Icelike structure

FIG. 26 Optimized structure of a water monolayer on mica obtained from molecular dynamic simulations by Odelius et al. The water molecules and the first layer of sihca tetrahedra of the mica substrate are shown in a side view in the top. K ions are the large dark balls. The bottom drawing shows a top view of the water. Oxygen atoms are dark, hydrogen atoms light. Notice the ordered icelike structure and the absence of free OH groups. All the H atoms in the water are involved in a hydrogen bond to another water molecule or to the mica substrate. (From Ref. 73.)... 

The history of the observation of anomalous voltammetry is reviewed and an experimental consensus on the relation between the anomalous behavior and the conditions of measurement (e.g., surface preparation, electrolyte composition) is presented. The behavior is anomalous in the sense that features appear in the voltammetry of well-ordered Pt(lll) surfaces that had never before been observed on any other type of Ft surface, and these features are not easily understood in terms of current theory of electrode processes. A number of possible interpretations for the anomalous features are discussed. A new model for the processes is presented which is based on the observation of long-period icelike structures in the low temperature states of water on metals, including Pt(lll). It is shown that this model can account for the extreme structure sensitivity of the anomalous behavior, and shows that the most probable explanation of the anomalous behavior is based on capacitive processes involving ordered phases in the double-layer, i.e., no new chemistry is required. 

The underlying metal lattice structure also has a significant effect on the water structure. As pointed out by Spohr," although the Pt-Pt nearest-neighbor distance is ao/ Jl = 0.277 nm, which is very close to the 0-0 distance in ice, the cubic symmetry of the 100 surface is incompatible with the hexagonal symmetry of the ice lattice. As a result, the water molecules cannot form a uniform monolayer and occupy all adsorption sites. On the other hand, Berkowitz and co-workers showed that the hexagonal Pt (111) surface is able to support a more complete layer of adsorbed water molecules, and one can identify patches of an icelike structure in the first layer. This freezing is further enhanced by an external electric field, as will be discussed later. 

Clarke, N.S. Hall, P.G. (1992) Adsorption of water vapour by iron oxides. 3. Inelastic incoherent neutron scattering from water adsorbed on magnetite Evidence for an icelike structure. Langmuir 8 645-649... 

A simple model that illustrated the behavior of the polarization when the water molecules are organized in water layers between perfectly flat surfaces was previously suggested.13 That model took into account the nearest-neighbor dipole interactions, but ignored the surface charges and the electrolyte ions. The model is extended here to cases in which an electrolyte as well as surface charges are also present. It will be shown that a treatment of all electrostatic interactions, in the assumption of an icelike structuring of water near interfaces, can predict an oscillatory behavior for both the polarization and the electric potential as well as a nonproportionality between the polarization and the electric fields. 

II.E.4. Evaluation of the Local Field. For a tetrahedral coordination of the water molecules, the distance between the two planar sublayers of the same layer of icelike structure is (1/3)/, l being the distance between the centers of two adjacent water molecules, while the distance between the centers of two adjacent layers is A = (4/3)l. The vertexes of the tetrahedron formed by the four first neighbors of a water molecule have the length zV8/3, while the planar projection of the tilted hexagonal lattice has the side zV8/9. The volume occupied in this structure by a water molecule is v = (8/3 3)Z8. 

For an icelike structure of water, the values of the coefficients are5 6... 

It should be emphasized that the assumption of an icelike structure of water in the vicinity of the surface is only an approximation used to calculate the dipole correlation length A, (Eq. (TO)). In feet, if the water would be organized in perfect ice-like layers parallel to the planar surface, the model would predict an oscillatory behaviour of the polarization in the vicinity of the surface [35],... 

Now, ice has a dielectric dispersion over the range 10 -10 Hz, and water over the range 10 Hz-10 Hz. Thus, the high rate of fall of dielectric constant with increased concentration for linear polyelectrolytes may come from the icelike structure of water in their vicinity. 

It has been suggested that water in biological systems has a different structure from that of free water. Thus, Szent-Gyorgyi (the discoverer of vitamin C) was the first to suggest that an icelike structure surrounded proteins and other biomolecules. Cope examined cell hydration and asked whether water is affected by conformational... 

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