Hydration free energy sensitivity

The second term of Eq. (8.22) is smaller than the first, and is only logarithmically sensitive to the size of the solute. Equation (8.22) therefore says physically that the hydration free energy may be lowered by decreasing the density or the temperature of the solvent, the Tp factor, or by enhancing the ability of the solvent to open cavities of a size necessary to accommodate the solute, the factor in the first term. 

The PMF for Li+ adsorption shows two solvent-induced local minima. In bulk solution, the hydration shell of Li+ forms a rather rigid octahedral complex. Li+ and the water molecules in its hydration shell move cooperatively. Consequently, the hydration complex is sensitive to the barriers formed by the two pronounced layers of water molecules around z = —6k. and z = —3 A. This leads to a local free energy minimum on the solution side of each of the two maxima in the oxygen density profiles. There, molecules from the water layers can be part of the hydration eomplex (see below). 

Availability of the most efficient mechanism for achieving function in an aqueous environment. Comparison of the electrostatic charge-charge repulsion mechanism for chemo-mechanical transduction with that of the apolar-polar repulsive free energy of hydration, AG, shows the latter to be more than an order of magnitude more efficient. This becomes particularly relevant to biomedical applications of controlled release as required in drug delivery, but also whenever a sensitive and responsive (smart) biomaterial is desired. 

Here is a solvated ion, e is an electrom, and n represents the ion state of charge. The electrons, liberated by the oxidation, must flow through the material M to be consumed in an appropriate cathodic reaction. Beyond a solubility limit, precipitates of hydroxide or hydrated oxide are formed, and this surface film can provide a barrier to further dissolution. In fact, there are two film formation mechanisms the dissolution-precipitation mechattism addressed before and also the solid-state oxidation proeess M + H2O MO + 2H+ + 2e. Some films are termed passive, for stainless steels or aluminum alloys, for instance. These films can play an important role in environment-sensitive erack mitiation and fracture. Under thermodynamic equilibrium conditions, the film stability may be inferred from E =y(pH) diagrams, where E is the electrical potential related to the chemical free energy G by G = -nEF, and F is Faraday s ntrmber. At eqirilibrium, one can define the electrode potential (related to AG) and the eurrent density 1(1 ... 

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