Enhanced Sensitivity to and Classification of Volatile Carboxylic Acids Using Arrays of Linear Poly(ethylenimine)−Carbon Black Composite Vapor Detectors

Abstract

Vapor detectors formed from composites of conductors and insulating organic polymers have been tailored to produce increased sensitivity toward specific classes of analyte vapors. Upon exposure to acetic acid at 1% of its vapor pressure, detectors consisting of linear poly(ethylenimine) (1-PEI)-carbon black composites showed an approximately 10(3) increase in signal/noise relative to the performance of typical insulating organic polymer-carbon black composite vapor detectors. Compositional diversity in an array of such vapor detectors was obtained by varying the degree of plasticization of the 1-PEI films. The resulting vapor detector array produced sensitive detection of, and robust discrimination between, various volatile organic acids and relatively little response from nonacidic organic vapors or from water vapor. Measurements of the mass uptake, thickness change, and electrical conductivity of such composites indicate that swelling of the polymer film, and thus its normalized resistance response, is beyond that expected by mass uptake alone upon exposure to acetic acid vapor. This additional thickness increase is attributed to charge-induced polymer swelling occurring from polymer-analyte interactions. Electrical percolation also plays a significant role in producing the large increase in normalized resistance response of these composites upon exposure to acetic acid vapor.

Applications and Advances in Electronic-Nose Technologies

“…Protonated carboxylato-terminated and amino-terminated composites showed a ∼10 3 –10 4 increase in sensitivity for detection of volatile amines. Sensitive detection and robust discrimination between various volatile organic acids was achieved with relatively low sensor responses to nonacidic organic vapors or water vapor [214]. The mechanism of enhanced sensor sensitivities towards volatile carboxylic acid vapors were quantified based on relative contributions of electrical percolation effects, increases in analyte sorption, and charge-induced swelling effects of the sorptive polymer films [215].…”

Carbon for Sensing Devices

“…Electronic nose technology, [189] based on polymeric microresistance sensors incorporating CB particles, have been used to discriminate between odorant vapors [190] producing results which qualitatively agree with percolation theory and which have been shown to be sufficiently sensitive to steric and other factors, to be able to discriminate between a range of primary alcohols, [116] and primary, secondary and tertiary alcohols [191]. These sensors have been developed with enhanced sensitivity [190] and used to qualitatively identify odors to which the detection system has not previously been exposed [192] using arrays of host polymer matrices [193].…”

Development of chemiresponsive sensors for detection of common homemade explosives.

“…This swelling causes disruption in the conduction pathways within the elastomer resulting in an increase in the resistivity of the material. In order to differentiate analytes, arrays of chemiresistors made with different elastomers are used and pattern recognition is used to match the sensor responses with known analyte responses [1][2][3][4][5][6][7][8][9][10][11][12]. In addition to the equilibrium sensor response, work has also been performed investigating the kinetic response of chemiresistors when exposed to high vapor pressure materials [13][14][15].…”