We report here the chemical modification of poly(methyl methacrylate) (PMMA) surfaces by their reaction with the monoanion of alpha,omega-diaminoalkanes (aminolysis reaction) to yield amine-terminated PMMA surfaces. It is found that the amine functionalities are tethered to the PMMA backbone through an alkane bridge to amide bonds formed during the aminolysis of the surface ester functionalities. The distribution of the amine termini is quite uniform as judged by fluorescence micrographs. It is found that the electroosmotic flow in aminated PMMA microchannels is reversed when compared to that in unmodified channels. In addition, it is demonstrated that enzymes can be immobilized onto the amine-terminated PMMA surfaces and are effective in the restriction digestion of dsDNAs. Finally, the availability of the surface amine groups is further demonstrated by their reaction with n-octadecane-1-isocyanate to form PMMA surfaces terminated with well-ordered and highly crystalline octadecane chains.
Polymer electrolyte membrane (PEM) fuel cells use components that are susceptible to contaminants in the fuel stream. To ensure fuel quality, standards are being set to regulate the amount of impurities allowable in fuel. The present study investigates the effect of chlorinated impurities on fuel cell systems using tetrachloroethylene (PCE) as a model compound for cleaning and degreasing agents. Concentrations between 0.05 parts per million (ppm) and 30 ppm were studied. We show how PCE causes rapid drop in cell performances for all concentrations including 0.05 ppm. At concentrations of 1 and 0.05 ppm, PCE poisoned the cell at a rate dependent on the dosage of the contaminant delivered to the cell. PCE appears to affect the cell when the cell potential was over potentials higher than approximately 0.2 V. No effects were observed at voltages around or below 0.2 V and the cells could be recovered from previous poisoning performed at higher potentials. Recoveries at those low voltages could be induced by changing the operating voltage or by purging the system. Poisoning did not appear to affect the membrane conductivity. Measurements with long-path length IR results suggested catalytic decomposition of the PCE by hydrogen over the anode catalyst.Hydrogen used in low temperature fuel cell systems must contain low levels of impurities to minimize performance degradation that can shorten their lifetime. Setting hydrogen fuel standards as a part of the foundation for a hydrogen economy requires balancing fuel cell system degradation with the costs for hydrogen purification and certification. Since hydrogen fuel quality would be enforced at the connection nozzle between the fueling station and the vehicle, station owners must ensure that procedures to alter the station do not introduce contaminants into the fuel. There has been a large focus on the effects of carbon monoxide 1-7 and ammonia 8-14 on polymer electrolyte membrane fuel cells (PEMFC), however little information is available on the effect of less common contaminants such as chlorinated compounds. Halocarbons are proposed to be regulated as part of the International Organization for Standardization (ISO) and the Society of Automotive Engineers (SAE) fuel quality standards. The proposed limit for chlorinated compounds in both the ISO and SAE standards is 0.05 ppm of total chlorinated species. 15,16 It is not anticipated that chlorinated compounds will be found in hydrogen produced from natural gas and purified using liquefaction or a pressure swing absorption system, but chlorinated compounds could enter the fuel in cases where a hydrogen station is serviced or during cases of severe component malfunction.Chlorinated compounds have been investigated in fuel cell systems when looking at the operation of fuel cell systems in situations such as a battlefield environment, 17 however these contaminants are significantly different than the automotive environments served by ISO and SAE standards. The effect of chloride ions on fuel cell has been considered when lookin...
This report describes laboratory development and process plant applications of Raman spectroscopy for detection of hydrogen isotopes in the Tritium Facilities at the Savannah River Site (SRS), a U.S. Department of Energy complex. Raman spectroscopy provides a lower-cost, in situ alternative to mass spectrometry techniques currently employed at SRS. Using conventional Raman and fiber optics, we have measured, in the production facility glove boxes, process mixtures of protium and deuterium at various compositions and total pressures ranging from 1000 -4000 torr, with detection limits ranging from 1-2% for as low as 3-second integration times. We are currently investigating fabrication techniques for SERS surfaces in order to measure trace (0.01-0.1%) amounts of one isotope in the presence of the other. These efforts have concentrated on surfaces containing palladium, which promotes hydrogen dissociation and forms metal hydride bonds, essentially providing a chemical enhancement mechanism.
EXECUTIVE SUMMARYThe problem of the aging mass spectrometers coupled with lack of vendor support and no viable commercially available replacement presents risks for process control and monitoring in the Tritium Facilities. Therefore, several technologies were evaluated to maintain and, if possible, to enhance the current analytical capabilities provided by the existing mass spectrometers. These technologies included potential replacement/complement mass spectrometers as well as on-line sensors. Based on the results of this evaluation, the Savannah River National Laboratory (SRNL) makes the following recommendations.• Work should begin on implementation of the Quantra Fourier Transform-Ion CyclotronResonance (FT-ICR) as a complement to the existing mass spectrometers or as an on-line process analyzer. In its current configuration, the instrument can measure masses 12 or greater, with a resolution of 30,000 at mass 28, and 100 part per million detection limit using ion ejection of major ions. Thus, the 16-24 mass region that is not so easily separated by the existing Tritium Facility mass spectrometers could be resolved and measured using the FT-ICR. For the FT-ICR (Quantra) to be of even more benefit to the Tritium Facilities, it should be reengineered to provide analysis of masses 2-1000 in a single scan as well as other hardware and software improvements identified during our evaluation (i.e. long term stability, quantitative analysis of mixtures, etc.). In collaboration, SRS, LANL, and Y12 have secured funding for this project and the re-engineering effort will begin in FY06. Once the re-engineering effort is complete, funding will be required for performance testing and implementation in a tritiated environment as well as validation with the design agency.• The bench top magnetic sector mass spectrometer (GCMATE) technology closely matches that of the existing mass spectrometers in the Tritium Facilities. The initial work with the GCMATE indicates that its resolution and sensitivity meet the requirements of a replacement mass spectrometer for the Tritium Facilities. Although this instrument appears to be the most promising as a replacement for the existing mass spectrometers, delayed funding in FY05 precluded a complete evaluation. Therefore, evaluation of this instrument should continue in FY06.• Fiber optic Raman Spectroscopy has been demonstrated as a useful on-line technology for measurement of hydrogen isotopes at a concentration of greater than 1%. The method should be demonstrated on a process containing tritium. Upon successful demonstration in a tritium process, the method should then be implemented on the Hydrogen-Tritium Thermal Cycling Adsorption Process (HT-TCAP) and other processes that would require a detection limit of 1% or greater. Research and development to improve the detection limit of the fiber optic Raman method should continue as this would allow on-line analysis of other process points (i.e. HT-TCAP product and raffinate, Tritium Process Stripper, etc.).• The on-line vapochromic sens...
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