Bulk-phase water structural influence

Salts, ions, and ionic liquids in water are widely studied in AIMD. Several anions [165-172], cations [153, 165, 173-182], and ion pairs [164, 183, 184], as weU as ionic hquids ion pairs [185] in water were studied using AIMD. In all cases structural as well as dynamical properties of the ion s hydration shell were examined. In some cases the influence of the solvated ions on the water molecules were studied within the Wannier approach. In general, little effect of the halogen ions on the dipole moments of the water molecules in the first hydration shell was observed, while further water molecules remain unaffected. In contrast to this, it was observed that cations increase the dipole moments of the first hydration shell water by approximately 0.2-0.5 D. The second hydration shell and the bulk phase water molecules were mostly unaffected with regard to the dipole moment by the cations as well [91]. 

The influence of an ion in an aqueous electrolyte solution on the structure of liquid water can be pictured spatially as a localized perturbation of the tetrahedral configuration shown in Fig. 2.2. In the region of the liquid nearest the ion the water molecules are dominated by SagiZ ectro-stricted mass called the primary solvation shell. In the next outer region, the water molecules intefaCT v ldy with the ion and form a structure known as the secondary solvation shell or second-zone structure. Beyond the second zone, the structure of the liquid is indistinguishable from that in the pure bulk phase. 

Originally it was stated that the influence of ions on macromolecules properties was connected with structuring or breaking of bulk water structure. However recent studies have demonstrated that either direct ion-macromolecule interactions or interactions with water molecules in the first hydration shell of the macromolecules govern the Hofmeister effect as well as phase separation in ATP systems (Zhang Cremer, 2006). Thus, in ATPS... 

Lattice models for bulk mixtures have mostly been designed to describe features which are characteristic of systems with low amphiphile content. In particular, models for ternary oil/water/amphiphile systems are challenged to reproduce the reduction of the interfacial tension between water and oil in the presence of amphiphiles, and the existence of a structured disordered phase (a microemulsion) which coexists with an oil-rich and a water-rich phase. We recall that a structured phase is one in which correlation functions show oscillating behavior. Ordered lamellar phases have also been studied, but they are much more influenced by lattice artefacts here than in the case of the chain models. 

No dependence of F relaxation time on adsorbed water was observed for concentrated fluorine-doped aluminas (- 12 wt. % F). Since the bulk structure of the solids is known to be unaffected by adsorbed water, the effect of physically adsorbed water on the F relaxation time is a surface phase effect. There are several mechanisms of relaxation by which it is possible to explain the influence of adsorbed water in a qualitative manner ... 

NOJ > J" > SCN". The reason can be understood by our experiments with the influence of ions on the water content in organic systems of two phases organic/ aqueous (Chapter lie.). The structure breaking ions increase the water content and imply an increase of the bulk water like H20 molecules which can solve ions (Chapter lie.). 

Most single-chain surfactants do not sufficiently lower the oil-water interfacial tension to form MEs, nor are they of the right molecular structure (i.e., HLB) to act as cosolvents. To overcome such a barrier, cosurfactant/cosolvent molecules are added to further lower the interfacial tension between oil and water, fluidize the hydrocarbon region of the interfacial film, and influence the curvature of the film. Typically small molecules (C3-C8) with a polar head (hydroxyl or amine) group that can diffuse between the bulk oil and water phase and the interfacial film are suitable candidates [11],... 

Water, sodium ion, and hydroxide ion concentrations have been measured within the membrane phase as a function of bulk caustic solution concentration and temperature. These internal membrane concentrations are important because of their influence on the membrane polymer morphology, structural memory, plasticity and the resultant effects on its internal resistance, viscoelasticity and material transport. In addition, the self-diffusion coefficient of the sodium ions in various Nafion membranes has been measured as a function of temperature and external caustic concentration... 

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