Intercalated hectorite, interlayer

Layers of silicate-bearing hectorites were expanded by the intercalation of the lengthwise alkyl quaternary ammonium cation and simultaneously the interlayer anisotropic silicates stood normally to the layer. 

A series of cluster complexes has been intercalated into hectorite, again with P-P+ as the cationic ligand. Typical is the formation of 1t4(CO)9(P-P+)3 within the clay. Intercalation of the clusters within the clay causes an increase in the interlayer spacing to as large as 17.5 A. 

Kurokawa et al. [258-260] developed a novel but somewhat complex procedure for the preparation of PP/clay nanocomposites and studied some factors controlling mechanical properties of PP/clay mineral nanocomposites. This method consisted of the following three steps (1) a small amount of polymerizing polar monomer, diacetone acrylamide, was intercalated between clay mineral [hydrophobic hectorite (HC) and hydrophobic MMT clay] layers, surface of which was ion exchanged with quaternary ammonium cations, and then polymerized to expand the interlayer distance (2) polar maleic acid-grafted PP (m-PP), in addition was intercalated into the interlayer space to make a composite (master batch, MB) (3) the prepared MB was finally mixed with a conventional PP by melt twin-screw extrusion at 180°C and at a mixing rate of 160 rpm to prepare nanocomposite. Authors observed that the properties of the nanocomposite strongly dependent on the stiffness of clay mineral layer. Similar improvement of mechanical properties of the PP/clay/m-PP nanocomposites was observed by other researchers [50,261]. 

Under the appropriate conditions, monomers occupy virtually the entire space of pores or the whole interlayer space. Subsequent oxidative polymerization was carried out in the presence of molecular oxygen (as an electron acceptor) and a redox-active host that catalyzes electron transfer. Layered silicates containing metal ions are of particular interest because they initiate polymerization of an intercalated monomer. Thus when Na ions in hectorite are replaced by Cu or Fe, styrene can be polymerized both in the pores and on the smface. The polymer has a brushlike structure, which indicates that the inorganic smface possesses an orienting effect. This effect decreases as the chain grows away from the smface. 

When PEO is intercalated from acetonitrile solutions into montmorillonite and hectorite (122,124-126), the resulting nanocomposites present characteristics that depend on the nature of the interlayer cation in a similar way to that observed for intercalation of crown ethers into smectites (44,46,49,127,128). Such behavior implies the existence of ion-dipole interactions between the oxygen atoms of the polymer and certain interlayer cations, as occurs for PEO-salt complexes (129). The fact that the synthesis is carried out in nonaqueous solutions determines that the polymer may replace the hydration shell usually accompanying the interlayer cations, as shown by IR spectroscopy (124). The effectiveness of such a process is related to the hydration energy of the cation. When this energy is high (calcium... 

Smectite clay minerals, such as montmorillonite, saponite, nontronite, hectorite, stevensite, vermiculite and haloysite have been known to act as hosts of intercalated compounds [7] and to function as catalysts for various organic reactions [8]. The properties of smectites depend upon the interlayer cations [9], which are easily exchangable for inorganic or organic cations. 

The effect of intercalating various alkylammonium cations into the hectorite host is to increase the interlayer spacing of the Na-form (2.8 A when partially hydrated) to 4.2, 4.9, and 5.5 A, when TMA, TPrA, and TPeA ions are intercalated. 

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