Grantee Research Project Results
1999 Progress Report: Development of a Miniature Detector for Accurate Identification of Toxic Environmental Contaminants (DATEC)
EPA Grant Number: R826648Title: Development of a Miniature Detector for Accurate Identification of Toxic Environmental Contaminants (DATEC)
Investigators: Tepper, Gary C.
Institution: Virginia Commonwealth University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $302,268
RFA: Exploratory Research - Environmental Chemistry (1998) RFA Text | Recipients Lists
Research Category: Air , Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities
Objective:
The objective of the project is the development of a new chemical sensor technology that will allow accurate in situ identification and quantification of volatile organic compounds (VOCs) in the environment. Specifically, the detector will be small, portable, inexpensive, and capable of monitoring the presence of a wide range of atmospheric contaminants.Progress Summary:
A literature search was performed to identify and select the most appropriate polymers for the DATEC sensor. Chemical selectivity, thermal stability, amenable solubility, and appropriate VOC interaction energy were the primary metrics against which each candidate was compared. A detailed matrix cross-listing the most promising commercially available polymers and associated properties was generated and includes the family of polysiloxanes and polyisobutylene.
The design and testing of the new Rapid Expansion of Supercritical Solutions (RESS) polymer-coating apparatus was completed, and the system now is fully operational. The system includes the unique ability to control not only temperature and pressure, but the concentration of the supercritical solution, which is accomplished by incorporating a special high-pressure reactor with a floating piston, allowing for much greater control over the polymer coating properties. The new design also includes a separate high pressure phase monitor for performing polymer solubility measurements in supercritical solutions.
Polyisobutylene and polysiloxane coatings were deposited using RESS and characterized using optical and scanning electron microscopy. The coating morphology could be controlled by adjusting the RESS expansion parameters, and ranged from uniform films to micro- or nanometer-sized particles with narrow size distributions.
Two additional methods for coating the surface acoustic wave (SAW) transducer were tested: solvent casting and self-assembled monolayers (SAMs). The solvent casting technique was eliminated because it did not allow sufficient control over coating thickness. The SAM method showed promising results for certain polymers. Several surface cleaning methods also were tested.
The design and construction of the coating analysis environmental chamber was completed. The purpose of the chamber is to quantify and calibrate the sensor performance parameters, including the thermal desorption signature of specific VOCs, sensor sensitivity, and response time. The chamber includes a quadrupole mass spectrometer, a surface heater, a high tolerance bleed-in valve, and various temperature and pressure transducers. The chamber pressure can be controlled from ultra high vacuum (10-10 Torr) to atmospheric conditions, and VOC concentrations can be controlled to the parts per trillion level.
Characterization and comparison of the thermal stability of SAW and surface plasm on resonance (SPR) transducers were completed. The differential SAW frequency was monitored under thermal variations of up to 50oC. It was determined that, by providing very uniform heating, the SAW stability could be maintained to less than 10 Hz/o C. For comparison, the thermal stability of an SPR sensor was tested and found to provide even greater thermal stability. It is, therefore, under consideration as an alternative transducer for the DATEC sensor.
SAW transducers coated with polyisobutylene nanoparticles were exposed to hexane vapor at atmospheric conditions. The transducers demonstrated excellent sensitivity and reversible response. Additional testing is underway to characterize the sensor selectivity to various vapors and to investigate the relationship between coating morphology and sensor response.
Future Activities:
All project tasks are proceeding on schedule. The next activities include: coating development using RESS, coating analysis using microscopy and infrared spectroscopy, and detector characterization in the environmental chamber.Journal Articles:
No journal articles submitted with this report: View all 24 publications for this projectSupplemental Keywords:
VOC sensor, atmospheric contaminants, air pollution, VOCs, portable sensor, environmental monitoring., Air, Scientific Discipline, Toxics, Engineering, Chemistry, Environmental Chemistry, Engineering, Chemistry, & Physics, VOCs, Environmental Monitoring, toxic contaminants, air sampling, DATEC, field portable systems, thermally stable polymer film, chemical composition, spectroscopy, chemical detection techniques, field monitoring, analytical chemistry, spectroscopic studies, portable atmospheric contamination detectorProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.