Aqueous-phase solvation water adsorption

In a multiphase formulation, such as an oil-in-water emulsion, preservative molecules will distribute themselves in an unstable equilibrium between the bulk aqueous phase and (i) the oil phase by partition, (ii) the surfactant micelles by solubilization, (iii) polymeric suspending agents and other solutes by competitive displacement of water of solvation, (iv) particulate and container surfaces by adsorption and, (v) any microorganisms present. Generally, the overall preservative efficiency can be related to the small proportion of preservative molecules remaining unbound in the bulk aqueous phase, although as this becomes depleted some slow re-equilibration between the components can be anticipated. The loss of neutral molecules into oil and micellar phases may be favoured over ionized species, although considerable variation in distribution is found between different systems. 

Entropy-related adsorption, known as hydrophobic sorption, involves the partitioning of nonpolar organics from a polar aqueous phase onto hydrophobic surfaces, where they are retained by dispersion forces. The major feature of hydrophobic sorption is the weak interaction between the solute and the solvent. The entropy change is due largely to the destruction of the cavity occupied by the solute in the solvent and the destruction of the structured water shell surrounding the solvated organic. 

The H entry into a metal fiom an aqueous electrolyte is believed to involve the same surface-bulk transfer step as in the gas phase, but the preliminary adsorption step is a more complex process because more H sources are involved in aqueous solution, allowing more possible H surface reactions, and also because of the specificity of the electrolyte-metal interface. Whereas H adsorption in the gas phase occurs by dissociative adsorption of gaseous H2 on the free sites of a bare metallic surface, H adsorption in aqueous solution may occur either chemically by dissociation of dissolved H2 or electrochemically from solvated (hydrated) protons or water molecules it takes place on a hydrated surface and thus implies the displacement of adsorbed water molecules or specifically adsorbed ions and local reorganization of the double layer [20] competition with the adsorption of oxygen species formed from the dissociation of water may also occur [21-23], The adsorbed H layer is also in interaction with surrounding water molecules, i.e., it is hydrated [8c,24,25],... 

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