Fluorohectorite clay

At that time, Plee et al. stated that the layer reactivity is solely related to the origin of the layer charge, and only occurs in case of tetrahedrally charged smectites [58]. Later, however, Pinnavaia et al. proved that the mechanism of cross-linking was also possible for the octahedrally substituted fluorohectorite clay [57]. present in the former clay, was found to be responsible for the labiliza-tion of the Si-0 bonds of the tetrahedral layer (40). This promotes the linking between the host layers and the pillars to form Siday-O-Alpmar covalent bonds by an inversion of the Si04-tetrahedrons. This mechanism of cross-linking for fluorohectorite is represented in Fig. 14. 

Figure 24.11 Variation in permeability of oxygen gas through 70 30 NR/XSBR latex membranes towards different fillers (2.5 phr) at 1 bar E, F, C and Si represent sodium bentonite, sodium fluorohectorite, clay and silica, respectively. ...

Ozkan D, Kerman K, Meric B, Kara P, Demirkan H, Polveiejan M, Pinnavaia TJ, Ozsoz M (2002) Heterostructured fluorohectorite clay as an electrochemical sensor for the detection of 2,4-dichlorophenol and the herbicide 2,4-D. Chem Mater 14 1755-1761... 

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. 

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%. ... 

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). 

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... 

Powder x-ray diffraction of (a) 1-tetradecylammonium-modified fluorohectorite, (b) the organoclay after intercalation of catalyst VI, (c) after exposure of the clay-supported catalyst to ethylene for 135 min, and (d) after exposure to ethylene for 24 h. (Reproduced from Bergman, J.S. et al., Chem. Commun., 2179,1999. With permission from The Royal Society of Chemistry.)... 

Ganter et al. [62], utUized a synthetic layered fluorohec-torite silicate and organomontmorillonite to evaluate the role of functional rubber exchanged onto the synthetic clay in the preparation of styrene-butadiene rubber nanocomposites. The functional rubber that was exchanged onto the fluorohectorite was amino-terminated polybutadiene. The styrene-butadiene was dispersed in solvent and then dis-... 

Varghese et al. [79,80], observed that pure, synthetic sodium fluorohectorite does not disperse well into natural mbber. However, when polyurethane mbber was dispersed with the clay and namral mbber, excellent mechanical properties were observed when the clay was present at 10 wt%. The clay preferred to be associated with the urethane dispersed phase. 

Varghese et al. [81-84] evaluated pure montmorillonite, kaolin, and synthetic fluorohectorite by mixing an aqueous dispersion of clay, an aqueous dispersion of natural latex. 

When NR was the rubber, a NR latex was mixed with Na-bentonite and Na-fluorohectorite, varying the concentration of clays from 1 to 2.5 phr and determining rheological properties with a coaxial cylinder viscometer. Viscosity increased with clay loading. Pseudo solid-like behaviour was observed in bentonite-filled composites at the loading of 2.5 phr, whereas a behaviour close to that of the Newtonian fluid was shown by unfilled NR. Stronger rubber bentonite interaction was revealed by the higher viscosity, the lower power-law indexes and the slope of the Kraus plot. ... 

Clays and layered silicates Montmorillonite, hectorite, saponite, fluoromica, fluorohectorite, vermiculite, kaolinite, magadite... 

By applying AIA techniques analogous to those discussed in Section 23.5.1, the aspect ratio of the clay particles in a rubber matrix can be determined.For example, the high aspect ratio of stacked and distorted fluorohectorite layers was observed in TEM micrographs and was correlated with the reinforcing effect brought about by this silicate. 

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