Expanded interlayer spacing

If a system with an artificially and permanently expanded interlayer space was to be modeled (in order to model an external surface, for example), all calculations were performed under NVT (constant mass, volume, and temperature) conditions. In certain other situations such as those described below, the artificially expanded systems were first allowed to equilibrate under NVT conditions and subsequently subjected to NPT (constant mass, pressure, and temperature) conditions, whereupon the separated layers spontaneously reannealed, thereby restoring the equilibrium interlayer spacing characteristic of that particular system. 

Primary amines immobilized in the acidic montmorillonite (H+-mont) interlayer space, prepared by a silane-coupling reaction using 3-aminopropyltriethoxysilane, acted as base sites together with the interlayer acid sites to promote tandem deacetalization-Knoevenagel condensation (Scheme 6.22) [134]. On the basis of CP/MAS (CP, cross-polarization) NMR results, it is proposed that a free NH2 group in an expanded interlayer space of H+-mont in the presence of heptane... 

The mechanical properties of PUCLNs have been comprehensively examined. It has been reported that a series of intercalated PUCLNs presented exceptionally mechanical enhancement in comparison with pure PU. It was reported that the strength and strain at break of pure PU can be increased by >44% and 20%, respectively, with 21.5 wt% MMT [32]. Organoclay has much stronger reinforcing effects than MMT for two reasons (i) organoclays with expanded interlayer spacing... 

These crystals have the potential to be efficient solid catalysts due to their cation-exchange abilities and to the fact that various metal cations can be easily introduced into their expandable interlayer spaces. 

Various solid materials have been used as hosts of photoactive organic molecules such as zeolties, mesoporous silicas, layered materials, etc. The advantage of layered materials to use as the host materials of photoactive organic molecules is that they possess two-dimensional and expandable interlayer space, which can accommodate a wide variety of... 

X-ray diffraction patterns yield typical 1.2—1.4 nm basal spacings for smectite partially hydrated in an ordinary laboratory atmosphere. Solvating smectite in ethylene glycol expands the spacing to 1.7 nm, and beating to 550°C collapses it to 1.0 nm. Certain micaceous clay minerals from which part of the metallic interlayer cations of the smectites has been stripped or degraded, and replaced by expand similarly. Treatment with strong solutions of... 

Micro-composites are formed when the polymer chain is unable to intercalate into the silicate layer and therefore phase separated polymer/clay composites are formed. Their properties remain the same as the conventional micro-composites as shown in Figure 2(a). Intercalated nano-composite is obtained when the polymer chain is inserted between clay layers such that the interlayer spacing is expanded, but the layers still bear a well-defined spatial relationship to each other as shown in Figure 2(b). Exfoliated nano-composites are formed when the layers of the day have been completely separated and the individual layers are distributed throughout the organic matrix as shown in Figure 2(c). 

Fig. 3. Possible arrangements of long-chain quaternary ammonium cations (here tetradecyltrimethylammonium) in the interlayer space of expanding 2 1 layer silicates. After Lagaly (1982) and Jaynes and Boyd (1991a).

The interlayer space of LDHs can be expanded to some extent in a suitable solvent medium, which favors the ion exchange process. An aqueous medium, for example, favors the exchange by inorganic anions, whilst an organic solvent favors exchange by organic anions [14]. 

In both the above cases, we have 2D processes. Following nucleation, the reaction may be either phase boimdary controlled (i.e. the rate is limited by the rate at which the interlayer space expands to accommodate the guest) or diffusion controlled (i.e. the reaction rate is controlled by the rate at which the guests diffuse between the layers - the interlayer spacing expands instantly as the guests move). 

The CEC of clay minerals is partly the result of adsorption in the interlayer space between repeating layer units. This effect is greatest in the three-layer clays. In the case of montmorillonite, the interlayer space can expand to accommodate a variety of cations and water. This causes montmorillonite to have a very high CEC and to swell when wetted. This process is reversible the removal of the water molecules causes these clays to contract. In illite, some exchangeable potassium is present in the interlayer space. Because the interlayer potassium ions are rather tightly held, the CEC of this illite is similar to that of kaolinite, which has no interlayer space. Chlorite s CEC is similar to that of kaolinite and illite because the brucite layer restricts adsorption between the three-layer sandwiches. 

Interlayer spacing expands from 10 to 14-15 A because Al3 substitutes Si4 in the tetrahedral position... 

Montmorillonite has some important characteristics that justify its use as a model substance for the study of the interfacial processes of rocks and soils. It is a dioctahedral three-layer clay (2 1 clays, TOT) an A10(0H) octahedral sheet is between two tetrahedral Si04 layers (Chapter 1, Table 1.2). The distance between the layers is not fixed (—O—O-bonds) the layers can be expanded. Because of the layered structure, it has two surface types external and internal surfaces. The external surface is the surface of the particles (edge surface), and its size depends on particle size distribution. Its area can be measured by the BET method, usually by the adsorption of nitrogen gas at the temperature of liquid nitrogen (Chapter 1, Section 1.1.3). The internal surface is the surface between the layers (interlayer surface), and its size can be determined by introducing substances into the interlayer space (e.g., water) (Chapter 1, Section 1.1.3). The internal surface area is independent of particle size distribution. 

Clay mineral Type CEC ( cmolc kg- ) Surface area (m g- ) Expanding non-expanding c spacing Interlayer nm binding ... 

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