Fluorohectorite

Smectites are 2 1 charged layered silicates from natural (montmorillonite, hectorite, beidellite, saponite etc.) or synthetic (synthetic fluorohectorites, such as... 

But the same 1, 1-diphenylethylene when reacted in the presence of fluorohectorite gives oxidized products, 1, 1-diphenylethane and benzophenone. 

Due to its high charge density and homogenous layer charge distribution synthetic fluorohectorite is one of the few available clays suitable for PCH formation. However, even this clay proved to have some disadvantages. Synthetic fluorohectorite is obtained from molten fluxes and is unstable with respect to calcination (partial defluorination) at 350 °C. 

A brief comparison between fluorohectorite PCH and saponite PCH is made in Table 2 showing the structural similarities of the two mesostructured clays. 

Figure 4. Si magic angle spinning high resolution NMR spectra (79.41 MHz) for uncalcined (25 C) and calcined (350 C) Al13 pillared fluorohectorite. (Reprinted from ref. 22. Copyright 1985 American Chemical Society.)...

Vaia et al. [12] have observed that the kinetics of intercalation even under quiescent conditions (absence of external shear) are quite rapid. Using in-situ XRD (which monitors the angular shift and integrated intensity of the silicate reflections, Fig. 9) they studied the intercalation kinetics of model polymers (mono-disperse polystyrene) in organically modified fluorohectorite. 

Figure 9 shows a typical temporal series XRD patterns, for a polystyrene Mw= 30,000 (PS30)/octadecyl-ammonium modified fluorohectorite (C18FH) mixture annealed in-situ at 160 °C in vacuum. Details regarding the data collection and analysis are presented in reference [ 12]. The width of the original unintercalated peak and the final intercalated peak appear to be similar, suggesting that the polystyrene melt intercalation does not drastically alter the coherence length or disrupt the layer structure of the silicate crystallites. 

Fig. 13.Temperature dependence of 2H NMR spectra, for bulk PEO and for PEO intercalated in Li+ fluorohectorite. Adopted from [13].

Using Eq. 1.2 the time correlation function of the end-to-end vector was calculated for the hexamer systems in slits of the same thickness as the interlayer gallery of PEO/fluorohectorite intercalated hybrids [38d Section 2.2], for the whole film (Fig. 14a) and for the adsorbed chains (Fig. 14b). The film as a whole exhibits a multimodal relaxation, including fast relaxing and much slower relaxing species. The fast, bulk-like, relaxation is due to the free chains and the slower part is due to the superposition of the slower modes of the adsorbed chains and the relaxation times involved for each mode depend on the number of adsorbed segments (Fig. 15). 

Galameau et al. [81] used a similar approach to design porous clay heterostructures. They intercalated layered fluorohectorite by CjgTMA cations followed by treatment in a solution of neutral amine and TEOS, then drying and calcination. In brief, the authors proposed that the interlayer galleries of the intercalated clay are further swollen by the amine followed by insertion of TEOS, formation of rod-like micelles and silica polymerization. 

Figure 16.24 shows the schematic representation of dispersed clay particles in a polymer matrix. Conventionally dispersed clay has aggregated layers in face-to-face form. Intercalated clay composites have one or more layers of polymer inserted into the clay host gallery. Exfoliated polymer/clay nanocomposites have low clay content (lower than intercalated clay composites which have clay content -50%). It was found that 1 wt% exfoliated clay such as hectorite, montmorillonite, or fluorohectorite increases the tensile modulus of epoxy resin by 50-65%. ... 

A rather different behaviour is observed [32] for modified montmorillonite, possessing more labile and disordered structure as compared with fluorohectorite and vermiculite. 

Fig. 33. Comparison of 2H NMR line shapes for bulk d-PEO and Li-fluorohectorite-interca-lated d-PEO as a function of temperature...

The enhancement in catalytic activity of cations such as Zn(II) which has been achieved both through ion exchange as well as deposition of Zn(II) salts onto clay surfaces led to studies of the acidity and catalytic activity of such ions when incorporated directly into the lattice sites of synthetic clay minerals. Luca et al. showed that Lewis acid sites are generated on Zn2+-substituted fluoro-hectorite.27 The Zn2+-substituted fluorohectorite was synthesised by a sol-gel route. The sol was allowed to crystallise in a Parr autoclave at 250 °C for 24 hours. The Lewis acid sites were identified as Zn2+ at the edges of the fluorohectorite crystallites and were active towards the Friedel-Crafts alkylation of benzene with benzyl chloride. 

Pinnavaia [31] showed similarly that fully occupied silicate layers do not eliminate the possibility of reaction of the AI13 cation with the clay layers. A synthetic fluorohectorite is found to be pillared by AI13, and, more importantly, it is apparent from the Si and Al spectra that structural rearrangements do occur for a clay that has Si fully occupying the silicate layer. Thus Si-O-Al linkages are formed between the cation and the silicate sheet (Fig. 6). 

FIGURE 12.7 Temperature dependence of o-Ps (a) lifetime and (b) intensity for organically modified fluorohectorite (o), polystyrene ( ), and 25 wt%/75 wt% polystyrene/organicaUy modified fluorohectorite nanocomposite ( ). The solid line in (a) indicates the weight-average sum of the o-Ps lifetime values of the fluorohectorite and the polystyrene. (Adapted from Olson et al. [1997].)... 

FrOlich et al. [ 140] investigated a system in which DGEBA was mixed with hydroxy-terminated poly(propylene oxide-block-ethylene oxide) as the rubber, with the nanoclay being a synthetic fluorohectorite treated with bis (2-hydroxyethyl) methyl tallow alkylammonium ions. The clay was first blended with rubber, before being dispersed into the reactive epoxy mixture. Modification of the rubber allowed variation in miscibility and differing morphologies and properties. If the rubber was miscible, the intercalated clay led to improved toughness. If the rubber is sufficiently modified, such as with... 

Since the initial absorption (i.e. color) of the nanocomposite increases with montmorillonite addition, future investigations should focus on examining synthetic aluminosilicates that do not contain isomorphic substitution from transition metals such as Fe. Alternative types of inorganic fillers include laponite, fluorohectorite or synthetic silicic acids (31). Note that the UV exposure is not only an on-orbit concern, but will drastically affect life-cycle and long-term environment stability and performance of nanocomposites used in external terrestrial environments. 

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