(484i) Investigation of Polymer-Plasticizer Blends for BTEX Sensing Using Acoustic Wave Devices

Volatile organic compounds (VOCs) are chemicals which evaporate easily and become gases at ambient temperature and pressure. The EPA has made the monitoring of VOCs mandatory due to their health impacts, which range from headaches and nausea to cancer. The current techniques used for VOC monitoring such as photo ionization, gas chromatography, mass spectroscopy, and e-noses sensors are expensive, time-intensive, demand rigorous sample preparation and cannot quantify the VOCs in the air. To employ the shortcomings of current sensor systems, quartz crystal microbalance (QCM) and surface acoustic wave (SAW) sensors based on polymer-plasticizer thin films have been developed. Acoustic wave devices are capable of detecting very low concentrations (ppm, ppb) of organic compounds in the environment. Imprinted polymers as sensing film have been used to detect BTEX gas analytes to a lower limit of 0.5ppm using SAW devices.

Traditionally, the sensitivity and performance of rubbery polymers towards hydrocarbon sensing are superior to glassy polymers however, they show low molecular selectivity due to their amorphous nature, availability of large free volume elements, and display of undesirable viscoelastic effects. Plasticization helps to modify the chemical and physical properties of the glassy polymer by decreasing the glass transition temperature, altering the pore dimensions and increasing the free volume of the polymer film thus enabling higher diffusion and sorption of the analyte molecules. This work shows that the selectivity and sensitivity of glassy polymers can be tailored by introducing a plasticizer. Poly (ethyl methacrylate) (PEMA), Poly (methyl methacrylate) (PMMA), PEMA-PMMA, PMMA-Polystyrene copolymers were modified by introducing plasticizers, diisononyl cyclohexane-1, 2-dicarboxylate (DINCH), diisooctyl azelate (DIOA), dibutyl sebacate (DBS), n-butyl stearate (BS), and di-n-butyl phthalate (DBP) to enhance BTEX sensitivity and selectivity in presence of interferants.

The objective of this study is to investigate the effect of various plasticizers on glassy polymers sensitivity by unraveling the polymer-plasticizer transient response mechanism and identifying the accurate plasticizer for superior BTEX sensing. This work demonstrates that the incorporation of suitable plasticizers into a polymer-based sensor can vastly improve the selectivity for BTEX compounds based on properties such as sorption (via thermodynamic partition coefficients), saturation dynamics, stability, and viscoelasticity of the film. A mathematical model will be incorporated to select the optimum polymer-plasticizer blend for BTEX sensing in gas and liquid phase using QCM and SAW devices.