Intercalation and Exfoliation

Chemically the interlayers in the modular phases described previously are relatively reactive. This has been exploited to fabricate large numbers of phases that are not available via the normal solid-state chemistry preparative method of high-temperature synthesis from mixed oxides or oxide precursors. The technique generally employs low temperatures, typically room temperature to 300°C, and long reactions times, of the order of 1 week. This procedure, termed chimie douce , is often translated as soft chemistry but is better called mild chemistry or gentle chemistry . Under such conditions, much of the stmcture remains intact, and the product phases have a strong topotactic relationship to the starting stmctures. For the modular perovskite phases, in 

Many other reactions could be illustrated, including the formation of ordered phases with n, stacking of perovskite slabs, ordered stacking of perovskite slabs and brucite-type double hydroxide layers or perovskite blocks with no interlayer cations present. For further information on the stmctural chemistry of these complex reactions, see Further Reading. 

Lichtenberg, A. Hermberger, K. Wiedenmann, Prog. Solid State Chem., 36, 253-387 (2008). 

A review of the structures and properties of cuprates, cobaltites and manganites, with much information on modular phases, is given by  

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This is a highly polar polymer and crystalline due to the presence of amide linkages. To achieve effective intercalation and exfoliation, the nanoclay has to be modified with some functional polar group. Most commonly, amino acid treatment is done for the nanoclays. Nanocomposites have been prepared using in situ polymerization [85] and melt-intercalation methods [113-117]. Crystallization behavior [118-122], mechanical [123,124], thermal, and barrier properties, and kinetic study [125,126] have been carried out. Nylon-based nanocomposites are now being produced commercially. 

Graphite materials produced at 600-1100°C may find applications in lithium batteries and supercapacitors. Currently, similar flakes are produced in a complex process including graphitization at above 2500°C,16 followed by intercalation and exfoliation of graphite15. Here we demonstrate that synthesis of graphite from iron carbide can be done in one step at moderate temperatures. 

Su, S., Jiang, D. D., and Wilkie, C. A. Novel polymerically-modified clays permit the preparation of intercalated and exfoliated nanocomposites of styrene and its copolymers by melt blending, Polym. Degrad. Stab. (2004), 83, 333-346. 

Both intercalated and exfoliated nanocomposites, containing 3-5% of nanoparticles (w/w), reportedly show better or comparable flame resistance compared with plastics filled up to 30-50% with traditional flame retardants. Another way to increase flame retardancy is to combine ATH or magnesium hydroxide with organo-clays. It was reported that organoclays and some classical flame retardants, such as brominated compounds, showed a synergism between them [13]. 

For explaining the apparent contradictory results concerning the restricted dynamics in intercalated and exfoliated PLSNs, Lu and Nutt [2003] proposed a model with three different relaxation domains and three different relaxation rates. The relaxation properties differ depending on the extent to which the iayered silicates are exfoliated, the strength of interactions between silicate layers and polymer matrices, the grafting density, and the ceramic content. The authors concluded that a system with fully exfoliated silicate dispersion and strong interactions is expected to exhibit slow relaxation behavior (high Tg), whereas a system with intercalated silicates and weak interaction should display fast relaxation dynamics (low Tg). 

Bousmina, M., Study of intercalation and exfoliation processes in polymer nanocomposites. Macromolecules, 39, 4259-4263 (2006). 

In practice, the techniques of blending, compositing and nano-reinforcement are often used together. Thermoplastic starch/poly(vinyl alcohol) (PVOH)/clay nanocomposites exhibited the intercalated and exfoliated structures [260]. Mont-morillonite (MMT) with three types of cation or modifier (Na", alkyl ammonium ion, and citric acid) was examined. The prepared nanocomposites with modified montmorillonite indicated a mechanical improvement in the properties, in comparison with pristine MMT. 

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