduation Year


Document Type




Degree Name

MS in Chemical Engineering (M.S.C.H.)

Degree Granting Department

Chemical Engineering

Major Professor

Venkat Bhethanabotla, Ph.D.

Co-Major Professor

Scott Campbell, Ph.D.

Committee Member

John Kuhn,Ph.D.


copolymer, plasticizer, sorption, thermodynamics


Detection of volatile organic compounds (VOC’s) in the environment is important for human health and wellness. Long term exposure of certain VOC’s like benzene, toluene, ethylbenzene and xylene (BTEX) has a severe effect on human health. There are techniques such as gas chromatography, photo ionization, and mass spectroscopy that are time consuming, require gas sampling and are ineffective in real time sensing in air. Acoustic wave devices such as surface acoustic wave (SAW) devices can be used for sensing BTEX compounds in both vapor and liquid phase. The quartz crystal microbalance (QCM) is a low-frequency acoustic wave device, which can be used to characterize polymer film sensing quickly and easily by studying the sorption properties of BTEX compounds in them. In this work, thin films (~ 0.5 microns) of polymer/plasticizer blends are spin-coated on a 5MHz QCM for the detection of VOC’s. A polymer/plasticizer combination of poly (ethyl methacrylate) (PEMA) and a copolymer of poly (ethyl methacrylate) and poly (methyl methacrylate) (PEMA/PMMA) with di n-butyl phthalate (DBP), di-n-butyl sebacate (DBS) and n-butyl stearate (BS) are used for the detection of benzene, toluene and ethylbenzene in vapor phase. The working apparatus consists of a stream of solvent vapor diluted with nitrogen to an arbitrary concentration passing over the QCM oscillated to its resonant frequency. The sorption data are reported at 298.15 K in terms of activity as a function of weight fraction curves and are interpreted with the Flory-Huggins ternary model. The addition of plasticizer modifies the free volume properties of the polymer, thereby increasing diffusion and sensitivity of BTEX vapors. The plasticizer composition is tailored to 17.5%, for maximum sorption with minimal viscoelastic effects. The sorption and sensitivity of BTEX are interpreted and studied in terms of plasticizer type and concentration.