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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.