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Modification of visible light emission from silicon nanocrystals as a function of size, electronic structure, and surface passivation

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Materials Research Society Symposium - Proceedings 1999年 536卷 185-190页

作者： Wolkin, M.V. Jorne, J. Allan, G. Delerue, C. Materials Science Program Department of Chemical Engineering University of Rochester Rochester NY 14627 United States

The effect of surface passivation and crystallite size on the photoluminescence of porous silicon is reported. Oxygen-free porous silicon samples with medium to ultra high porosities have been prepared by using electrochemical etching followed by photoassisted stain etching. As long as the samples were hydrogen-passivated the PL could be tuned from the red (750nm) to the blue (400nm) by increasing the porosity. We show that when surface oxidation occurred, the photoluminescence was red-shifted. For sizes smaller than 2.8nm, the red shift can be as large as 1eV but for larger sizes no shift has been observed. Comparing the experimental results with theoretical calculations, we suggest that the decrease in PL energy upon exposure to oxygen is related to recombination involving an electron or an exciton trapped in Si=O double bonds. This result clarifies the recombination mechanisms in porous silicon.

关键词： Porous silicon

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Molecular design considerations in the synthesis of high conductivity PEMs for fuel cells

American Chemical Society, Polymer Preprints, Division of Po...

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American chemical Society, Polymer Preprints, Division of Polymer Chemistry 1999年第2期40卷 480-481页

作者： Zhang, Yue Litf, Morion Savinell, Robert F. Wainright, Jesse S. Department of Macromolecular Science Cleveland OH 44106 United States Department of Chemical Engineering Case Western Reserve Univeristy Cleveland OH 44106 United States

Highly conductive solid polymer electrolytes could be obtained using molecular design concepts to guide the work. The comonomers can regulate the polymer interchain spacing when one uses rigid rod, liquid crystal polymers. With larger interchain spacings, more free volume is available for water to occupy, and higher proton conductivity results.

关键词： Polyimides

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Ring-opening polymerization of ethylene carbonate and depolymerization of poly(ethylene oxide-co-ethylene carbonate)

American Chemical Society, Polymer Preprints, Division of Po...

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American chemical Society, Polymer Preprints, Division of Polymer Chemistry 1999年第2期40卷 772-773页

作者： Lee, Jong-Chan Litt, Morton H. School of Chemical Engineering Seoul National University Seoul 151-742 Korea Republic of Department of Macromolecular Science Case Westen Reserve University Cleveland OH 44106 United States

The ring-opening polymerization of ethylene carbonate (EC) is studied, along with the depolymerization of the resulting polyethylene oxide-co-ethylene carbonate. Polymers containing EC and ethylene oxide backbone repeats are formed as long as the monomers are present, once all the monomers are consumed, the polymers started to cleave. Hydrolysis results and polymer composition data show that two consecutive ethylene oxide units and one ethylene carbonate unit are the major backbone repeats in the early stage of polymerization. These repeats can be formed by the combination of one alkylene carbon attack and two carbonyl carbon attack by the active chain ends.

关键词： Copolymers

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Integrating research into the undergraduate curriculum - NASA's microgravity bioreactor

Integrating research into the undergraduate curriculum - NAS...

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1999 ASEE Annual Conference and Exposition: engineering Education to Serve the World

作者： Francis, Shani Schimmel, Keith Pellis, Neal R. North Carolina A and T State Univ. Johnson Space Center Chemical Engineering Department North Carolina A and T State Univ. Greensboro NC Biotechnology Cell Science Program Natl. Aero. and Space Administration Johnson Space Center Houston TX

Currently, there is an emphasis in many funding agencies on integrating research results into the undergraduate curriculum. The basic rationale is that research expenditures will thus be leveraged to improve the quality of undergraduate education by providing students with interesting, real world engineering problems that will motivate, provide opportunities for students to integrate material from different courses, and develop problem solving skills. While there is little disagreement as to the potential benefits of this approach, there is the need for models of how to efficiently perform the research-teaching integration. This paper explores the use of Macromedia Authorware 5 Attain ® to develop an interactive multimedia module that will test the research integration concept and its feasibility. The module explores the NASA microgravity bioreactor, which was developed in the late 1980's and is significantly impacting the tissue culture research community. The module is structured to interactively lead students through a problem solving strategy that involves problem definition, solution generation, decision analysis, solution implementation, and solution evaluation. Topics covered in the module will include ones that are typically covered in introductory numerical methods and data analysis courses. Initial testing of the module is in a sophomore level introduction to chemical engineering analysis and design course.

关键词： engineering education

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In-situ characterization of surface molecular orientation of polymer films by fiber optic UV reflection dichroism

American Chemical Society, Polymer Preprints, Division of Po...

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American chemical Society, Polymer Preprints, Division of Polymer Chemistry 1999年第2期40卷 673-674页

作者： Weir, Michael D. Sung, Chong Sook Paik Sung, Nak Ho Polymer Program Institute of Materials Science University of Connecticut Storrs CT 06269-3136 United States Department of Chemical Engineering Tufts University Medford MA 02155 United States

The surface molecular orientation of polyethylene terephthalate (PET) films is measured using a bifurcated fiber-optic probe. The use of bifurcated fiber-optic probe in the measurement of UV dichroism using reflection techniques is successful when the polarizer is placed at the probe end, which minimizes the depolarization effect of birefringence due to external factors acting upon the fiber. This is seen by the close agreement of the dichroic ratio and orientation function when using either the specular reflection accessory or the bifurcated fiber optic. While the magnitude of reflection may change using different methods, then overall orientation measured stays relatively constant.

关键词： Plastic films

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Uniform National Discharge Standards - Overview and implications for future naval engineering

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NAVAL ENGINEERS JOURNAL 1999年第3期111卷 219-235页

作者： Kopack, D Smith, G Kim, D Erne, DL David F. Kopack:is a Program Manager in the Naval Sea Systems Command Office of Environmenta1 Protection Occupational Safety and Health SEA 00T. Mr. Kopack received his bachelor and master of science degrees in the physical sciences and management from the University of Maryland. Mr. Kopack has 20 years of experience in ship design and engineering industrial facility operations and program management. Gordon D. Smith:is a Chemical Engineer with the Carderock Division Naval Surface Warfare Center in Bethesda Maryland and is working in the Naval Sea Systems Command Environmental and Auxiliary Systems Group. SEA 03L. Mr. Smith received his bachelor of science degree in chemical engineering from The Ohio State University. He has over 13 years of ronmental issues. In addition to supporting the development of Uniform National Discharge Standards he has been involved in research design testing and development of pollution abatement technologies suitable for use aboard Navy Ships. Don K. Kim:is a Senior Mechanical Engineer with the naval architecture and marine engineering firm of M. Rosenblatt & Son Inc. in Arlington Virginia. Mr. Kim received his bachelor of science and master of engineering degrees in mechanical engineering from the University of Virginia. He is a registered Professional Engineer in the Commonwealth of Virgina. Mr. Kim has ten years of experience in the design installation maintenance and repair of shipboard mechanical systems equipment and components with specific expertise in compressor pump and fan design and operation. He is a member of the American Society of Naval Engineers and the American Society of Mechanical Engineer. David L. Erne:is an Associate with Booz Allen and Hamilton Inc. in Arlington Virginia. Mr. Erne received his bachelor of science degree in chemical engineering from the University of Idaho. He has over twelve years of experience in environmental program management and consulting. In addition to his support for the Uniform National Discharge Standards prog

In the Fiscal Year 1996 National Defense Authorization Act, Congress amended the Clean Water Act to provide the department of Defense and the Environmental Protection Agency authority to jointly establish standards for incidental discharges from Armed Forces' vessels. The uniform national standards would apply to discharges from vessels of the Navy, Military Sealift Command, Army, Marine Corps, Air Force, and Coast Guard to the navigable waters and contiguous zone of the U.S. and its territories. Uniform National Discharge Standards (UNDS) will require control of discharges, by either a technology or management practice. UNDS will facilitate the Armed Forces' ability to better design and build future vessels to be environmentally sound and to maintain the operational flexibility of Armed Forces' vessels both domestically and internationally. The development of standards for Armed Forces' vessel discharges may have greater impact on naval engineering requirements for future vessels than any other single environmental issue, These standards are expected to stimulate the development of innovative vessel pollution control technologies, which on be used for both Armed Forces' vessels and commercial shipping vessels. This paper provides an overview of UNDS development, summarizes the results of UNDS Phase I, provides a summary overview of the preliminary approach for accomplishing UNDS Phase Il, and discusses implications for future naval engineering efforts.

关键词： Replenishment at sea homeland defense shipbuilding Military Personnel Uniform home range Treated water Naval engineering Uniforms Implication Clean Water Act Coastguards

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Blackwater and Graywater on US navy ships: Technical challenges and solutions

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NAVAL ENGINEERS JOURNAL 1999年第3期111卷 293-306页

作者： Benson, J Caplan, I Jacobs, R John Benson:received his BS degree in Mechanical Engineering and MS degree in Environmental Engineering from the University of Maryland. He is a registered Professional Engineer in the State of Maryland. He Joined the Naval Sufrace Warfare Center Carderock Division Environmental Quality Department in 1990 as a project engineer and is now managing the non-oily wastewater (graywater and blackwater) project area. Mr. Ivan Caplan:graduated from Drexel University (Philadelphia Pennsylvania) with a BS in Metallurgical Engineering and was awarded a MS degree from the Johns Hopkins University (Baltimore Maryland) in Mechanics and Materials Science. Mr. Caplan has spent most of his career at the Carderock Division Naval Surface Warfare Center (NSWC) and is currently the Head of the Wastewater Management Branch in the Carderock Division's Environmental Quality Department. Previously Mr. Caplan managed the US Navy's Applied Research Program in Ship & Submarine Materials Technology. In addition Mr. Caplan was manager of the US Navy's Titanium Technology Program Office and during his government career held several external Program Manager positions on at the Naval Sea Systems Command and another at the Air Force Office of Scientific Research. Rachel Jacobs:received BS degrees in Chemical Engineering and Marine Biology from the University of Maryland College Park. After working for the Naval Research Laboratory in Washington DC and the Center for Marine Biotechnology in Baltimore MD she joined the staff of the Naval Surface Warfare Center's Environmental Quality Department in 1997. Since thta time Ms. Jacobs has worked in the non-oily wastewater treatment area and her principal responsibility has been to technically supervise the evaluation operation and modification graywater treatment.

In anticipation of more stringent environmental regulations, the increasing costs of waste disposal, and the need for naval combatants to operate unimpeded in littoral waters, the U.S. Navy has identified the need to develop technologies which are appropriate for the control and treatment of blackwater and graywater. This paper will describe the status of development efforts by the Carderock Division, Naval Surface Warfare Center (CDNSWC) and its supporting contractors, under sponsorship of Naval Sea Systems Command (NAVSEA) and the Office of Naval Research. The challenge was to develop treatment systems that meet Navy shipboard requirements for affordability, compactness, low manning/maintenance, high reliability and safety, and EM, noise, vibration and shock. Membrane ultrafiltration based systems, incorporating aerobic biological pre-treatment and ultraviolet light post treatment disinfection, have ken developed to meet these requirements. Both external and in-tank membrane systems will be described in terms of performance, system operation and space and weight advantages.

关键词： Naval vessels

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Small-angle X-ray scattering studies of zinc stearate-filled sulfonated poly(ethylene-co-propylene-co-ethylidene norbornene) ionomers

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Journal of Polymer science 1999年第21期37卷

作者： D. A. Jackson J. T. Koberstein R. A. Weiss Polymer Science Program Department of Chemical Engineering University of Connecticut Storrs Connecticut 06269-3136

The crystallization, melting, and dissolution behavior of zinc stearate (ZnSt) in ZnSt-filled sulfonated poly(ethylene-co-propylene-co-ethylidene norbornene) (SEPDM) ionomers was studied by synchrotron small-angle X-ray scattering (SAXS). The melting temperature of ZnSt in the ionomer was considerably lower than in the pure state, which was consistent with the existence of very small ZnSt crystalline domains and a specific interaction between the metal sulfonate groups of the SEPDM and the metal carboxylate groups of ZnSt. Temperature-resolved SAXS showed that, on melting, some or all of the ZnSt rapidly dissolved into the ionomer. Ionic aggregates in the neat ionomer persisted up to 300°C. Microphase separation was also observed at elevated temperatures for the ZnSt-filled ionomers, but the composition of the microdomains was believed to be quite different than that of the microdomains in the neat SEPDM. The time and temperature dependence of the ZnSt crystallization in the filled ionomers was characterized by time-resolved SAXS experiments following a temperature quench from the melt. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3141–3150, 1999

关键词： ionomer X-ray scattering sulfonated EPDM stearate introduction

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In vitrocytotoxicity andin vivobiocompatibility of poly(propylene fumarate-co-ethylene glycol) hydrogels

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Journal of Biomedical Materials Research Part B: Applied Biomaterials 1999年第1期46卷

作者： Laura J. Suggs Matthew S. Shive C. Alejandra Garcia James M. Anderson Antonios G. Mikos Cox Laboratory for Biomedical Engineering Institute of Biosciences and Bioengineering and Department of Chemical Engineering Rice University 6100 South Main Street Houston Texas 77251-1892 Departments of Pathology Biomedical Engineering and Macromolecular Science Case Western Reserve University Cleveland Ohio 44106

The in vitro cytotoxicity and in vivo biocompatibility of poly(propylene fumarate- co -ethylene glycol) [P(PF- co -EG)] hydrogels were assessed in order to investigate the influence of poly(ethylene glycol) molecular weight and copolymer composition. These materials have application as injectable cardiovascular implants; cytotoxicity due to leachable products, as well as inflammation caused by the biomaterial itself, may ultimately affect the biocompatibility of the implant. We utilized a 7-day in vitro cytotoxicity assay to quantify cell density and cellular proliferation in the presence of copolymer films. The copolymer films exhibited slight to moderate cytotoxicity toward cultured endothelial cells, showing 20–86% viability relative to controls. Cell viability increased with an increasing weight percent of PEG or, to a lesser extent, the molecular weight of PEG. In vivo biocompatibility was assessed using a cage implantation model over a 21-day time period. This system was used to characterize the local cellular and humoral inflammatory response in the surrounding exudate, as well as the size and density of macrophages adherent to the material itself. All copolymer formulations exhibited excellent biocompatibility relative to controls with no significant differences in total leukocyte count among the different formulations. The in vivo inflammatory reaction displayed normal wound healing over 21 days as shown by a progressive decrease in both leukocyte concentration and enzymatic activity. The surface coverage of the copolymer films remained relatively constant from 7 to 21 days. There were no cells larger than 0.003 mm 2 , which was previously shown to be the threshold value for foreign-body giant cells. These data suggest that P(PF- co -EG) hydrogels have potential for use as injectable biomaterials.© 1999 John Wiley & Sons, Inc. J Biomed Mater Res, 46, 22–32, 1999.

关键词： cytotoxicity biocompatibility hydrogel poly(ethylene glycol) poly(propylene fumarate) cardiovascular stent tissue engineering

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Polybenzoxazine resins: Aspects of interaction and adsorption behavior

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Journal of Polymer science 1999年第13期37卷

作者： Ruijian Xu Henry P. Schreiber Mitchell Huang Hatsuo Ishida CRASP Department of Chemical Engineering Ecole Polytechnique Montreal Quebec H3C 3A7 Canada NSF Center for Molecular and Microstructure of Composites Department of Macromolecular Science Case Western Reserve University Cleveland Ohio 44106

The technique of inverse gas chromatography (IGC) has been used to evaluate the acid–base interaction potential of two polybenzoxazines. One of these, prepared from bisphenol-A monomer, was shown to be a net base. Another based on dihydroxybenzophenone registered as a net acid. The bisphenol-A version was adsorbed at controlled thicknesses on α-alumina, on fumed silica and on boron nitride, all three solids with acidic surfaces as shown by IGC data. Thin layers of the adsorbed polymer near monolayer coverage were strongly perturbed by the underlying substrate, the polymer surface now behaving as a net acid. Thicker layers of the adsorbed polymer revert to basicity, but fail to attain the acid–base interaction constants of the pure polymer. The presence of strongly interactive substrates leads to the creation of a substantial interphase, the interaction properties of the adsorbed polymer varying through the thickness of this layer. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1441–1447, 1999

关键词： polybenzoazines inverse gas chromatography adsorption acid–base characteristics

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