308 Matching Results

Search Results

Advanced search parameters have been applied.

Corner rounding in EUV photoresist: tuning through molecular weight, PAG size, and development time

Description: In this paper, the corner rounding bias of a commercially available extreme ultraviolet photoresist is monitored as molecular weight, photoacid generator (PAG) size, and development time are varied. These experiments show that PAG size influences corner biasing while molecular weight and development time do not. Large PAGs are shown to exhibit less corner biasing, and in some cases, lower corner rounding, than small PAGs. In addition, heavier resist polymers are shown to exhibit less corner rounding than lighter ones.
Date: December 31, 2009
Creator: Anderson, Christopher; Daggett, Joe & Naulleau, Patrick
Partner: UNT Libraries Government Documents Department

Physics group progress report, May 1--31, 1948

Description: Various studies conducted at Mound Laboratory concerning physical properties of postum (Polonium 210) are described. Some studies are entitled Purity of Postum (Vacuum Balance Method); Vapor Pressure of Postum; X-ray Studies; Vapor Pressure by Effusion; Molecular Weigh of Postum; and Weighing Procedures for Macroassay.
Date: December 31, 1948
Creator: Knauss, H.P.
Partner: UNT Libraries Government Documents Department


Description: The dependence of an acoustically resonant optoacoustic signal on the molecular weight, and thermodynamic and transport properties of the buffer gas is reported. Our results show that careful selection of such gases can significantly increase the sensitivity and flexibility of optoacoustic spectroscopy. We also demonstrate that such thermodynamic quantities as {gamma} ({triple_bond} C{sub p}/C{sub v}) and sound velocity can now be measured readily and accurately. Other potential applications are suggested.
Date: November 1, 1977
Creator: Thomas III, L.J.; Kelly, M.J. & Amer, N.M.
Partner: UNT Libraries Government Documents Department

EOSN: A TOUGH2 module for noble gases

Description: We developed a new fluid property module for TOUGH2, called EOSN, to simulate transport of noble gases in the subsurface. Currently, users may select any of five different noble gases as well as CO2, two at a time. For the three gas components (air and two user-specified noble gases) in EOSN, the Henry's coefficients and the diffusivities in the gas phase are no longer assumed constants, but are temperature dependent. We used the Crovetto et al. (1982) model to estimate Henry's coefficients, and the Reid et al. (1987) correlations to calculate gas phase diffusivities. The new module requires users to provide names of the selected noble gases, which properties are provided internally. There are options for users to specify any (non-zero) molecular weights and half-lives for the gas components. We provide two examples to show applications of TOUGH2IEOSN. While temperature effects are relatively insignificant for one example problem where advection is dominant, they cause almost an order of magnitude difference for the other case where diffusion becomes a dominant process and temperature variations are relatively large. It appears that thermodynamic effects on gas diffusivities and Henry's coefficients can be important for low-permeability porous media and zones with large temperature variations.
Date: March 7, 2003
Creator: Shan, Chao & Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Rh(I)-Catalyzed Arylation of Heterocycles via C-H Bond Activation: Expanded Scope Through Mechanistic Insight

Description: A practical, functional group tolerant method for the Rh-catalyzed direct arylation of a variety of pharmaceutically important azoles with aryl bromides is described. Many of the successful azole and aryl bromide coupling partners are not compatible with methods for the direct arylation of heterocycles using Pd(0) or Cu(I) catalysts. The readily prepared, low molecular weight ligand, Z-1-tert-butyl-2,3,6,7-tetrahydrophosphepine, which coordinates to Rh in a bidentate P-olefin fashion to provide a highly active yet thermally stable arylation catalyst, is essential to the success of this method. By using the tetrafluoroborate salt of the corresponding phosphonium, the reactions can be assembled outside of a glove box without purification of reagents or solvent. The reactions are also conducted in THF or dioxane, which greatly simplifies product isolation relative to most other methods for direct arylation of azoles employing high-boiling amide solvents. The reactions are performed with heating in a microwave reactor to obtain excellent product yields in two hours.
Date: July 18, 2007
Creator: Lewis, Jared; Berman, Ashley; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department


Description: Samples of ultrahigh molecular weight polyethylene (UHMW-PE), polytetrafluoroethylene (PTFE), and the polyimide Vespel{reg_sign} were exposed to tritium gas in closed containers initially at 101 kPa (1 atmosphere) pressure and ambient temperature for various times up to 2.3 years. Tritium exposure effects on the samples were characterized by dynamic mechanical analysis (DMA) and radiolysis products were characterized by measuring the total final pressure and composition in the exposure containers at the end of exposure period.
Date: November 1, 2006
Creator: Clark, E & Kirk Shanahan, K
Partner: UNT Libraries Government Documents Department

Compulsory Deep Mixing of 3He and CNO Isotopes on the First Giant Branch

Description: We have found a deep-mixing process which occurs during First Giant Branch (FGB) evolution. It begins at the point in evolution where the surface convection zone (SCZ), having previously grown in size, starts to shrink, and it is driven by a local minimum that develops in the mean molecular weight as a result of the burning of {sup 3}He. This mixing can solve two important observational problems. One is why the interstellar medium (ISM) has not been considerably enriched in {sup 3}He since the Big Bang. The other is why products of nucleosynthesis such as {sup 13}C are progressively enriched on the upper FGB, when classical stellar modeling says that no further enrichment should take beyond the First Dredge-Up (FDU) episode, somewhat below the middle of the FGB.
Date: July 26, 2007
Creator: Eggleton, P P; Dearborn, D P & Lattanzio, J
Partner: UNT Libraries Government Documents Department

Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of low-mass Red Giants

Description: Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the {sup 3}He({sup 3}He,2p){sup 4}He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It not only eliminates the problem of {sup 3}He overproduction, reconciling stellar and big bang nucleosynthesis with observations, but solves the discrepancy between observed and calculated CNO isotope ratios in low mass giants, a problem of more than 3 decades standing. This mixing mechanism operates rapidly once the hydrogen burning shell approaches the material homogenized by the surface convection zone. In agreement with observations, Pop I stars between 0.8 and 2.0 M{sub {circle_dot}} develop {sup 12}C/{sup 13}C ratios of 14.5 {+-} 1.5, while Pop II stars process the carbon to ratios of 4.0 {+-} 0.5. In stars less than 1.25 M{sub {circle_dot}}, this mechanism also destroys 90% to 95% of the {sup 3}He produced on the main sequence.
Date: March 20, 2007
Creator: Eggleton, P P; Dearborn, D P & Lattanzio, J C
Partner: UNT Libraries Government Documents Department

Evaluation of a novel UHMWPE bearing for applications in precision slideways

Description: This paper presents a novel slideway bearing design comprised of a thin-film (0.1 mm-0.2 mm) of ultra-high molecular weight polyethylene (UHMWPE) bound to a rigid hemispherical substrate. Two prototype bearing designs were fabricated and tested to characterize the coefficient of friction (dynamic and static) and wear of the polymer. In addition, similar bearings were incorporated into a kinematically constrained rectilinear carriage to determine the repeatability of motion during multiple traverses. The first bearing had a radius of curvature on the order of 2.38 mm incorporating an UHMWPE film thickness between 0.1 mm and 0.2 mm. The friction coefficient was measured to be between 0.155 and 0.189 for normal loads of 11.5 N and 2.2 N, respectively at a surface speed of 4.2 mm {center_dot} s{sup -1}. This bearing failed after a traverse of approximately 700 m at a load of 11.5 N. A similar evaluation procedure was carried out on a bearing of radius 6.35 mm resulting in a friction coefficient between 0.125 and 0.185 at loads of 27.8 N and 2.2 N, respectively, and the bearing endured a traverse of over 2.2 km at a load of approximately 28 N (in both air and vacuum conditions) with a surface speed of 4.2 mm {center_dot} s{sup -1}. The second bearing prototype was further subjected to a repeatability test. In this setup, a carriage incorporating five bearings was traversed in a nominally linear path while vertical deviations for multiple traverses were measured by a custom built displacement sensor. Deviations from a linear path were observed to repeat to within a few nanometers about nominal variations of less than 10 nm for a traverse distance of 10 mm. This system and other subsystems used to characterize the friction coefficient and noise of the polymer bearing are presented.
Date: March 8, 2005
Creator: Buice, E S; Yang, H; Smith, S T; Hocken, R J & Seugling, R M
Partner: UNT Libraries Government Documents Department

"Smart" Multifunctional Polymers for Enhanced Oil Recovery

Description: Recent recommendations made by the Department of Energy, in conjunction with ongoing research at the University of Southern Mississippi, have signified a need for the development of 'smart' multi-functional polymers (SMFPs) for Enhanced Oil Recovery (EOR) processes. Herein we summarize research from the period of September 2003 through March 2007 focusing on both Type I and Type II SMFPs. We have demonstrated the synthesis and behavior of materials that can respond in situ to stimuli (ionic strength, pH, temperature, and shear stress). In particular, Type I SMFPs reversibly form micelles in water and have the potential to be utilized in applications that serve to lower interfacial tension at the oil/water interface, resulting in emulsification of oil. Type II SMFPs, which consist of high molecular weight polymers, have been synthesized and have prospective applications related to the modification of fluid viscosity during the recovery process. Through the utilization of these advanced 'smart' polymers, the ability to recover more of the original oil in place and a larger portion of that by-passed or deemed 'unrecoverable' by conventional chemical flooding should be possible.
Date: March 20, 2007
Creator: McCormick, Charles & Lowe, Andrew
Partner: UNT Libraries Government Documents Department

Forced convection and transport effects during hyperbaric laser chemical vapor deposition

Description: This work explores mass transport processes during HP-LCYD, including the transverse forced-flow of precursor gases through a nozzle to enhance fiber growth rates. The use of laser trapping and suspension of nano-scale particles in the precursor flow is also described, providing insights into the nature of the gas flow, including jetting from the fiber tip and thermodiffusion processes near the reaction zone. The effects of differing molecular-weight buffer gases is also explored in conjunction with the Soret effect, and it is found that nucleation at the deposit surface (and homogeneous nucleation in the gas phase) can be enhanced/ retarded, depending on the buffer gas molecular weight. To demonstrate that extensive microstructures can be grown simultaneously, three-dimensional fiber arrays are also grown in-parallel using diffractive optics--without delatory effects from neighboring reaction sites.
Date: January 1, 2009
Creator: Maxwell, James L; Chavez, Craig A; Espinoza, Miguel; Black, Marcie; Maskaly, Karlene & Boman, Mats
Partner: UNT Libraries Government Documents Department

Probing Structure Property Relationships in Complex Engineering Silicones by 1H NMR

Description: It is generally accepted that the properties of polymeric materials are controlled by the network structure and the reactions by which they have been constructed. These properties include the bulk moduli at creation, but also the properties as a function of age during use. In order to interpret mechanical properties and predict the time dependent changes in these properties, detailed knowledge of the effect of structural changes must be obtained. The degree and type of crosslinking, the molecular weight between crosslinks, the number of elastically ineffective chains (loops, dangling chain ends, sol-fraction) must be characterized. A number of theoretical and experimental efforts have been reported in the last few years on model networks prepared by endlinking reactions and the relationships of those structures with the ultimate mechanical properties. A range of experimental methods have been used to investigate structure including rheometric, scattering, infrared, {sup 29}Si MAS and CPMAS, {sup 1}H relaxation measurements, and recently {sup 1}H multiple quantum methods. Characterization of the growth of multiple quantum coherences have recently been shown to provide detailed insight into silicone network structure by the ability to selective probe the individual components of the polymer network, such as the polymer-filler interface or network chains. We have employed recently developed MQ methods to investigate the structure-property relationships in a series of complex, endlinked filled-PDMS blends. Here, a systematic study of the relationship between the molecular formulation, as dictated by the amount and type of crosslinks present and by the remaining network chains, and the segmental dynamics as observed by MQ NMR was performed.
Date: July 14, 2006
Creator: Chinn, S C; Gjersing, E L; Maxwell, R S; Eastwood, E; Bowen, D & Stephens, T
Partner: UNT Libraries Government Documents Department

Modeling Emissions of Volatile Organic Compounds from New Carpets

Description: A simple model is proposed to account for observed emissions of volatile organic compounds (VOCs) from new carpets. The model assumes that the VOCs originate predominantly in a uniform slab of polymer backing material. Parameters for the model (the initial concentration of a VOC in the polymer, a diffusion coefficient and an equilibrium polymer/air partition coefficient) are obtained from experimental data produced by a previous chamber study. The diffusion coefficients generally decrease as the molecular weight of the VOCs increase, while the polymer/air partition coefficients generally increase as the vapor pressure of the compounds decrease. In addition, for two of the study carpets that have a styrene-butadiene rubber (SBR) backing, the diffusion and partition coefficients are similar to independently reported values for SBR. The results suggest that predictions of VOCs emissions from new carpets may be possible based solely on a knowledge of the physical properties of the relevant compounds and the carpet backing material. However, a more rigorous validation of the model is desirable.
Date: February 1, 1993
Creator: Little, J.C.; Hodgson, A.T. & Gadgil, A.J.
Partner: UNT Libraries Government Documents Department


Description: The research outlined below established theoretical proof-of-concept using ab initio calculations that {sup 3}He can be separated from {sup 4}He by taking advantage of weak van der Waals interactions with other higher molecular weight rare gases such as xenon. To the best of our knowledge, this is the only suggested method that exploits the physical differences of the isotopes using a chemical interaction.
Date: September 4, 2012
Creator: Roy, L.; Nigg, H. & Watson, H.
Partner: UNT Libraries Government Documents Department

Static and Flow Properties of Dilute Polymer Solutions

Description: Small weight percentages of certain high-molecular weight polymers added to liquids in turbulent flow through conduits can result in dramatic friction reduction. Although many current and potential uses of the drag reduction phenomenon exist, there is a fundamental problem: drag reduction efficacy decreases rapidly with flow time due to the mechanical degradation in flow of the added polymer. In this thesis study, dilute aqueous solutions of polyacrylamide were tested under turbulent flow conditions in an attempt to determine where mechanical degradation in flow occurs.
Date: August 1991
Creator: Whang, Kyu-ho
Partner: UNT Libraries

Degradation kinetics of polymers in solution: Time-dependence of molecular weight distributions. [Quarterly report, January--March 1996]

Description: Polymer degradation occurs when polymer chains are broken under the influence of thermal, mechanical, or chemical energy. Chain-end depolymerization and random- and midpoint-chain scission are mechanisms that have been observed in liquid-phase polymer degradation. Here we develop mathematical models, unified by continuous-mixture kinetics, to show how these different mechanisms affect polymer degradation in solution. Rate expressions for the fragmentation of molecular-weight distributions (MWDs) govern the evolution of the MWDs. The governing integro-differential equations can be solved analytically for realistic conditions. Moment analysis for first-order continuous kinetics shows the temporal behavior of MWDs. Chain-end depolymerization yields monomer product and polymer molecular-weight moments that vary linearly with time. In contrast, random- and midpoint-chain scission models display exponential time behavior. The mathematical results reasonably portray experimental observations for polymer degradation. This approach, based on the time evolution of continuous distributions of chain length or molecular weight, provides a framework for interpreting several types of polymer degradation processes.
Date: February 27, 1996
Creator: McCoy, B.J. & Madras, G.
Partner: UNT Libraries Government Documents Department

Detection of Biological Materials Using Ion Mobility Spectroscopy

Description: Traditionally, Ion Mobility Spectroscopy has been used to examine ions of relatively low molecular weight and high ion mobility. In recent years, however, biomolecules such as bradykinin, cytochrome c, bovine pancreatic trypsin inhibitor (BPTI), apomyoglobin, and lysozyme, have been successfully analyzed, but studies of whole bio-organisms have not been performed. In this study an attempt was made to detect and measure the mobility of two bacteriophages, {lambda}-phage and MS2 using electrospray methods to inject the viruses into the ion mobility spectrometer. Using data from Yeh, et al., which makes a comparison between the diameter of non-biologic particles and the specific particle mobility, the particle mobility for the MS2 virus was estimated to be 10{sup {minus}2} cm{sup 2}/volt-sec. From this mobility the drift time of these particles in our spectrometer was calculated to be approximately 65 msec. The particle mobility for the {lambda}-phage virus was estimated to be 10{sup {minus}3} cm{sup 2}/volt-sec. which would result in a drift time of 0.7 sec. Spectra showing the presence of a viral peak at the expected drift time were not observed. However, changes in the reactant ion peak that could be directly attributed to the presence of the viruses were observed. Virus clustering, excessive collisions, and the electrospray injection method limited the performance of this IMS. However, we believe that an instrument specifically designed to analyze such bioagents and utilizing other injection and ionization methods will succeed in directly detecting viruses and bacteria.
Date: March 1, 1999
Creator: Rodacy, P.J.; Sterling, J.P. & Butler, M.A.
Partner: UNT Libraries Government Documents Department

Characterization of asphaltenes from processed resids

Description: The current and future trend for petroleum processing is towards conversion of heavier and heavier fractions into useful products such as gasoline and diesel. Asphaltenes, the heptane insoluble fraction of heavy oils, are a solubility class and not a specific boiling range. They tend to be the hardest fraction to process in the refinery because of their high molecular mass, aromaticity and heteroatom and metal (S, N, Ni, V) content. Molecular characterization of asphaltenes is important since a more thorough understanding of the chemical nature of the constituents should lead to more efficient processing schemes. A major hurdle in the accurate representation of the molecular structure of asphaltenes has been the determination of the molecular weight. The main problem is the formation of molecular aggregates depending upon factors such as polarity of the solvent, temperature, concentration and others. Over the past 15 years or so, the apparent molecular weight of asphaltenes has dropped significantly lower as the cause and effect of aggregation on molecular weight was determined. Molecular weights as high as 500,000 have been reported for some asphaltenes in the past with weights as low as 600 appearing in the literature recently depending on the analytical method used. In this study, high resolution sector field mass spectrometry was used to determine the comparative speciation of the composition of the asphaltenes from resid subjected to processing conditions.
Date: April 1, 1997
Creator: Hunt, J.E.; Winans, R.E. & Miller, J.T.
Partner: UNT Libraries Government Documents Department

Factor analysis of GPC-FTIR data in PBX9501 binder degradation studies

Description: The GPC/FTIR data consist of sets of 120 FTIR spectra corresponding to 120 GPC fractions. The GPC fractions can be further categorized by their polystyrene equivalent molecular weight and retention time, The FTIR data to be compared is in three sets of 120 spectra corresponding to the control, thermally aged, and radiolytically aged binder material. Figure 1 shows the extracted spectra (or factors) and corresponding concentration profiles (or scores) for the control data set. The four extracted spectra correspond to spectra for the background/baseline, Estane, Irganox, and NP. The extracted spectra match the spectra of pure components with the exception of Irganox. The Irganox spectrum has some spectral features corresponding to Irganox, but others are due to the poor signal-to-noise in the spectra of these GPC fractions. The low concentration for Irganox results in a widely varying concentration profile and the poor extracted spectrum. The factors and scores for the thermally aged data set demonstrate the same components that are evident in the control data set. The concentration profile shows an asymmetric distribution for Estane with a tail on the low molecular weight side. Less NP is associated with Estane in this region compared to the control data. The major NP concentration is near fraction 80, but is considerably less in magnitude (relative to Estane) when compared to the control. For the radiolytically aged sample set a five-factor solution provides a better fit for the data. The primary difference is the presence of additional bands near 1050,1320, and 1560 cm{sup {minus}1} for factor 5. Factor 5 shows concentration primarily in the same region as Estane.
Date: November 1, 2000
Creator: Schoonover, J. & Bridgewater, J.
Partner: UNT Libraries Government Documents Department

Structure of charged polymer chains in confined geometry.

Description: The intra- and interchain structure of sodium poly(styrenesulphonate) when free and when confined in contrast matched porous Vycor has been investigated by SANS. When confined, a peak is observed whose intensity increases with molecular weight and the 1/q scattering region is extended compared to the bulk. We infer that the chains are sufficiently extended, under the influence of confinement, to highlight the large scale disordered structure of Vycor. The asymptotic behavior of the observed interchain structure factor is = 1/q{sup 2} and = 1/q for free and confined chains respectively.
Date: December 15, 2000
Creator: Gilbert, E. P.; Auvray, L. & Lal, J.
Partner: UNT Libraries Government Documents Department


Description: This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). This project addresses fundamental questions concerning the behavior of polymers at interfaces: (1) What processes control the formation of an adsorbed layer on a clean surface? (2) What processes control the displacement of preadsorbed polymers? (3) Can one accurately predict the structure of polymer layers? To answer these questions, using neutron reflectivity, we have studied adsorbed layers of the polymer poly(methyl methacrylate) (PMMA) onto a quartz substrate. The polymer density profiles were derived from the neutron reflectivity data. We have shown that dry films exhibit behavior predicted by mean-field theory in that the equilibrated layer thickness scales with the molecular weight of the polymer. Also, we find that the profiles of the polymers in solution qualitatively agree with those predicted by reflected random walk (RRW) theories, yet the profiles are not in quantitative agreement.
Date: November 1, 1999
Creator: SMITH, G.S.; MAJEWSKI, J. & AL, ET
Partner: UNT Libraries Government Documents Department