Adam Kisor

Correlating Polymer-Carbon Composite Sensor Response with Molecular Descriptors

We report a quantitative structure-activity relationships QSAR study using genetic function approximations to describe the activities of a polymer-carbon composite chemical vapor sensor using a novel approach to selecting a molecular descriptor set. The measured sensor responses are conductivity changes in polymer-carbon composite films upon exposure to target vapors at partsper-million concentrations. The descriptor set combines the basic analyte descriptor set commonly used in QSAR studies with descriptors for sensing film-analyte interactions. The basic analyte descriptors are obtained using a combination of empirical and semiempirical quantitative structure-property relationships methods. The descriptors for the sensing film-analyte interactions are calculated using molecular modeling and simulation tools. A statistically validated QSAR model was developed for a training data set consisting of 17 analyte molecules. The applicability of this model was also tested by predicting sensor activities for three test analytes not considered in the training set.

Expanding the capabilities of the JPL electronic nose for an International Space Station technology demonstration

An array-based sensing system based on polymer/carbon composite conductometric sensors is under development at JPL for use as an environmental monitor in the International Space Station. Sulfur dioxide has been added to the analyte set for this phase of development. Using molecular modeling techniques, the interaction energy between SO2 and polymer functional groups has been calculated, and polymers selected as potential SO2 sensors. Experiment has validated the model and two selected polymers have been shown to be promising materials for SO2 detection.

Development of the Third Generation JPL Electronic Nose for International Space Station Technology Demonstration

The capabilities of the JPL Electronic Nose have been expanded to include characteristics required for a Technology Demonstration schedule on the International Space Station (ISS) in 2008-2009 [1,2]. Concurrently, to accommodate specific needs on ISS, the processes, tools and analyses which influence all aspects of development of the device have also been expanded. The Third Generation ENose developed for this program uses two types of sensor substrates, newly developed inorganic and organic sensor materials, redesigned electronics, onboard near real-time data analysis and power and data interfaces specifically for ISS. This paper will discuss the Third Generation ENose with a focus on detection of mercury in the parts-per-billion range.

Expanding the Analyte Set of the JPL Electronic Nose to Include Inorganic Species

An array-based sensing system based on 32 polymer/carbon composite conductometric sensors is under development at JPL. Until the present phase of development, the analyte set has focused on organic compounds (common solvents) and a few selected inorganic compounds, notably ammonia and hydrazine. The present phase of JPL ENose development has added two inorganics to the analyte set: mercury and sulfur dioxide. Through models of sensor-analyte response developed under this program coupled with a literature survey, approaches to including these analytes in the ENose target set have been determined.

The JPL electronic nose: Monitoring air in the U.S. Lab on the International Space Station

An electronic nose with a sensor array of 32 conductometric sensors has been developed at the Jet Propulsion Laboratory (JPL) to monitor breathing air in spacecraft habitat. The Third Generation ENose is designed to operate in the environment of the U.S. Lab on the International Space Station (ISS). It detects a selected group of analytes at target concentrations in the ppm regime at an environmental temperature range of 18 – 30 °C, relative humidity from 20 – 75% and pressure from 530 to 760 torr. The monitoring targets are anomalous events such as leaks and spills of solvents, coolants or other fluids. The JPL ENose operated as a technology demonstration for seven months in the U.S. Laboratory Destiny during 2008–2009. Analysis of ENose monitoring data shows that there was regular, periodic rise and fall of humidity and occasional releases of Freon 218 (perfluoropropane), formaldehyde, methanol and ethanol. There were also several events of unknown origin, half of them from the same source. Each event lasted from 20 to 100 minutes, consistent with the air replacement time in the U.S. Lab.

Ground Validation of the Third Generation JPL Electronic Nose

The Third Generation ENose is an air quality monitor designed to operate in the environment of the US Lab on the International Space Station. It detects a selected group of analytes at target concentrations in the ppm regime at an environmental temperature range of 18 30 o C, relative humidity from 25 - 75% and pressure from 530 to 760 torr. The abilities of the device to detect ten analytes, to reject confounders as “unknown” and to deconvolute mixtures of two analytes under varying environmental conditions has been tested extensively in the laboratory. Results of ground testing showed an overall success rate for detection, identification and quantification of analytes of 87% under nominal temperature and humidity conditions and 83% over all conditions.

Operation of Third Generation JPL Electronic Nose on the International Space Station

The Third Generation ENose is an air quality monitor designed to operate in the environment of the US Lab on the International Space Station (ISS). It detects a selected group of analytes at target concentrations in the ppm regime at an environmental temperature range of 18 - 30 o C, relative humidity from 25 - 75% and pressure from 530 to 760 torr. This device was installed and activated on ISS on Dec. 9, 2008 and has been operating continuously since activation. Data are downlinked and analyzed weekly. Results of analysis of ENose monitoring data show the short term presence of low concentration of alcohols, octafluoropropane and formaldehyde as well as frequent short term unknown events.

Temperature effects on polymer-carbon composite sensors: Evaluating the role of polymer molecular weight and carbon loading

We report the effect of temperature coupled with varying polymer molecular weight and carbon loadings on the performance of polymer-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 connectivity and tunneling, it is not fully understood how environmental conditions and intrinsic polymer and filler properties affect polymer composite sensor characteristics and responses. Composites of polyethylene oxide (PEO)-carbon black (CB) considered here include PEO polymers with molecular weights of 20K, 600 K and 1M. The effects of polymer molecular weight on the percolation threshold of PEO-carbon composite and incremental sensor temperature effects on PEO-carbon sensor response were investigated. 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 different carbon loadings; these changes may be explained by a change in conduction mechanism.

Advances in electrode materials for AMTEC

A mixed conducting electrode for the Alkali Metal Thermal to Electric Converter (AMTEC) has been made and tested. The electrode is made from a slurry of metal and TiO2 powders which is applied to the electrolyte and fired to sinter the electrode material. During the first 48–72 hours of operation in a SETC, the electrode takes up Na from low pressure sodium vapor to make a metal-Na-Ti-O compound. This compound is electronically conducting and ionically conducting to sodium; electronic conduction is also provided by the metal in the electrode. With a mixed conducting electrode made from robust, low vapor pressure materials, the promise for improved performance and lifetime is high.

Polymer-based carbon monoxide sensors

Polymer-based sensors have been used primarily to detect volatile organics and inorganics; they are not usually used for smaller, gas phase molecules. We report the development and use of two types of polymer-based sensors for the detection of carbon monoxide. Further understanding of the experimental results is also obtained by performing molecular modeling studies to investigate the polymer-carbon monoxide interactions. The first type is a carbon-black-polymer composite that is comprised of a non-conducting polymer base that has been impregnated with carbon black to make it conducting. These chemiresistor sensors show good response to carbon monoxide but do not have a long lifetime. The second type of sensor has a non-conducting polymer base but includes both a porphyrin-functionalized polypyrrole and carbon black. These sensors show good, repeatable and reversible response to carbon monoxide at room temperature.