Thin Films Of Polymer Carbon Black And Gas Sensing Properties

As the core of the gas sensor, gas sensing materials are developing from single materials to composite materials. Compared to traditional inorganic semiconductor materials, conductive polymer materials have many advantages such as low cost, simple fabrication processing and so on, sensors fabricated by the materials can be operated at room temperature, and they are reversible under normal temperature and pressure. In this thesis,conductivity characteristics and gas sensing characteristics of the conductive polymer/carbon black(CB) composites are studied. Main results of the research are as follow:(1) In order to study the influence of coating dosage, carbon black content, carbon black nature, and polymer matrix type on polymer/carbon black films'conductivity characteristics, a few of poly(2-vinypyridine)/CB films and poly(4- vinyphenol)/CB films were prepared, and their conductivity was measured and discussed. Results showed that the films had the best conductivity characteristics when the coating dosage was 3ul and the composites solution ratio was 1mg/ml. The relationship between poly(2-vinypyridine)/CB composites'conductivity with carbon black content was consistent with the typical percolation theory. Better conductive modified carbon black can be prepared by hydroxymethyl and titanium coupling agent treating original carbon black, percolation threshold value of the composites formed with poly(2-vinypyridine) matrix and modified carbon black decreased significantly, conductivity of the composites enhanced obviously. Due to the dispersion and infiltration of the carbon black in different polymer matrix was different, poly(4-vinyphenol)/CB composites and poly(2-viny- pyridine)/CB composites showed different electrical properties.(2) Four types of poly(2-vinypyridine)/CB films sensors with different components were prepared so as to study the sensors'response to organic solvent vapor. Results showed that sensor 3 prepared by poly(2-vinypyridine) mixed with 10% content carbon black showed the best gas sensing characteristics, its selectivity and stability to the alcohol vapors was the best, also its sensitivity was better. Response and recovery characteristics of sensor 3 to methanol, ethanol and isopropanol were tested, results showed that the response to ethanol was the maximum, the response to methanol was the minimum, additionally, the sensor also show sensitive to humidity.(3) In the experiments, four different components of poly(3-hexiylthiophene)/ carbon black film gas sensors were fabricated, the response to NO2 was tested. Unlike traditional polymer/carbon black composite, when poly(3-hexiylthiophene)/carbon black film gas sensors were exposed to NO2, their electrical resistance decreased. Results suggested that sensor 7 prepared by poly(3-hexiylthiophene) mixed with 5% content carbon black by spin-coating showed the best sensitivity and stability to NO2, also its response linearity was better. Higher carbon black content would reduce the sensitivity of the composites to NO2. Films prepared by spin-coating show the better gas sensing characteristics compared to those prepared by dip-coating. And the incorporation of PdO may reduce the response sensitivity, but can improve its response linearity.