ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
We report on data for the concentration dependence of the static dielectric constant cursive-epsilonS of solutions of tetra-n-butylammonium naphtylsulfonate (TBNAS) in toluene derived from measurements of the frequency-dependent complex permittivity. The system shows an upper consolute point at Tc=329 K and a mole fraction Xc=0.0235 of the salt. The measurements were performed along a slightly supercritical isotherm at 338.15 K at mole fractions 0.01≤X≤0.068. cursive-epsilonS increases with increasing salt concentration. At the critical point cursive-epsilonS=(3.1±0.05) compared with cursive-epsilonS=2.35 for pure toluene. In the concentration range covered by the experiments, the effective dipole moments calculated from these data are of the order of μeff=5 D, which is distinctly lower than an estimate for the isolated molecule, μ0≅18 D. The difference is attributed to compensation effects due to preferred antiparallel ion pair orientations, as described by a Kirkwood–Fröhlich-type theory with correlation factors of gK〈1. At the critical point we find gK≅0.05. Due to these orientational correlations, dipole–dipole interactions between ion pairs may provide a significantly smaller contribution to the free energy than predicted by theory. This may explain the good performance of theories that ignore dipole–dipole interactions between pairs. © 2001 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1349093
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