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  • 1
    Electronic Resource
    Electronic Resource
    Coulombic and non-Coulombic contributions to the criticality of ionic fluids. An experimental approach (1995)
    Springer
    Journal of statistical physics 78 (1995), S. 169-196 
    Details
    ISSN: 1572-9613
    Keywords: Phase separations ; critical phenomena ; critical exponents ; ionic fluids ; electrolyte solutions ; light scattering ; intermolecuar interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The recent discovery of liquid-liquid phase separations in electrolyte solutions with critical points near room temperature enables the systematic study of the critical behavior of ionic fluids. Depending on the nature of the molecular interactions, either sharp mean-field or Ising behavior is obtained in the temperature range down tot=(T−T c )/T c =10−4 or less. Mean-field-like criticality is obtained with systems which in the framework of a simple corresponding states model are fairly close to the critical point of the “restricted primitive model” (RPM) of equally-sized charged spheres in a dielectric continuum. In these cases the phase separation is driven by the Coulombic forces (so-calledCoulombic phase separations). This type of unmixing occurs for 1∶1 electrolytes in solvents of low dielectric constant. Simple mechanisms for unmixing suggested in the literature are discussed in relation to the available data. Some evidence for departures from the simple RPM prediction is found. The presence of additional short-range interactions leads to sharp Ising behavior. Examples are solutions of tetraalkylammonium salts in water and other highly structured solvents, where phase separation results from the peculiar solvophobic nature of ions (solvophobic phase separations). Previous speculations that this type of unmixing shows the tendency toward closed loops are confirmed by the first direct observation of a lower consolute point in an aqueous solution of propyl-tributylammonium iodide. By light scattering studies and measurements of the coexistence curve near the upper and lower consolute points Ising criticality is confirmed. A new mechanism for phase separation is reported for the system ethylammonium nitrate+octanol, where ion pairs are stabilized by hydrogen bonding beyond what is expected from the RPM. This comparatively subtle additional interaction (so-calledstricky ions) already changes the behavior of otherwise RPM-like systems from mean-field to Ising criticality. The results are discussed with particular emphasis on their implications for possible scenarios for explaining a mean-field critical point or crossover from mean-field to Ising behavior beyond the accessible temperature range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02183345
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Light-scattering investigations of the liquid-liquid phase transition of the ionic system: Trimethylethyl-ammonium bromide in chloroform (1994)
    Springer
    International journal of thermophysics 15 (1994), S. 1045-1056 
    Details
    ISSN: 1572-9567
    Keywords: chloroform ; critical phenomena ; ionic solution ; light scattering ; liquid-liquid phase transition ; ternary mixture ; trimethylethyl-ammonium bromide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Phase diagrams and light-scattering measurements of solutions of trimethylethyl-ammonium bromide in chloroform (ε=4.72 at 25 C) with an ethanol content of 1% are reported. The system has a lower critical point nearT = 25°C. The critical mole fraction is xc,=0.0503 ± 0.0002, which corresponds to the reduced variablesT c * =0.036 andc c * =0.029 of therestricted primitive model (RPM) and is slightly below the values predicted by the RPM for the critical parameters. The analysis of the scattering intensity at critical composition gives v = 0.631 ± 0.003 for the critical exponent of the correlation length Σ with an amplitude of 0.87± 0.01 nm. The system, a solution of a salt of essentially spherical ions of almost equal size in a simple low-dielectric polar liquid, with critical parameters very close to predictions of the RPM, nevertheless has an Ising critical point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01458814
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    Paper (German National Licenses)
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