Interlayer distance, intercalation studies

The rate constants and interlayer distances determined from X-ray diffraction patterns for the intercalation studies described above are given in Table V. In those systems where intercalation causes large changes in the interfacial potential (ZrP and TiS2), Equations 32 and 33 were modified using intrinsic rate constants. In cases where steady state reactive intermediates were postulated, the rate constants in Equations 32 and 33 were modified as shown in Table V. 

Table V. Rate Constants and Interlayer Distance in Intercalation Studies a...

Other substitution reactions lead to more crystalline phases. Reaction of (4-aminopyridine)i/4FeOCl with methanol at 100 °C, for example, gives crystalline FeOOMe. Reactions with aliphatic and aromatic alkoxides and acids, of the type shown in equations (13) and (14), have also been studied. More rigid and longer molecules, such as 4-hydroxybenzoic acid, can crosslink the iron oxide layers. An initial intercalation step that causes an expansion of the FeOCl interlayer distance is followed by a second substitntion step leading to layer crosslinking. 

Porphyrins were first introduced into clays in 1977 by the physical absorption of porphyrin molecules into montmor-illonite in aqueous solutions." The most common examples are the binding of tetracationic M(TMPyP) porphyrins, M = Co(II), Mn(III), Fe(III), into montmor-illonite clays. Co(TMPyP) was the first porphyrin to be intercalated into montmorillonite by ion exchange in acid solution. The interlayer distance expanded from 27 to 37 A upon intercalation. UV-visible studies revealed the retention of cobalt ions in the porphyrin molecules. Mansuy and coworkers have extended this approach and prepared the Mn-porphyrin intercalated materials. These solids are efficient alkene epoxidation and alkane hydroxylation catalysts." Additionally, the catalyst exhibited a marked shape selectivity in favor of small linear alkanes when compared to more bulky substrates. It was also shown that... 

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]. 

The kinetics of intercalation and deintercalation of alkali metal ions were investigated in pressure-jump experiments while monitoring the electrical conductivity of the samples (32). These studies indicate biphasic kinetics whose magnitudes are in milliseconds the rates of the fast and slow components increased with increased concentrations of the metal ions. The forward and reverse rates depend on the interlayer distances, and the fast and slow components have been attributed to the ingress of ions into the galleries and interlayer diffusion, respectively. Similar biphasic kinetics on millisecond-second time scales were also observed in pressure-jump experiments for the deprotonation-reprotonation of a-ZrP (33). In the latter case, the slow and fast components have been attributed to deprotonation from the surface and from the interlayer regions of the solid, respectively. 

The pore opening of pillared clays, which plays an important role in shape selective catalysis, is determined both by the interlayer distance and by the density of pillar or the number of pillars. The interlayer distance depends on the dimension of intercalating species. Considerable efforts have been undertaken to develop pillared clays with different interlayer distances. Indeed, pillared clays having the interlayer distance from 0.4 to 2.0 nm were prepared using various intercalating species(refs. 3-7). In contrast, there have been few studies concerning the control of pillar density or the number of pillars. 

In-situ synthesis of caprolactone in the interlayers of Cr -modified fluorohec-torite was reported by Messersmith et al. [35). The microstracture development was studied by using XRD as shown in Figure 1.17. The unintecalated filler had a basal plane spacing of 12.8 A, which was increased to 14.6 A for the intercalated filler swollen with caprolactone. After the polymerization of caprolactone in and around of filler interlayers, a final basal plane spacing of 13.7 A was observed for the nanocomposite. The observed basal plane spacing correlated well with 4-A interchain distance in the crystal structure of poly(caprolactone). 

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