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Full-Text Articles in Engineering
Addressing Our Global Water Future, Center For Strategic And International Studies (Csis), Sandia National Laboratories
Addressing Our Global Water Future, Center For Strategic And International Studies (Csis), Sandia National Laboratories
US Department of Energy Publications
This White Paper addresses the growing global challenges of dealing with the devastating effects of increasing water scarcity and declining water quality. Across the planet, in developing and developed regions alike, poor governance and mismanagement of natural resources coupled with rising population growth, increasing urbanization, and economic development have led to a growing imbalance between water supply and demand. This imbalance is reaching crisis proportions in many regions. It will have even more significant consequences for economic development, stability and security unless the there is a more dramatic and urgent international response. Several international forums have arisen to address just …
Uranium Geochemistry In Vadose Zone And Aquifer Sediments From The 300 Area Uranium Plume, John M. Zachara, J. A. Davis, James Mckinley, D. M. Wellman, Chongxuan Liu, N. Qafoku, S. B. Yabusaki
Uranium Geochemistry In Vadose Zone And Aquifer Sediments From The 300 Area Uranium Plume, John M. Zachara, J. A. Davis, James Mckinley, D. M. Wellman, Chongxuan Liu, N. Qafoku, S. B. Yabusaki
US Department of Energy Publications
In 1996, an interim record of decision was issued for the 300-FF-5 Operable Unit on the Hanford Site in southeast Washington State. The record of decision specified the interim remedy as (1) continued monitoring of groundwater and (2) institutional controls to restrict groundwater use. This record of decision was based on a remedial investigation that suggested levels of uranium would decrease with time because of natural geochemical and hydrologic processes. A prediction was made that concentrations of uranium would decrease to the proposed drinking water standard or lower (20 μg/L) in 3 to 10 years from 1993. This prediction has …
Ferrous Hydroxy Carbonate Is A Stable Transformation Product Of Biogenic Magnetite, Ravi K. Kukkadapu, John M. Zachara, James K. Fredrickson, David W. Kennedy, Alice C. Dohnalkova, David E. Mccready
Ferrous Hydroxy Carbonate Is A Stable Transformation Product Of Biogenic Magnetite, Ravi K. Kukkadapu, John M. Zachara, James K. Fredrickson, David W. Kennedy, Alice C. Dohnalkova, David E. Mccready
US Department of Energy Publications
An ~1:1 mixture of ferrihydrite and nanocrystalline akaganeite (β-FeOOH; 10–15 nm) was incubated with Shewanella putrefaciens (strain CN32) under anoxic conditions with lactate as an electron donor and anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. The incubation was carried out in a 1,4-piperazinediethanesulfonic acid (PIPES)-buffered medium, without PO34– at circumneutral pH. Iron reduction was measured as a function of time (as determined by 0.5 N HCl extraction), and solids were characterized by X-ray diffraction (XRD), electron microscopy, and Mössbauer spectroscopy. The biogenic reduction of Fe3+was rapid; with 60% of the total Fe (FeTOT) reduced …
Chemical Mapping Of Polymer Photoresists By Scanning Transmission X-Ray Microscopy, Ligia Muntean, Romain Planques, A. L. D. Kilcoyne, Stephen R. Leone, Mary Gilles, William D. Hinsberg
Chemical Mapping Of Polymer Photoresists By Scanning Transmission X-Ray Microscopy, Ligia Muntean, Romain Planques, A. L. D. Kilcoyne, Stephen R. Leone, Mary Gilles, William D. Hinsberg
US Department of Energy Publications
Scanning transmission x-ray microscopy (STXM) is shown to be a powerful imaging technique that provides chemical selectivity and high spatial resolution (~35 nm) for studying chemically amplified photoresists. Samples of poly (4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a line/space pattern of 1.10 μm/ 0.87 μm followed by a post-exposure bake, are used to demonstrate STXM imaging capabilities to extract photoresist latent images. Chemical contrast is obtained by measuring the x-ray absorption at an energy of 290.5 eV, corresponding to a carbon K shell electronic transition to the unoccupied π* molecular orbital of the PTBOCST …
Effects Of Sediment Iron Mineral Composition On Microbially Mediated Changes In Divalent Metal Speciation: Importance Of Ferrihydrite, D. Craig Cooper, Andrew L. Neal, Ravi K. Kukkadapu, Dale Brewe, Aaron Coby, Flynn W. Picardal
Effects Of Sediment Iron Mineral Composition On Microbially Mediated Changes In Divalent Metal Speciation: Importance Of Ferrihydrite, D. Craig Cooper, Andrew L. Neal, Ravi K. Kukkadapu, Dale Brewe, Aaron Coby, Flynn W. Picardal
US Department of Energy Publications
Dissimilatory metal reducing bacteria (DMRB) can influence geochemical processes that affect the speciation and mobility of metallic contaminants within natural environments. Most investigations into the effect of DMRB on sediment geochemistry utilize various synthetic oxides as the FeIII source (e.g., ferrihydrite, goethite, hematite). These synthetic materials do not represent the mineralogical composition of natural systems, and do not account for the effect of sediment mineral composition on microbially mediated processes. Our experiments with a DMRB (Shewanella putrefaciens 200) and a divalent metal (ZnII) indicate that, while complexity in sediment mineral composition may not strongly impact the …
Control Of Fe(Iii) Site Occupancy On The Rate And Extent Of Microbial Reduction Of Fe(Iii) In Nontronite, Deb P. Jaisi, Ravi K. Kukkadapu, Dennis D. Eberl, Hailiang Dong
Control Of Fe(Iii) Site Occupancy On The Rate And Extent Of Microbial Reduction Of Fe(Iii) In Nontronite, Deb P. Jaisi, Ravi K. Kukkadapu, Dennis D. Eberl, Hailiang Dong
US Department of Energy Publications
A quantitative study was performed to understand how Fe(III) site occupancy controls Fe(III) bioreduction in nontronite by Shewanella putrefaciens CN32. NAu-1 and NAu-2 were nontronites and contained Fe(III) in different structural sites with 16 and 23% total iron (w/w), respectively, with almost all iron as Fe(III). Mössbauer spectroscopy showed that Fe(III) was present in the octahedral site in NAu-1 (with a small amount of goethite), but in both the tetrahedral and the octahedral sites in NAu-2. Mössbauer data further showed that the octahedral Fe(III) in NAu-2 existed in at least two environments- trans (M1) and cis (M2) sites. The microbial …
Development Of High-Temperature Ferromagnetism In Sno2 And Paramagnetism In Sno By Fe Doping, A. Punnoose, J. Hays, A. Thurber, M. H. Engelhard, Ravi K. Kukkadapu, C. Wang, V. Shutthanandan, S. Thevuthasan
Development Of High-Temperature Ferromagnetism In Sno2 And Paramagnetism In Sno By Fe Doping, A. Punnoose, J. Hays, A. Thurber, M. H. Engelhard, Ravi K. Kukkadapu, C. Wang, V. Shutthanandan, S. Thevuthasan
US Department of Energy Publications
We report the development of room-temperature ferromagnetism in chemically synthesized powder samples of Sn1−xFexO2 (0.005≤ x ≤0.05) and paramagnetic behavior in an identically synthesized set of Sn1−xFexO. The ferromagnetic Sn0.99Fe0.01O2 showed a Curie temperature TC=850 K, which is among the highest reported for transition-metal-doped semiconductor oxides. With increasing Fe doping, the lattice parameters of SnO2 decreased and the saturation magnetization increased, suggesting a strong structure-magnetic property relationship. When the Sn0.95Fe0.05O2 was prepared at different temperatures between …
Influence Of Calcite And Dissolved Calcium On Uranium(Vi) Sorption To A Hanford Subsurface Sediment, Wenming Dong, William Ball, Chongxuan Liu, Zheming Wang, Alan Stone, Jing Bai, John M. Zachara
Influence Of Calcite And Dissolved Calcium On Uranium(Vi) Sorption To A Hanford Subsurface Sediment, Wenming Dong, William Ball, Chongxuan Liu, Zheming Wang, Alan Stone, Jing Bai, John M. Zachara
US Department of Energy Publications
The influence of calcite and dissolved calcium on U(VI) adsorption was investigated using a calcite-containing sandy silt/clay sediment from the U. S. Department of Energy Hanford site. U(VI) adsorption to sediment, treated sediment, and sediment size fractions was studied in solutions that both had and had not been preequilibrated with calcite, at initial [U(VI)] ) 10-7-10-5 mol/L and final pH ) 6.0- 10.0. Kinetic and reversibility studies (pH 8.4) showed rapid sorption (30 min), with reasonable reversibility in the 3-day reaction time. Sorption from solutions equilibrated with calcite showed maximum U(VI) adsorption at pH 8.4 ± 0.1. …
Kinetic Desorption And Sorption Of U(Vi) During Reactive Transport In A Contaminated Hanford Sediment, Nikolla P. Qafoku, John M. Zachara, Chongxuan Liu, Paul Gassman, Odeta Qafoku, Steve Smith
Kinetic Desorption And Sorption Of U(Vi) During Reactive Transport In A Contaminated Hanford Sediment, Nikolla P. Qafoku, John M. Zachara, Chongxuan Liu, Paul Gassman, Odeta Qafoku, Steve Smith
US Department of Energy Publications
Column experiments were conducted to investigate U(VI) desorption and sorption kinetics in a sand-textured, U(VI)- contaminated (22.7 µmol kg-1) capillary fringe sediment from the U.S. Department of Energy (DOE) Hanford site. Saturated column experiments were performed under mildly alkaline conditions representative of the Hanford site where uranyl-carbonate and calcium-uranyl-carbonate complexes dominate aqueous speciation. A U(VI)-free solution was used to study contaminant U(VI) desorption in columns where different flow rates were applied. Sorbed, contaminant U(VI) was partially labile (11.8%), and extended leaching times and water volumes were required for complete desorption of the labile fraction. Uranium- (VI) sorption was …
Influence Of Sediment Bioreduction And Reoxidation On Uranium Sorption, Chongxuan Liu, John M. Zachara, Lirong Zhong, Ravi K. Kukkadapu, Jim Szecsody, Dave Kennedy
Influence Of Sediment Bioreduction And Reoxidation On Uranium Sorption, Chongxuan Liu, John M. Zachara, Lirong Zhong, Ravi K. Kukkadapu, Jim Szecsody, Dave Kennedy
US Department of Energy Publications
The influence of sediment bioreduction and reoxidation on U(VI) sorption was studied using Fe(III) oxide-containing saprolite from the U.S. Department of Energy (DOE) Oak Ridge site. Bioreduced sediments were generated by anoxic incubation with a metal-reducing bacterium, Shewanella putrefaciens strain CN32, supplied with lactate as an electron donor. The reduced sediments were subsequently reoxidized by air contact. U(VI) sorption was studied in Na- NO3-HCO3 electrolytes that were both closed and open to atmosphere and where pH, U(VI), and carbonate concentration were varied. Mössbauer spectroscopy and chemical analyses showed that 50% of the Fe(III)- oxides were reduced to …
Cryogenic Laser Induced U(Vi) Fluorescence Studies Of A U(Vi) Substituted Natural Calcite: Implications To U(Vi) Speciation In Contaminated Hanford Sediments, Zheming Wang, John M. Zachara, James Mckinley, Steven Smith
Cryogenic Laser Induced U(Vi) Fluorescence Studies Of A U(Vi) Substituted Natural Calcite: Implications To U(Vi) Speciation In Contaminated Hanford Sediments, Zheming Wang, John M. Zachara, James Mckinley, Steven Smith
US Department of Energy Publications
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) and imaging spectromicroscopy (TRLFISM) were used to examine the chemical speciation of uranyl in contaminated subsurface sediments from the U.S. Department of Energy (U.S. DOE) Hanford Site, Washington. Spectroscopic measurements for contaminant U(VI) were compared to those from a natural, uranyl-bearing calcite (NUC) that had been found via X-ray absorption spectroscopy (XAS) to include uranyl in the same coordination environment as calcium. Spectral deconvolution of TRLFS measurements on the NUC revealed the unexpected presence of two distinct chemical environments consistent with published spectra of U(VI)-substituted synthetic calcite and aragonite. Apparently, some U(VI) substitution sites in …
Fluorescence Spectroscopy Of U(Vi)-Silicates And U(Vi)-Contaminated Hanford Sediment, Zheming Wang, John M. Zachara, Paul Gassman, Chongxuan Liu, Odeta Qafoku, Wassana Yantasee, Jeff Catalano
Fluorescence Spectroscopy Of U(Vi)-Silicates And U(Vi)-Contaminated Hanford Sediment, Zheming Wang, John M. Zachara, Paul Gassman, Chongxuan Liu, Odeta Qafoku, Wassana Yantasee, Jeff Catalano
US Department of Energy Publications
Time-resolved U(VI) laser fluorescence spectra (TRLFS) were recorded for a series of natural uranium-silicate minerals including boltwoodite, uranophane, soddyite, kasolite, sklodowskite, cuprosklodowskite, haiweeite, and weeksite, a synthetic boltwoodite, and four U(VI)-contaminated Hanford vadose zone sediments. Lowering the sample temperature from RT to ~5.5 K significantly enhanced the fluorescence intensity and spectral resolution of both the minerals and sediments, offering improved possibilities for identifying uranyl species in environmental samples. At 5.5 K, all of the uranyl silicates showed unique, well-resolved fluorescence spectra. The symmetric O = U = O stretching frequency, as determined from the peak spacing of the vibronic bands …
Impact Of Highly Basic Solutions On Sorption Of Cs+ To Subsurface Sediments From The Hanford Site, Usa, C.C. Ainsworth, John M. Zachara, K. Wagnon, S. Mckinley, Chongxuan Liu, Steven Smith, H.T. Schaef, Paul Gassman
Impact Of Highly Basic Solutions On Sorption Of Cs+ To Subsurface Sediments From The Hanford Site, Usa, C.C. Ainsworth, John M. Zachara, K. Wagnon, S. Mckinley, Chongxuan Liu, Steven Smith, H.T. Schaef, Paul Gassman
US Department of Energy Publications
The effect of caustic NaNO3 solutions on the sorption of 137Cs to a Hanford site micaceous subsurface sediment was investigated as a function of base exposure time (up to 168 d), temperature (10°C or 50°C), and NaOH concentration (0.1 mol/L to 3 mol/L). At 10°C and 0.1 M NaOH, the slow evolution of [Al]aq was in stark contrast to the rapid increase and subsequent loss of [Al]aq observed at 50°C (regardless of base concentration). Exposure to 0.1 M NaOH at 10°C for up to 168 d exhibited little if any measurable effect on sediment mineralogy, Cs …
Oxidative Remobilization Of Biogenic Uranium(Iv) Precipitates: Effects Of Iron(Ii) And Ph, Lirong Zhong, Chongxuan Liu, John M. Zachara, David Kennedy, James E. Szecsody, Brian Wood
Oxidative Remobilization Of Biogenic Uranium(Iv) Precipitates: Effects Of Iron(Ii) And Ph, Lirong Zhong, Chongxuan Liu, John M. Zachara, David Kennedy, James E. Szecsody, Brian Wood
US Department of Energy Publications
The oxidative remobilization of uranium from biogenic U(IV) precipitates was investigated in bioreduced sediment suspensions in contact with atmospheric O2 with an emphasis on the influence of Fe(II) and pH on the rate and extent of U release from the solid to the aqueous phase. The sediment was collected from the U.S. Department of Energy Field Research Center (FRC) site at Oak Ridge, Tennessee. Biogenic U(IV) precipitates and bioreduced sediment were generated through anaerobic incubation with a dissimilatory metal reducing bacterium Shewanella putrefaciens strain CN32. The oxidative remobilization of freshly prepared and 1-yr aged biogenic U(IV) was conducted in 0.1 …
Enzymology Of Electron Transport: Energy Generation With Geochemical Consequences, Thomas J. Dichristina, James K. Fredrickson, John M. Zachara
Enzymology Of Electron Transport: Energy Generation With Geochemical Consequences, Thomas J. Dichristina, James K. Fredrickson, John M. Zachara
US Department of Energy Publications
Dissimilatory metal-reducing bacteria (DMRB) are important components of the microbial community residing in redox-stratified freshwater and marine environments. DMRB occupy a central position in the biogeochemical cycles of metals, metalloids and radionuclides, and serve as catalysts for a variety of other environmentally important processes including biomineralization, biocorrosion, bioremediation and mediators of ground water quality. DMRB are presented, however, with a unique physiological challenge: they are required to respire anaerobically on terminal electron acceptors which are either highly insoluble (e.g., Fe(III)- and Mn(IV)-oxides) and reduced to soluble end-products or highly soluble (e.g., U(VI) and Tc(VII)) and reduced to insoluble end-products. To …
Effects Of Atomic Hydrogen And Deuterium Exposure On High Polarization Gaas Photocathodes, M. Baylac, P. Adderley, J. Brittian, J. Clark, T. Day, J. Grames, J. Hansknecht, M. Poelker, M. Stutzman, A. T. Wu, A. S. Terekhov
Effects Of Atomic Hydrogen And Deuterium Exposure On High Polarization Gaas Photocathodes, M. Baylac, P. Adderley, J. Brittian, J. Clark, T. Day, J. Grames, J. Hansknecht, M. Poelker, M. Stutzman, A. T. Wu, A. S. Terekhov
US Department of Energy Publications
Strained-layer GaAs and strained-superlattice GaAs photocathodes are used at Jefferson Laboratory to create high average current beams of highly spin-polarized electrons. High electron yield, or quantum efficiency (QE), is obtained only when the photocathode surface is atomically clean. For years, exposure to atomic hydrogen or deuterium has been the photocathode cleaning technique employed at Jefferson Laboratory. This work demonstrates that atomic hydrogen cleaning is not necessary when precautions are taken to ensure that clean photocathode material from the vendor is not inadvertently dirtied while samples are prepared for installation inside photoemission guns. Moreover, this work demonstrates that QE and beam …
Photoionization And Electron-Impact Ionization Of Xe3+, E. D. Emmons, A. Aguilar, M. F. Gharaibeh, S. W. J. Scully, R. A. Phaneuf, A. L. D. Kilcoyne, A. S. Schlachter, I. Álvarez, C. Cisneros, G. Hinojosa
Photoionization And Electron-Impact Ionization Of Xe3+, E. D. Emmons, A. Aguilar, M. F. Gharaibeh, S. W. J. Scully, R. A. Phaneuf, A. L. D. Kilcoyne, A. S. Schlachter, I. Álvarez, C. Cisneros, G. Hinojosa
US Department of Energy Publications
Photoionization and electron-impact ionization of Xe3+ ions in the region of 4d inner-shell excitation autoionization have been studied using interacting-beam spectroscopic techniques. Absolute cross sections for photoionization of Xe3+ have been obtained and the electron-impact spectrum has been normalized to previously published absolute data. The Xe3+ spectra show large contributions from 4d→nf excitation autoionization processes compared to the lower charge states of Xe due to the significant collapse of the nf wave functions into the ion core as the initial charge state of the ion is increased. In addition, a tentative value for …
Photoexcitation Of A Volume Plasmon In C60 Ions, S. W. J. Scully, E. D. Emmons, M. F. Gharaibeh, R. A. Phaneuf, A. L. D. Kilcoyne, A. S. Schlachter, S. Schippers, A. M. Müller, H. S. Chakraborty, M. E. Madjet, J. M. Rost
Photoexcitation Of A Volume Plasmon In C60 Ions, S. W. J. Scully, E. D. Emmons, M. F. Gharaibeh, R. A. Phaneuf, A. L. D. Kilcoyne, A. S. Schlachter, S. Schippers, A. M. Müller, H. S. Chakraborty, M. E. Madjet, J. M. Rost
US Department of Energy Publications
Neutral C60 is well known to exhibit a giant resonance in its photon absorption spectrum near 20 eV. This is associated with a surface plasmon, where delocalized electrons oscillate as a whole relative to the ionic cage. Absolute photoionization cross-section measurements for C+60, C2+60, and C3+60 ions in the 17– 75 eV energy range show an additional resonance near 40 eV. Time-dependent density functional calculations confirm the collective nature of this feature, which is characterized as a dipole-excited volume plasmon made possible by the special fullerene geometry.
Photoionization Of Multiply Charged Ions At The Advanced Light Source, A. S. Schlachter, A. L. D. Kilcoyne, A. Aguilar, M. F. Gharaibeh, E. D. Emmons, S. W. J. Scully, R. A. Phaneuf, A. M. Müller, S. Schippers, I. Alvarez, C. Cisneros, G. Hinojosa, B. M. Mclaughlin
Photoionization Of Multiply Charged Ions At The Advanced Light Source, A. S. Schlachter, A. L. D. Kilcoyne, A. Aguilar, M. F. Gharaibeh, E. D. Emmons, S. W. J. Scully, R. A. Phaneuf, A. M. Müller, S. Schippers, I. Alvarez, C. Cisneros, G. Hinojosa, B. M. Mclaughlin
US Department of Energy Publications
Photoionization of multiply charged ions is studied using the merged-beams technique at the Advanced Light Source. An ion beam is created using a compact 10-GHz all-permanent-magnet ECR ion source and is accelerated with a small accelerator. The ion beam is merged with a photon beam from an undulator to allow interaction over an extended path. Absolute photoionization cross sections have been measured for a variety of ions along both isoelectronic and isonuclear sequences.
Potential Of Multivariate Quantitative Methods For Delineation And Visualization Of Ecoregions, William Hargrove, Forrest Hoffman
Potential Of Multivariate Quantitative Methods For Delineation And Visualization Of Ecoregions, William Hargrove, Forrest Hoffman
US Department of Energy Publications
Multivariate clustering based on fine spatial resolution maps of elevation, temperature, precipitation, soil characteristics, and solar inputs has been used at several specified levels of division to produce a spectrum of quantitative ecoregion maps for the conterminous United States. The coarse ecoregion divisions accurately capture intuitively-understood regional environmental differences, whereas the finer divisions highlight local condition gradients, ecotones, and clines. Such statistically generated ecoregions can be produced based on user-selected continuous variables, allowing customized regions to be delineated for any specific problem. By creating an objective ecoregion classification, the ecoregion concept is removed from the limitations of human subjectivity, making …
Noncovalent And Nonspecific Molecular Interactions Of Polymers With Multiwalled Carbon Nanotubes, Durairaj Baskaran, Jimmy W. Mays, Matthew S. Bratcher
Noncovalent And Nonspecific Molecular Interactions Of Polymers With Multiwalled Carbon Nanotubes, Durairaj Baskaran, Jimmy W. Mays, Matthew S. Bratcher
US Department of Energy Publications
Polymer composites containing variable amounts of multiwalled carbon nanotubes (MWNTs) have been prepared using solution dispersion and melt-shear mixing. Various polymer composites with 1 wt % MWNTs have been found to dissolve homogeneously in organic solvents. The amount of polymer coated or wrapped MWNTs dissolved in the solution was quantified using UV-vis absorbance at 500 nm and the concentration ratio of [MWNTs]solution/[MWNTs]composite was close to 1. A nonspecific polymer adsorption through multiple-weak molecular interactions of CH groups with MWNTs in the composites has been identified through FTIR spectroscopy. The composites of polybutadiene with different wt % of …
Carbon Nanotubes With Covalently Linked Porphyrin Antennae: Photoinduced Electron Transfer, Durairaj Baskaran, Jimmy W. Mays, X. Peter Zhang, Matthew S. Bratcher
Carbon Nanotubes With Covalently Linked Porphyrin Antennae: Photoinduced Electron Transfer, Durairaj Baskaran, Jimmy W. Mays, X. Peter Zhang, Matthew S. Bratcher
US Department of Energy Publications
Functionalization of carbon nanotubes through surface modification has attracted significant interest recently. Covalent and noncovalent functionalization strategies involving reactions of organic or polymeric molecules onto carbon nanotubes have primarily focused on dispersion or dissolution properties. Incorporation of light absorbing antenna chromophores through a covalent linkage with the extended π electrons of a carbon nanotube would constitute an ideal supramolecular nanoassembly for generating singlet excited energy and its conversion to chemical energy. Porphyrins are one such class of molecules used in assemblies of donor-acceptor materials in molecular electronics and photovoltaic devices.
Several fullerene-based molecular systems with covalently linked porphyrins and metalloporphyrins …
Role Of Branching On The Structure Of Polymer Brushes Formed From Comb Copolymers, Peng Tian, David Uhrig, Jimmy W. Mays, Hiroshi Watanabe, S. Michael Kilbey, Ii
Role Of Branching On The Structure Of Polymer Brushes Formed From Comb Copolymers, Peng Tian, David Uhrig, Jimmy W. Mays, Hiroshi Watanabe, S. Michael Kilbey, Ii
US Department of Energy Publications
The distinguishing feature of a polymer brush at equilibrium is the stretched configuration of the chains that results from tethering the polymer chains by one end at the solid-fluid interface. The stretched configuration of the chains and the crowded nature of the interfacial layer is the origin of many of the useful properties of polymer brushes: these layers resist compression and aggregation, effectively dissipate shear stresses, and respond reversibly to changes in their solution environment.
Radius Of Gyration Of Polystyrene Combs And Centipedes In A Θ Solvent, Ken Terao, Brandon S. Farmer, Yo Nakamura, Hermis Iatrou, Kunlun Hong, Jimmy W. Mays
Radius Of Gyration Of Polystyrene Combs And Centipedes In A Θ Solvent, Ken Terao, Brandon S. Farmer, Yo Nakamura, Hermis Iatrou, Kunlun Hong, Jimmy W. Mays
US Department of Energy Publications
The molecular weight dependence of the radii of gyration Rg in a Θ solvent (trans-decalin) of one regular branched comb and three regular centipede polystyrenes was studied using a gel permeation chromatography system equipped with a two-angle light scattering detector and a refractive index detector. Rg in trans-decalin for each sample of particular molecular weight was about 25% smaller than that in a good solvent (tetrahydrofuran, THF). On the other hand, they are 20-40% larger than the theoretical values from the Gaussian chain model. This difference can be explained with the worm-like comb model developed by Nakamura et …
Maldi-Tof Ms Characterization Of Carboxyl-End-Capped Polystyrenes Synthesized Using Anionic Polymerization, Haining Ji, William K. Nonidez, Rigoberto C. Advincula, Grant D. Smith, S. Michael Kilbey Ii, Mark D. Dadmun, Jimmy W. Mays
Maldi-Tof Ms Characterization Of Carboxyl-End-Capped Polystyrenes Synthesized Using Anionic Polymerization, Haining Ji, William K. Nonidez, Rigoberto C. Advincula, Grant D. Smith, S. Michael Kilbey Ii, Mark D. Dadmun, Jimmy W. Mays
US Department of Energy Publications
A comparative study of three strategies used to synthesize well-defined carboxyl-end-capped polystyrenes is reported. Structural characterization was carried out using a combination of thin-layer chromatography (TLC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). For the reaction of polystyryl anions with 4-bromo-1,1,1-trimethoxybutane, in addition to the major product, Bu-PS-CH2CH2CH2COOH, four byproducts were observed. Their mass values suggest the following structures: Bu-PS-H, Bu-PS-CH3, Bu-PS-CH2CH=CH-CHO, and Bu-PS-CH2CH2CH2- CO-PS-Bu. The reaction of polystyryl anions with succinic anhydride generated the targeted compound, Bu-PS-CO-CH2CH2COOH, …