ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
An electrostatic theory for the equilibrium properties of a mixture of equisized ions and dipoles is developed by solving the Debye–Hückel differential equation for the cases of a charge and a dipole, respectively, in a dielectric continuum that contains free charges. This theory yields expressions for the potentials of mean force of ion-ion, ion-dipole, and dipole-dipole interactions. Furthermore, it leads to a formula for the dielectric constant that modifies Onsager's result by accounting not only for the dipoles, but also for the free ions, and resembles the expression obtained by Adelman and Chen. The theory is applied to calculate thermodynamic properties of the model system of equisized charged hard spheres in a dielectric continuum (restricted primitive model), approximating dipolar ion pairs as spheres. We thus augment the work of Fisher and Levin, who added a shielded dipole-ion interaction term to the traditional Debye–Hückel theory, for a shielded dipole-dipole interaction and a density-dependent dielectric constant. The approximate evaluation of this theory yields a narrowing of the coexistence curve compared to the Fisher–Levin theory along with a considerable decrease of the critical density; however, it does not lead to the dramatic increase of the critical temperature that was observed by Guillot and Guissani who modified the Fisher–Levin theory by including unscreened dipole-dipole interactions adopting the original Onsager theory. © 1998 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.476210
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