Ice, structure

Chapter 9, on entropy and molecular rotation in crystals and liquids, is concerned mostly with statistical mechanics rather than quantum mechanics, but the two appear together in SP 74. Chapter 9 contains one of Pauling s most celebrated papers, SP 73, in which he explains the experimentally measured zero-point entropy of ice as due to water-molecule orientation disorder in the tetrahedrally H-bonded ice structure with asymmetric hydrogen bonds (in which the bonding proton is not at the center of the bond). This concept has proven fully valid, and the disorder phenomenon is now known to affect greatly the physical properties of ice via the... 

Number and geometry of foreign particles, which influence the heterogeneous nucle-ation the more their structure is similar to the ice structure, the better is their effectiveness as nuclei. 

Nunner [ 1.104] photographed with a special cryomicroscope the change of the planar front of a 0.9 ck NaCl solution during directional freezing in 360 s to a stable dendritic ice structure (Fig. 1.37). The concentrated NaCl (dark border) ean be seen on the surface of the ice crystals. 

Liou, Y. C., Tocilj, A., Davies, P. L., andjia, Z. (2000). Mimicry of ice structure by surface hydroxyls and water of a beta-helix antifreeze protein. Nature 406, 322-324. 

ESR spectroscopy can be used with adsorbed paramagnetic ions to study the liquid associated with mineral surfaces. Cu(II) and Mn(II) have been used in his type of investigation, although difficulties are encountered with observing a resonance from Mn(II) in distorted environments. Measurements of Cu(II) on silica at room temperature and above have shown that adsorbed water behaves in the same manner as bulk water, but at lower temperatures it experiences a decreased mobility (61). On freezing two types of water are found one which is freezable and undergoes crystallization and the other which is unfreezable, in which the ice structure cannot be formed because of the surface interaction. NMR, IR and differential thermal... 

Figure 5.1 Hexagonal ice structure showing open, tetrahedrally coordinated structure...

O Neil and Truesdell (1991) have introduced the concept of structure-making and structure-breaking solutes structure makers yield more positive isotope fractionations relative to pure water whereas structure breakers produce negative isotope fractionations. Any solute that results in a positive isotope fractionation is one that causes the solution to be more structured as is the case for ice structure, when compared to solutes that lead to less structured forms, in which cation - H2O bonds are weaker than H2O - H2O bonds. 

Figure 2.52. (a) The bilayer ice structure on metal surfaces. Dark and grey spheres represent atoms. Half of the water molecules bind directly through the oxygen to the surface metal atoms. The remaining molecules are displaced toward the vacuum in the H-up configuration, (b) The flat ice structure on metal surfaces with atoms in Pt— and Pt—HO bonding water molecules, respectively. From Ref. [106]. 

The simplest as well as the most complete hydrogen-bonded structures are those formed by water molecules in ice. The simplicity, however, is only of the first order. The ice structure, even in regard to the regular or irregular arrangement of the water molecules, is one of extreme complexity of which we shall hear later in this discussion. 

Mixture Models Broken-Down Ice Structures. Historically, the mixture models have received considerably more attention than the uniformist, average models. Somewhat arbitrarily, we divide these as follows (1) broken-down ice lattice models (i.e., ice-like structural units in equilibrium with monomers) (2) cluster models (clusters in equilibrium with monomers) (3) models based on clathrate-like cages (again in equilibrium with monomers). In each case, it is understood that at least two species of water exist—namely, a bulky species representing some... 

We have also begun a study of the aluminum slab in water using the water model described in Ref. 35. We have introduced 180 water molecules into the simulation cell in an ice structure and have allowed them to thermally equil-brate to 300 K with the electronic structure of the aluminum slab frozen. 

At very high pressures (in the GPa range), gas hydrates can undergo structural transitions to hydrate phases and filled ice structures. Figure 2.11 illustrates the structural changes that have been reported for gas hydrates at very high pressures at... 

The plain five membered rings of clathrates may have a lesser degree of freedom as the non-plain six membered ring of the normal ice structure. We can expect that the entropy of this structure is smaller than in the ice lattice. This model could interpret the entropy effect of aqueous mixtures without structure increase. 

Figure 6.6. The ice structure. Oxygen atoms are in P and T sites of the wurtzite structure. Both of the disordered H positions between oxygen atoms are shown.

---