Publications

1991
J. J. Shim and Johnston, K. P., “MOLECULAR THERMODYNAMICS OF SOLUTE-POLYMER-SUPERCRITICAL FLUID SYSTEMS,” Aiche Journal, vol. 37, pp. 607-616, 1991. Publisher's VersionAbstract
The distribution coefficients of the solutes (toluene, naphthalene, and phenanthrene) are reported at infinite dilution between silicone rubber and supercritical-fluid carbon dioxide. A new technique is described in which a thin film of polymer is coated and cross-linked onto silica, and the distribution coefficient is measured rapidly by elution supercritical-fluid chromatography. Because CO2 significantly enhances the solute’s volatility and its diffusion coefficient in the polymer, it is possible to study solute-polymer interactions at room temperature for nonvolatile compounds which would be difficult to study by conventional techniques such as gas chromatography. These infinite dilution data are used to determine solute-polymer interaction parameters to calculate phase diagrams over a wide concentration range. The residual, combinatorial, and cross-link contributions to the solute activity coefficient in the polymer are discussed as a function of concentration. In addition, pronounced pressure and temperature effects are described in terms of experimentally measured solute partial molar volumes (to - 14 L/mol) and partial molar enthalpies (to - 850 kJ/mol) in the fluid phase.
G. J. McFann and Johnston, K. P., “PHASE-BEHAVIOR OF AOT MICROEMULSIONS IN COMPRESSIBLE LIQUIDS,” Journal of Physical Chemistry, vol. 95, pp. 4889-4896, 1991. Publisher's VersionAbstract
The phase behavior of bis(2-ethylhexyl) sodium sulfosuccinate (AOT)-alkane-brine systems is described over a wide range of pressure, temperature, and salinity for alkanes from ethane to dodecane. The partitioning of AOT between the oil, middle, and brine phases is reported for propane in order to determine the natural curvature. This is important for understanding separation processes with water-in-oil microemulsions. For the lighter, more compressible alkanes, the pressure effect on the hydrophilicity of the surfactant is much larger and in the opposite direction as for the heavier, less compressible ones. In propane at constant temperature and salinity, water-in-oil (w/o) microemulsions have been converted to middle phase microemulsions and then to oil-in-water (o/w) microemulsions by decreasing the pressure. These phase inversions are described in terms of the immiscibilities in the binary systems, and the molecular interactions at the surfactant interface. Although temperature and salinity are used commonly to manipulate interactions primarily on the water side of the interface, these results show it is possible to control interactions on the oil side by adjusting the pressure. The well-established trends in the phase behavior and size of microemulsion drops for dodecane through hexane are not observed for the lighter alkanes. For butane through ethane, a new unusual behavior is identified and attributed to a significant decrease in the strength of the attractive interactions between the surfactant tails and the alkane.
J. J. Shim and Johnston, K. P., “PHASE-EQUILIBRIA, PARTIAL MOLAR ENTHALPIES, AND PARTIAL MOLAR VOLUMES DETERMINED BY SUPERCRITICAL FLUID CHROMATOGRAPHY,” Journal of Physical Chemistry, vol. 95, pp. 353-360, 1991. Publisher's VersionAbstract
A variety of types of thermodynamic properties have been determined at infinite dilution by supercritical fluid chromatography. A key challenge is to identify clearly the retention mechanism. An experimental technique is presented for the measurement of retention due to absorption into a bulk C-18 liquid (stationary) phase, independently of the adsorption on the support. The important effect of the swelling of the liquid phase by the fluid phase is included. Distribution coefficients are presented for naphthalene and phenanthrene between CO2 and the C-18 liquid phase, and used to determine Henry’s constants in the liquid phase and solute partial molar volumes and enthalpies in the fluid phase. In the highly compressible region of CO2 at 35-degrees-C, solute partial molar enthalpies have been found to reach negative values of hundreds of kJ/mol, indicating strongly exothermic solute-solvent clustering.
K. E. Oshea, Combes, J. R., Fox, M. A., and Johnston, K. P., “PHOTOLYSIS OF DIBENZYLKETONES IN SUPERCRITICAL ETHANE AND CARBON-DIOXIDE,” Photochemistry and Photobiology, vol. 54, pp. 571-576, 1991. Publisher's VersionAbstract
The Norrish Type I photofragmentation of two dibenzylic ketones (1,3-diphenyl-2-propanone and 1-(4-methylphenyl)-3-phenyl-2-propanone) in supercritical ethane and carbon dioxide proceeds without evidence for cage recombination of the photogenerated radical pair. A statistical mixture of the bibenzyls formed by random coupling of benzyl and p-xylyl radicals was observed and the first order rate constant for the depletion of the reactant was independent of pressure. These results indicate that solvent cage effects are not operative in these low viscosity supercritical fluids even in the near critical region where solute-solvent clustering is presumably maximal.
K. E. Oshea, Kirmse, K. M., Fox, M. A., and Johnston, K. P., “POLAR AND HYDROGEN-BONDING INTERACTIONS IN SUPERCRITICAL FLUIDS - EFFECTS ON THE TAUTOMERIC EQUILIBRIUM OF 4-(PHENYLAZO)-1-NAPHTHOL,” Journal of Physical Chemistry, vol. 95, pp. 7863-7867, 1991. Publisher's VersionAbstract
The azo-hydrazone tautomeric equilibrium of 4-(phenylazo)-1-naphthol is compared in various liquid and supercritical fluid solvents. The less polar azo tautomer is dominant in the dilute gas phase, compressed ethane, and liquid alkanes. In liquid and supercritical CO2, the equilibrium shifts toward the more polar hydrazone, to yield similar amounts of the two tautomers. This shift is attributed to the Lewis acidity and large quadrupole moment of CO2. The dominance of the hydrazone tautomer in fluoroform (> 90%) can be attributed to that solvent’s large dipole moment and ability to act as a strong electron acceptor (hydrogen bond donor). Since acid-base interactions are prevalent at the lowest pressure studied (1000 psia), changes in the equilibrium constant as a function of pressure have been assigned primarily to increases in the nonspecific polar interactions. The large differences in the polarities, acidities, and basicities of these fluids, despite their similar polarizabilities per volume, are of interest for manipulating chemical processes and for practical applications of supercritical fluid science and technology.
J. F. Bard, “Some Properties of the Bilevel Programming Problem,” J. Optimization Theory and Applications, vol. 68, pp. 371–378, 1991.
R. B. Machemehl and Karachepone, J., “Texas Department of Transportation Final Transportation Planning Division,” 1991.Abstract
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R. B. Machemehl and Acampora, M., “Texas model validation for left-turn phasing alternatives,” 1991.Abstract
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R. B. Machemehl and Acampora, M., “TEXAS MODEL VALIDATION FOR LEFT-TURN PHASING ALTERNATIVES. FINAL REPORT”. 1991.Abstract
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D. G. Peck and Johnston, K. P., “THEORY OF THE PRESSURE EFFECT ON THE CURVATURE AND PHASE-BEHAVIOR OF AOT PROPANE BRINE WATER-IN-OIL MICROEMULSIONS,” Journal of Physical Chemistry, vol. 95, pp. 9549-9556, 1991. Publisher's VersionAbstract
Pressure effects on both the curvature and phase behavior of water-in-oil microemulsions (swollen reverse micelles) are predicted with a unified classical and molecular thermodynamic theory developed by Peck et al. (this issue). The theory is used to identify quantitatively the roles of the intramicellar interfacial interactions and micelle-micelle interactions. A supplementary molecular model is used to calculate the strength of attractive intermicellar interactions over a wide range of conditions, based on previous small-angle neutron-scattering data. An important distinction is made between systems with a small water-to-oil ratio and those where the water-to-oil ratio is much larger, on the order of unity. In the latter the micelle radius is controlled primarily by intramicellar interfacial interactions, specifically the enthalpic propane-surfactant tail interactions. For a small water-to-oil ratio, the micelle radius is limited by attractive micelle-micelle interactions. As pressure increases, the radius increases but eventually reaches a maximum governed by the intramicellar interfacial interactions. There is good agreement between the predictions and experiments over a wide range of water-to-oil ratios.
D. G. Peck, Schechter, R. S., and Johnston, K. P., “UNIFIED CLASSICAL AND MOLECULAR THERMODYNAMIC THEORY OF SPHERICAL WATER-IN-OIL MICROEMULSIONS,” Journal of Physical Chemistry, vol. 95, pp. 9541-9549, 1991. Publisher's VersionAbstract
A unified classical and molecular thermodynamic model is developed in order to predict the phase behavior and interfacial properties of spherical water-in-oil microemulsions. A modified Flory-Krigbaum theory is used to describe the interactions between the surfactant tails and solvent, while the ionic head-group interactions are treated with the Poisson-Boltzman equation. The interfacial tension and the bending moment of the interface are calculated explicitly. These values are incorporated into a classical thermodynamic framework that is forced to satisfy the Gibbs adsorption equation on the interface, guaranteeing thermodynamic consistency. Given a surfactant molecular architecture, the model predicts the size of microemulsion droplets as a function of the chain length of the alkane solvent. For bis(2-ethylhexyl) sodium sulfosuccinate (AOT) in the solvents propane through decane, the calculated trends agree with experiment and are explained mechanistically at the molecular level. The microemulsion radius increases for the solvents pentane through propane, an unusual behavior that is explained theoretically.
1990
C. T. Marcus, Machemehl, R. B., and Lee, C. E., “Auxiliary turning lanes at urban intersections,” 1990.Abstract
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C. T. Marcus, Machemehl, R. B., and Lee, C. E., “AUXILIARY TURNING LANES AT URBAN INTERSECTIONS. FINAL REPORT”. 1990.Abstract
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J. F. Bard and Moore, J. T., A Branch and Bound Algorithm for the Bilevel Programming Problem. SIAM Journal on Scientific and Statistical Computing 11(2) 281-292, 1990.
H. F. Morrison, Nichols, E. A., Torres-Verdín, C., Booker, J. R., and Constable, S. C., “A comparison of magnetotelluric inversion techniques on a mineral prospect in Nevada: (Expanded Abstract): Soc,” Society of Exploration Geophysicists 60th Annual International Meeting. Society of Exploration Geophysicists, San Francisco, CA, 1990.
H. F. Morrison, Nichols, E. A., Torres-Verdín, C., Booker, J. R., and Constable, S. C., “A comparison of magnetotelluric inversion techniques on a mineral prospect in Nevada: (Expanded Abstract): Soc,” Society of Exploration Geophysicists 60th Annual International Meeting. Society of Exploration Geophysicists, San Francisco, CA, 1990.
S. Modur, Machemehl, R. B., and Lee, C. E., Criteria for the Selection of a Left-turn Median Design. Center for Transportation Research, University of Texas at Austin, 1990.Abstract
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S. Modur, Machemehl, R. B., and Lee, C. E., “CRITERIA FOR THE SELECTION OF A LEFT-TURN MEDIAN DESIGN. FINAL REPORT”. 1990.Abstract
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T. A. Edmunds and Bard, J. F., A Decomposition Technique for Discrete Time Optimal Control Problems with an Application to Water Resources Management. Mathematical and Computer Modelling 13(1) 61-78, 1990.
M. A. Middleton, Schechter, R. S., and Johnston, K. P., “DIELECTRIC-PROPERTIES OF ANIONIC AND NONIONIC SURFACTANT MICROEMULSIONS,” Langmuir, vol. 6, pp. 920-928, 1990. Publisher's VersionAbstract
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