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  • 1
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    Design of Nonionic Surfactants for Supercritical Carbon Dioxide (1996)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 1996-12-20
    Description: Interfacially active block copolymer amphiphiles have been synthesized and their self-assembly into micelles in supercritical carbon dioxide (CO2) has been demonstrated with small-angle neutron scattering (SANS). These materials establish the design criteria for molecularly engineered surfactants that can stabilize and disperse otherwise insoluble matter into a CO2 continuous phase. Polystyrene-b-poly(1,1-dihydroperfluorooctyl acrylate) copolymers self-assembled into polydisperse core-shell-type micelles as a result of the disparate solubility characteristics of the different block segments in CO2. These nonionic surfactants for CO2 were shown by SANS to be capable of emulsifying up to 20 percent by weight of a CO2-insoluble hydrocarbon into CO2. This result demonstrates the efficacy of surfactant-modified CO2 in reducing the large volumes of organic and halogenated solvent waste streams released into our environment by solvent-intensive manufacturing and process industries.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McClain -- Betts -- Canelas -- Samulski -- DeSimone -- Londono -- Cochran -- Wignall -- Chillura-Martino -- Triolo -- New York, N.Y. -- Science. 1996 Dec 20;274(5295):2049-52.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉J. B. McClain, D. E. Betts, D. A. Canelas, E. T. Samulski, J. M. DeSimone, Department of Chemistry, University of North Carolina, CB 3290, Venable and Kenan Laboratories, Chapel Hill, NC 27599, USA. J. D. Londono, H. D. Cochran, G. D. Wignall, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA. D. Chillura-Martino and R. Triolo, Departimento di Chimica Fisica, University of Palermo, 90123 Palermo, Italy.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/8953029" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of supercritical water and of supercritical aqueous solutions (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5606-5621 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics (MD) calculations have been performed to determine equilibrium structure and properties of systems modeling supercritical (SC) water and SC aqueous solutions at two states near the critical point using the simple point charge (SPC) potential model of Berendsen et al. for water. Both thermodynamic and dielectric properties from the simulations for pure water are accurate in comparison with experimental results even though the SPC model parameters were fitted to properties of ambient water. Details of the near-critical clustering in SC water have been predicted which have not been measured to date. MD studies have also been undertaken of systems that model sodium and chloride ions and neutral argon in SC water at the same states. The first solvation shell in SC water is observed to be similar to that in ambient water, and long-range solvation structures in SC water are similar to those observed for simple SC solvents. An excess of water molecules is observed clustering around ionic solutes which behave attractively and a deficit is observed around neutral atomic solutes which behave repulsively. These results should be helpful in developing a qualitative understanding of important processes that occur in SC water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460497
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  • 3
    Electronic Resource
    Electronic Resource
    Small angle neutron scattering studies of dilute supercritical solutions. I. Pure supercritical neon (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 466-470 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Small angle neutron scattering (SANS) results are presented for states of neon close to the critical isochore and supercritical temperatures between 47 and 60 K. The net intensities were converted to absolute units of differential cross section per unit sample volume by comparison with precalibrated secondary standards. The values of the differential cross section at zero scattering vector are in excellent agreement with values calculated from an equation of state. Evidence of three-body forces in these data are compared to that present in Krypton data reported earlier. It is concluded that small angle experiments of the sort reported here should be repeated for the heavier noble gases, for which effects from three-body forces are anticipated to be larger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465770
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  • 4
    Electronic Resource
    Electronic Resource
    Cryogenic apparatus for scattering and phase equilibrium studies (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 200-202 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A cryogenic apparatus has been developed for neutron scattering and phase equilibrium studies on supercritical inert gas mixtures. Scattering and phase equilibrium studies can be performed in the same apparatus; the whole apparatus is transportable to any scattering facility. It centers on a stirred, batch, view cell of unique design. By changing only three parts of simple design (two windows, one sample cylinder) to an appropriate material, this apparatus can be used for studies involving wide or small angle scattering of neutrons or x rays. Its use can also be extended to pure fluids, liquids, and states away from the critical point. It operates within pressure and temperature ranges of 0–13.8 MPa and 20–300 K. To our knowledge this is the first neutron scattering cell with axial fluid mixing and with a temperature gradient of 10 mK or less over a large sample volume (1-cm diameter, 5-cm long). The accuracy and performance of the apparatus was tested on pure neon by reproducing its saturation curve and by performing small angle neutron scattering on some supercritical states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144434
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  • 5
    Electronic Resource
    Electronic Resource
    Na+–Cl− ion pair association in supercritical water (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 9379-9387 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular dynamics simulations of supercritical electrolyte solutions with three different ion–water models are performed to study the anion–cation potential of mean force of an infinitely dilute aqueous NaCl solution in the vicinity of the solvent's critical point. The association constant for the ion pair Na+/Cl− and the constant of equilibrium between the solvent-separated and the contact ion pairs are determined for three models at the solvent critical density and 5% above its critical temperature. The realism of the aqueous electrolyte models is assessed by comparing the association constants obtained by simulation with those based on high temperature conductance measurements. Some remarks are given concerning the calculation of the mean-force potential from simulation and the impact of the assumptions involved. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470707
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  • 6
    Electronic Resource
    Electronic Resource
    Multiple time step nonequilibrium molecular dynamics simulation of the rheological properties of liquid n-decane (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 255-262 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonequilibrium and equilibrium molecular dynamics simulations are reported for a united-atom model of n-decane at a state point in the liquid phase. The viscosity calculated by our nonequilibrium molecular dynamics simulations is in good agreement with that obtained from our equilibrium molecular dynamics simulations via the Green–Kubo relation and with that obtained by Mundy et al. [J. Chem. Phys. 102, 3776 (1995)] using the same potential model at the same state conditions. Additionally, the viscosity calculated by nonequilibrium molecular dynamics is in very good agreement with experimental results for n-decane. The algorithm used for the equilibrium molecular dynamics simulations is an application to alkanes of the multitime step Nosé dynamics algorithm developed by Tuckerman and Berne. For the nonequilibrium molecular dynamics simulations, an extension of the multitime step method is derived for the nonequilibrium equations of motion describing planar Couette flow with Nosé thermostat. The contributions of the intramolecular interactions to the stress tensor and its relaxation have been analyzed; the bond stretching motions play a dominant role in the short-time behavior of the atomic stress–stress correlation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470896
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  • 7
    Electronic Resource
    Electronic Resource
    Molecular dynamics simulations of the rheology of normal decane, hexadecane, and tetracosane (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1214-1220 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Extensive nonequilibrium molecular dynamics simulations have been carried out for liquid decane, hexadecane, and tetracosane at densities corresponding to atmospheric pressure and near ambient temperatures. The strain-rate-dependent viscosity has been obtained for strain rates ranging over several orders of magnitude. At high strain rate, the viscosities for all alkanes studied here have similar values and exhibit similar power-law shear-thinning behavior with a slope between about −0.40 and −0.33. Accompanying this shear thinning is the onset of orientational order and the alignment of the alkane molecules with the flow direction. The alignment angle tends to 45° at very low strain rate and is significantly smaller at high strain rate. This suggests that the chains substantially align in the flow direction and that the dominant motion at high strain rate is the sliding of the chains parallel to the flow. At low strain rate, the shear viscosity shows a transition to Newtonian behavior. The Newtonian viscosity can be obtained from the plateau value of the shear viscosity at the lowest strain rates calculated from the nonequilibrium molecular dynamics simulation (NEMD). This is demonstrated by comparing the viscosity of decane obtained by extrapolating the NEMD simulation with an independent calculation using the standard Green–Kubo method. The transition from the non-Newtonian regime to the Newtonian regime is also correlated with the disappearance of orientational order and with the longest relaxation time of the liquid alkanes simulated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471971
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  • 8
    Electronic Resource
    Electronic Resource
    Hyperfiltration. Processing of pulp mill sulfite wastes with a membrane dynamically formed from feed constituents (1967)
    s.l. : American Chemical Society
    Environmental science & technology 1 (1967), S. 991-996 
    Details
    ISSN: 1520-5851
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/es60012a004
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  • 9
    Electronic Resource
    Electronic Resource
    Solubility of solid carbon tetrachloride in supercritical carbon tetrafluoride (1991)
    s.l. : American Chemical Society
    Journal of chemical & engineering data 36 (1991), S. 99-102 
    Details
    ISSN: 1520-5134
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/je00001a030
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  • 10
    Electronic Resource
    Electronic Resource
    Shear behavior of squalane and tetracosane under extreme confinement. II. Confined film structure (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10327-10334 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper focuses on the structural characteristics of confined squalane and tetracosane under shear flow conditions. Nonequilibrium molecular dynamics simulation is used to explore the rheology of these model lubricants. A preceding paper describes the molecular model and the simulation method, and examines interfacial slip. The lubricants are confined between model walls that have short chains tethered to them, thus screening the wall details. In this paper we examine the density profiles and chain conformations of the alkanes under shear flow conditions. Our results indicate a profound influence of the walls on the fluid structure. In particular, when the wall spacing is close to an integral multiple of the molecular diameter, tetracosane shows the formation of distinct layers with the molecules being in a fully extended state. This behavior is not observed for squalane. Under shear flow conditions the molecules tend to orient parallel to the walls, as would be expected, with a greater degree of orientation (a) close to the walls, (b) at the positions of local density maxima, and (c) at higher strain rates. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474172
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