Interlayer water

In the context of the structural perturbations at fluid-solid interfaces, it is interesting to investigate the viscosity of thin liquid films. Eaily work on thin-film viscosity by Deijaguin and co-workers used a blow off technique to cause a liquid film to thin. This work showed elevated viscosities for some materials [98] and thin film viscosities lower than the bulk for others [99, 100]. Some controversial issues were raised particularly regarding surface roughness and contact angles in the experiments [101-103]. Entirely different types of data on clays caused Low [104] to conclude that the viscosity of interlayer water in clays is greater than that of bulk water. 

Subsequent work showed that a modification of the synthesis procedure produced a 10A hydrate which> if dried carefully, would maintain the interlayer water in the absence of excess water (27). This material is optimal for adsorbed water studies for a number of reasons the parent clay is a well-crystallized kaolinite with a negligible layer charge, there are few if any interlayer cations, there is no interference from pore water since the amount is minimal, and the interlayer water molecules lie between uniform layers of known structure. Thus, the hydrate provides a useful model for studying the effects of a silicate surface on interlayer water. 

Characterization of Interlayer Water. X-ray diffraction studies of the 10A hydrate show no hkl reflections indicating a lack of regularity in the stacking of the kaolin layers. In addition to the 10A hydrate, two other less hydrated kaolinites were synthesized. Both have one molecule of water for each formula unit in contrast to the 10A hydrate which has two. These less hydrated clays consequently have smaller d(001) spacings of 8.4 and 8.6 A. The synthesis conditions for these two hydrates are described in (22.). By studying the interlayer water in the 8.4 and 8.6A hydrates, it was possible to formulate a model of the water in the more complicated 10A hydrate. 

Heat Capacity Measurements and Interlayer Water Structure. The heat capacity of the interlayer water has been measured for the 10A,... 

In LDHs, the layer hydroxyl groups can act as hydrogen bond donors to both the interlayer anions and the oxygen atoms of interlayer water molecules. The interlayer water molecules can also form hydrogen bonds between themselves and can act as hydrogen bond donors to the interlayer anions. A molecular dynamics study of an Mga A1 - Cl LDH has been reported by Wang et al. [223], and indicated that the interlayer species are distributed between two sublayers such that none of them is able to form direct hydrogen... 

For [LiAl2(OH)6]Cl H2O, molecular dynamics simulations suggest that the both interlayer water molecules and chloride anions are located in the middle... 

Calcination of LDHs removes the interlayer water, interlayer anions and the hydroxyl groups, resulting in a mixed metal oxide that cannot be achieved by mechanical means. It is especially interesting that the calcined LDH is able to regenerate the layered structure when it is exposed to water and an-... 

Fig. 2.14 The structure of halloysite. Hydrogen bonded interlayer water is shown in this 10 A or 0.01 nm. form.

By comparison with many other silicate minerals, isotope studies of natural clays are complicated by a number of special problems related to their small particle size and, hence, much larger specific surface area and the presence of interlayer water in certain clays. Surfaces of clays are characterized by 1 or 2 layers of adsorbed water. Savin and Epstein (1970a) demonstrated that adsorbed and interlayer water can exchange its isotopes with atmospheric water vapor in hours. Complete removal of interlayer water for analysis with the total absence of isotopic exchange between it and the hydroxyl group, may not be possible in all instances (Lawrence and Taylor 1971). 

The nature of the interfacial structure and dynamics between inorganic solids and liquids is of particular interest because of the influence it exerts on the stabilisation properties of industrially important mineral based systems. One of the most common minerals to have been exploited by the paper and ceramics industry is the clay structure of kaolinite. The behaviour of water-kaolinite systems is important since interlayer water acts as a solvent for intercalated species. Henceforth, an understanding of the factors at the atomic level that control the orientation, translation and rotation of water molecules at the mineral surface has implications for processes such as the preparation of pigment dispersions used in paper coatings. 

For the disproportionation reactions, the hydrotalcite-1 ike materials were evacuated at 453 K for 2 h before use to drive out interlayer water molecules. A 41 mmol of trimethoxysilane was added into the flask containing 0.62 g of the material (2.0 mmol of interlayer anions) under a nitrogen atmosphere. The reaction mixture was analyzed for (CH30)3SiH and (CH30)4Si by the gas chromatograph described above, using heptane as a standard. 

Figure 8.2 Topotactic dehydration of Mo03-2H20 (a) (101) projection of M0O3 2H2O (b) (001) projection of M0O3 H2O and (c) (100) projection of M0O3. Open circles denote interlayer water and filled circles, coordinated water. (After GUnter, 1972.)...

Hydrogen bonding with interlayer water (triazine is bond acceptor)... 

Hydrogen bonding with basal oxygens of aluminate tetrahedra (triazine is bond donor) Hydrogen bonding with interlayer water (triazine is bond acceptor)... 

The expanded or expandable 2 1 clay minerals vary widely in chemical composition and in layer charge. These minerals are characterized by the presence of loosely bound cations and layers of water or polar organic molecules between the silica sheets. The interlayer width is reversibly variable. The interlayer water can be driven off at temperatures between 120° and 200°C. Sodium, calcium, hydrogen, magnesium, iron, and aluminum are the most common naturally occurring interlayer cations. 

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