ar6 - Temperature effects on polymer-carbon composite...

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Temperature effects on polymer-carbon composite sensors: evaluating the role of polymer molecular weight and carbon loading M.L. Homer, J.R. Lim, K. Manatt, A. Kisor, A.M. Manfreda, L. Lara, A. D. Jewell, S. -P.S.Yen, H. Zhou, A. V. Shevade and M.A.Ryan Jet Propulsion LaboratoryKalifomia Institute of Technology 4800 Oak Grove Drive, Pasadena, CA 91 109 USA mhomer(iimail1 .iol.nasa.nov, [email protected], [email protected], akisort3maill .iol.nasa.eov, Allison.M.Manfreda@.iol.nasa.eov, [email protected], aiewell@"l1 .id.nasa.rov, [email protected], [email protected], [email protected], mrvan@,iol.nasa.eov Abstract We report the effect of temperature coupled with varying polymer molecular weight and carbon loadings on theper- formance ofpolymer-carbon black composite films, used as sensing media in the JPL Electronic Nose (ENose). While bulk electrical properties of polymer composites have been studied, with mechanisms of conductivity described by con- nectiviry and tunneling, it is notfilly understood how envi- ronmental conditions and intrinsic polymer and filler properties affect polymer composite sensor characteristics and responses. Composites of polyethylene oxide (PE0)- carbon black (CB) considered here include PE0 polymers with molecular weights 20K. 600 K and IM. The effects of polymer molecular weight on the percolation threshold of PEO-carbon composite and incremental sensor tem- perature eflects on PEO-carbon sensor response were in- vestigated. Results show a correlation between the polymer molecular weight and percolation threshold. Changes in sensor properties as a function of temperature are also observed at dyerent carbon loadings; these changes may be explained by a change in conduction mechanism. Keywords Polymer-composite, Electronic Nose, Temperature, Con- duction mechanism INTRODUCTION The enhancement in electrical conductivity of insulating polymers, by mixing them with specific conduc- tive tillers, such as metallic particleslpowderifibers, carbon black, ionic conductive polymers, and intrinsically conduc- tive polymeric powders has found applications ranging from EM1 (Electromagnetic 1nterference)RFI (Radio Fre- quency Interference) shielding in computer and cellular phone housings, to automobile tires to chemical and pbysi- cal sensing 111. Polymer-carbon composites used as sensing media in the Electronic Nose (ENose) built at JPL [2-71 will be the focus of this work. An electronic nose is an array of chemical sensors, which respond when exposed to vapors. The response of the sensor to an analyte is determined by he relative change in resistance AR& (vide infra). Each iensor is non-specific to any one vapor. Upon exposure to L vapor, the sensors respond with a conductivity change, xeating a pattem across the array. The pattem of distrib- ited response may be deconvoluted, and the contaminants dentified and quantified using a software analysis program ;uch as pattem recognition, neural network or principal mmponent analysis. There are however various extemal or
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This note was uploaded on 02/24/2011 for the course AERO 520 taught by Professor Rs during the Spring '11 term at Istanbul Technical University.

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ar6 - Temperature effects on polymer-carbon composite...

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