ARRAY-BASED VAPOR SENSING USING CHEMICALLY SENSITIVE, CARBON BLACK-POLYMER RESISTORS

We describe herein the construction of a simple, low-power, broadly re sponsive vapor sensor. Carbon black-organic polymer composites have be en shown to swell reversibly upon exposure to vapors. Thin films of ca rbon black-organic polymer composites were deposited across two metall ic leads, and swelling-induced resistance changes of the films signale d the presence of vapors, To identify and classify vapors, arrays of s uch vapor-sensing elements were constructed, with each element contain ing the same carbon black conducting phase but a different organic pol ymer as the insulating phase. The differing gas-solid partition coeffi cients for the various polymers of the sensor array produced a pattern of resistance changes that can be used to classify vapors and vapor m ixtures. This type of sensor array resolved common organic solvents? i ncluding molecules of different classes (such as aromatics from alcoho ls) as well as those within a particular class !such as benzene from t oluene and methanol from ethanol). The response of an individual compo site to varying concentrations of solvent was consistent with the pred ictions of percolation theory. Accordingly, significant increases in t he signals from array elements were observed for carbon black-polymer composites that were operated near their percolation thresholds.