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Towards all-polymer surface acoustic wave chemical sensors for air quality monitoring Man, Gabriel

Abstract

Volatile organic compounds (VOCs) are a precursor to the formation of ground-level ozone and airborne particulate matter, both of which are hazardous to human health. Currently in Canada, other air pollutants such as ozone and nitrous oxides are measured by an air quality monitoring network in real-time, while VOCs are collected in canisters and sent to a central laboratory for analysis. This is a time-consuming and non real-time method, and due to the spatial variability of air pollution, many points of measurement are needed. A distributed point sensor network could address the resolution and real-time challenges, but would impose an added operating expenditure burden on air quality monitoring agencies. Low-cost, yet sensitive chemical sensors could contribute to lowering operating expenditures of a network’s sensing units over the installed lifetime of the units. The objective of this work was to lay the groundwork for a sensing platform from which low-cost yet sensitive chemical sensors can be developed. The sensing platform is an all-polymer surface acoustic wave (SAW) device, and the materials selected for its fabrication are Polyvinylidene Fluoride (PVDF) for the sensor substrate and Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) for the interdigital transducer electrodes. In this work, an apparatus and a process for preparing piezoelectric PVDF film was developed. PVDF-based resonators were successfully demonstrated. In addition, repeatable processes for inkjet micropatterning highly electrically conductive PEDOT:PSS electrode tracks on PVDF were developed for three inkjet nozzle orifice sizes (20, 30, 40 µm). For tracks micropatterned using the same process, the electrical resistances have a standard deviation of 8.5% of the average. The electrical conductivity of micropatterned tracks is approximately 150 S/cm, or one-sixth of the manufacturer’s claimed bulk film conductivity. Using the 30 µm nozzle, the smallest electrode track width that can be micropatterned repeatably is 75 µm. A track width of 55 µm was achieved using the 20 µm nozzle.

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