Layered silicate intercalation compounds

Reactions between certain solids possessing layered structures (e.g. graphite, silicates, metal dichalcogenides such as TaS2) and Lewis bases such as ammonia and pyridine, forming intercalation compounds, are discussed in the next section. 

In numerous works dealing with the combination of nanoparticles and FR compounds, surface modifications of nanoparticles were only aimed to promote good dispersion of the nanoparticles into the polymer matrix (with intercalated or exfoliated morphologies for layered silicates as nanoparticles), even in the presence of the usual FRs, for example ammonium polyphosphate (APP) or magnesium hydroxide (MH). The initial aim was to combine the individual effects of each component to achieve strong synergistic effects. 

Now the stoicheiometry of all mineral phases is complex and beset by problems of isomorphous substitution. In the sheet silicates such as talc, the incorporation of material between the layers, as occurs in intercalation compounds, is also common. Beneath this complexity, though, lies the fact that the tetrahedral-octahedral framework of these materials is of a fixed and inflexible metal to oxygen stoicheiometry. 

February 29th) into the calendar to make it match the. solar year. Most work on intercalation compounds has been on synthetic systems in which atoms, ions, or molecules have been inserted between layers of the host material. However, some aluminosilicates that we have encountered above provide useful examples. Thus talc and micas form layered structures with ions between the silicate sheets (Fig. 16.3). Some minerals, including all clays, have water molecules intercalcatcd between the framework sheets. In some, such as vermiculile, the water may rapidly and dramatically be evacuated by heating. The water molecules leave faster than they can ditfuse along the layers—exfoliation occurs. The result is the familiar expanded vermiculile used as a packing material and as a potting soil conditioner. 

The presence of cations between the slabs of numerous layered silicates allows various exchange reactions, including those involving organic cations. These types of layered silicates can be considered as intercalation compounds by themselves. 

The field of intercalation chemistry in layered silicates is huge. It includes many types of intercalates, and a large variety of host structures that can be modified before intercalation by various exchange reactions. Organoclays, for example, represent a family of compounds resulting from the introduction of organic cations by ion exchange and which also allow intercalation. 

Intercalation of poly(ethylene oxide) into a lithium-ion exchanged clay gives an interesting class of layered silicate nanocomposites that are lithium-ion electrolytes. Compounds have been prepared by intercalation from methanol/water solutions and by melt intercalation. Melt intercalation typically gives samples with higher polymer contents than the solution method and with higher lithium-ion conductivity though the conductivity is probably still too low for practical applications. 

The synthesis of polymer nanocomposites is an integral aspect of polymer nanotechnology. By inserting the nanometric inorganic compounds, the properties of polymers improve and hence this has a lot of applications depending upon the inorganic material present in the polymers. The improvements obtained in day/PP nanocomposite structure can make this commercial thermoplastic polymer more suitable for automotive, construction and packaging applications. Different alkyl ammonium surfactants and compatibilizer was used to produce layered silicate/PP nanocomposites by the same melt intercalation technique. 

Komori, Y. and Kurada, K. (2000). Layered silicate - Polymer Intercalation Compounds, In Pinnavaia, T.J. and Beal, G.W. (eds). Polymer Layered Silicate Nanocomposites, Wiley, New York. 

It has been generally assessed that the mechanism of interaction among the components of PO/day nanocomposites involves the functionalities of the functional polymer used as matrix or compatibilizer. The most frequent explanation is related to the hydrophilic/ hydrophobic balance of components involving some kind of undefined polar interaction between the silicate layers and the functional polymer (Alexandre and Dubois 2000, Sinha Ray and Okamoto 2003, Pavlidou and Papaspyrides 2008). The direct intercalation/interac-tion of a wide numbers of MAH-grafted low-molecular-weight compounds with layered silicates has been studied suggesting that the anhydride can promote the intercalation even if this is not a modeling of polymer intercalation (Sibold et al. 2007). 

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