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This study assessed the relative merits of the Derjaguin--Landau--Verwey--Overbeek and Sogami--Ise theories for the description of the electrostatic interaction between like-charged colloid particles in an electrolyte solution, which differ qualitatively in their predictions of the nature of this interaction. The former implies a repulsion at all distances with a screened-Coulomb (or Yukawa-type) dependence on distance, whereas the latter leads to an electrolyte-mediated, long-range attraction. The Sogami-Ise result for the interaction potential depends critically on the notion that the electrostatic parts of the Helmholtz and Gibbs energies of an electrolyte solution are different. By elaborating on the thermodynamic implications of this assumption, it was determined that it leads to a conflict with well-established results, in particular the relation between osmotic pressure and solvent chemical potential, already at the Debye-Huckel level. For this reason alone, the Sogami--Ise theory is untenable. The condensation and ordering phenomena observed with charged colloids in low-ionic-strength solutions, which the Sogami--Ise theory was originally designed to explain, can be interpreted without the need to resort to long-range electrostatic attraction, as has been demonstrated in previously published work. Abbreviations: DH, Debye-Huckel; DLVO, Derjaguin--Landau--Verwey--Overbeek; SI, Sogami--Ise. doi:10.2136/sssaj2009.0224

Evidence for the competition between long-range electron transfer across self-assembled monolayers (SAMs) and incorporation of the redox probe into the film is reported for the electroreducion of Ru[NH(sub 3)](sub 6)(super 3+) at hydroxyl- and carboxylic-acid-terminated SAMs on a mercury electrode. Experimental evidence for voltage-induced gating of these monolayers is obtained in the form of a chronoamperometric spike, suggesting a disordering and partial desorption of the monolayer.

The structure of dolomite, CaMg[(C[O.sub.3]).sub.2], was determined from 298 to 1466 K at a constant pressure of about 3 GPa using in situ synchrotron X-ray diffraction data to investigate the state of disorder. An order parameter s, defined as 2 [x.sub.Ca] - 1, varies from s = 1 (where [x.sub.Ca] = 1) for a completely ordered dolomite to s = 0 (where [x.sub.Ca] = 0.5) for a completely disordered dolomite. On heating, there is no measured change in s until the temperature is high enough to cause exchange of [Ca.sup.2+] and [Mg.sup.2+] cations. Significant disorder began to occur at about 1234 K [s = 0.83(1)] and increases along a smooth pathway to T = 1466 K [s = 0.12(5)]. The R[bar.3] [left and right arrow] R[bar.3]c transition in dolomite is described by a modified Bragg-Williams thermodynamic model with the following molar free energy of disorder, [[bar.G].sub.d] (T; s) = R[T.sub.c][1 - [s.sup.2] + 1/2 a([s.sup.4] - 1) - (T/[T.sub.c]) {2 ln2 - (1+s)ln(1 + s) - (1 - s) ln(1 - s)}]. Using [T.sub.c] = 1466 K and a = -0.29, this model provides an excellent agreement with experimental data. Moreover, the maximum enthalpy of disorder, [[bar.H].sub.d](s = 0) = R[T.sub.c](1 - 1/2 a) ~ 14 kJ/mol, agrees with published calorimetric data. A thermodynamic description of the aragonite + magnesite [left and right arrow] dolomite reaction boundary is also presented and it reproduces the main qualitative features correctly.

The polarizable valence state potential energy curve (pVS-PEC) is derived through the systematic improvement of the valence state potential energy curve (VS-PEC) and is given as U(R) = -[(K1/R) + (K2/R (super 4)) + (K3/R (super 7)) + T/R exp (-Lambda R). The potential is tested on a broad variety of homonuclear diatoms and heteronuclear halides and hydrides.

The theory of solvatochromism based on a dielectric continuum description of the solvent and the classical Onsager cavity model was investigated and was extended to include the effect of an added 1:1 salt. The equations differed markedly for salt-free case, from several others reported in the literature dealing with the pure solvent effect and the discrepancy was clarified.

Polarized-ion models—with and without dipole reaction fields and charge-quadrupole interaction—are evaluated in calculating atomization energies, bond angles, and bending force constants of groups 2 and 12 dihalides. A study of the sensitivity to changes in the input parameters reveals a strong dependence on dipole polarizabilities. The charge–quadrupole bending terms of a multipole expansion are important for quasi-linear molecules, where the preceding terms in the expansion tend to cancel each other. They normally stabilize the linear geometry, but enhance bent structures, if a certain criterion for the ratio of quadrupole polarizabilities of metal and halide ions is fulfilled. The models explain the bent alkaline earth halides, but fail spectacularly for the group 12 halides—HgBr[sub 2] and HgI[sub 2] are even calculated as unstable relative to the constituent atoms. The unexpected weakness of ionic bonds is related to the large increase of the ionization energies by relativistic effects and the lanthanide contraction. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A thermodynamic treatment of the polarizable metal/electrolyte interface is presented and generalizes the classical electro-capillary equation, which interrelates variations in interfacial tension, cell potential, and solution composition, to include temperature changes. The result can be used in investigations of the structure of electrified interfaces; for example, in the calculation of entropy changes which occur in the solvent layer adjacent to the metal surface (inner or Stern layer) and, in particular, in the study of phase transitions in insoluble organic monolayers adsorbed at an electrochemical interface. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]