Montmorillonite clay plates

Figure 10.5 Schematic illustration of the use of wide angle x-ray diffraction for studying the dispersion of montmorillonite clay plates, (a) sodium form, (b) quaternary ammonium form and (c) quaternary ammonium form dispersed in polymer...

Moleculady mixed composites of montmorillonite clay and polyimide which have a higher resistance to gas permeation and a lower coefficient of thermal expansion than ordinary polyimides have been produced (60). These polyimide hybrids were synthesized using montmorillonite intercalated with the ammonium salt of dodecylamine. When polymerized in the presence of dimethyl acetamide and polyamic acid, the resulting dispersion was cast onto glass plates and cured. The cured films were as transparent as polyimide. 

The first indication of a possible connection between geological processes occurring at the boundaries between tectonic plates of the mid-oceanic ridges and the biogenesis problem was provided by J. B. Corliss (1981). He considered the hydrothermal conditions to be ideal reactors for abiotic synthesis these ideal conditions were the water temperature gradients, the pH, and the concentrations of solutes in the hot springs. The presence of certain minerals which could act as catalysts, such as montmorillonite, clay minerals, iron oxide, sulphides etc., was also very important. The initial model presented for the hydrothermal synthesis of biomolecules (Corliss, 1981) was modified, particularly by Russell (1989) and Wachtershauser (see Sect. 7.3). 

Nanofillers. Nanofillers are extremely fine particles, under a micron in size. The most successful ones have been made by intercalating quaternary ammonium surfactants between the layers of montmorillonite clay, followed by fluid polymer, to exfoliate them down to 1-nm platelets with aspect ratio of 1000/1. When these are dispersed in nylon at low concentrations of 2 to 10 percent, the tremendous numbers of plate-like particles can produce easy processing, high modulus and strength, heat deflection temperature, trans-... 

The materials of most interest are made up of alumino-silicate layers which are imperfect and so carry a negative charge, neutralised by various cations, usually sodium and calcium, intercalated between them. The layers themselves are nano-sized in thickness, with the other two dimensions being such that plates of aspect ratio in the range 50-1,000 can be obtained, without the other dimensions being so large as to pose problems. Montmorillonite clay, with a plate thickness of about 1 nm, is particularly useful. 

Adsorption isotherms of NaDS on montmorillonite and HDP-montmorillonite are shown in Fig. 13. Adsorption of the anionic surfactant via electrostatic interactions can take place only at the broken edges of the clay plates with pH-dependent surface charge sites under appropriate pH conditions. In our experiments the pH of the suspension was not adjusted, but it can be supposed that the edge sites are partly positively (A/-OH) and pardy negatively (Si-OH) charged at neutral pH. The adsorption of DS may... 

One of the biggest mistakes made in conceptualizing polymer nanocomposites is in the relative sizes of the polymer and clay plates. It is common to see schematic representations of wavy polymer molecules that are much longer than the clay plates. This picture is quite misleading and can lead to incorrect interpretation of data. In fact, the normal commercially available montmorillonite has a long dimension in the... 

The last method of surface treatment is the use of coupling agents. Unfortunately for montmorillonite, the majority of reactive hydroxides are at the edges of the clay plates. In normal commercially available montmorillonite, these edges account for only about 2% of the total surface area and therefore would not be expected to contribute greatly to the ultimate engineering properties of the composite. This point of view overlooks the fact that the edges are the first part of a clay tactoid that a polymer encounters and therefore can act as a barrier to polymer intercalation, since most polymers do not associate well with hydroxides. 

As discussed in the previous chapter concerning the structure of smectite clays, it was pointed out that these clays are turbostatic and have WAX patterns that only exhibit 001 or hkO reflections with no hkl reflections. The hkO reflections are invariant and can be used to confirm the presence of the clay in a composite at any level of exfoliation. The 001 reflections are a result of the basal spacing between the clay plates as stacks in tactoids. These peaks are highly variable and are dependent upon a number of variables, including level of exfoliation, intercalate type, and level of order. Figure 3.1 illustrates these two types of reflection for montmorillonite intercalated with dodecylpyrrolidone surface treatment where the peak at approximately 20° two theta is of the hkO type and the peaks at 2.58, 5.26, and 7.84 are of the 001 type. The three peaks are related, being the 001, 002, and 003 reflections. 

The Li ions were introduced in two different ways either before or after Zr intercalation. The montmorillonite (Weston L-Eccagun) was first exchanged with NaCl (IN) and washed. Two montmorillonites with reduced charge were prepared following the Brindley and Ertem method (13). Part of the Na+ montmorillonite was first saturated with LiCl (IN) and washed. The Li+ clay thus obtained and Na+ clay suspension were stirred for 24 hours at 25°C and dried on glass plate. The films were then heated at 220°C for 24 h in order to allow Li diffusion in the clay structure. Two different Li concentrations (F=0.4 and F=0.6) were used. The Na Li+ modified montmorillonite were dispersed in water acetone solution (1/1). The ZrOCla, 8H2O solution was added to the Na+Li+ montmorillonite (0.02g.l l Zr/Clay=5.CEC). The suspension was stirred with NaOH solution (0.1 N) up to a OH/Zr ratio of 0.5. The final pH of the suspension was 1.85. After two hours of reaction at 40°C the Zr pillared clay was washed up to constant conductivity of the solution, freeze-dried and calcined at different temperatures up to 700°C (Eni-02 and EIII-03). 

Montmorillonites (smectite clays) have structures resembling that of pyrophyllite but the structure is not electrically neutral. Exchangeable cations are located in interlamellar regions of the clay and, furthermore, the clay can be flocculated such that the plate-like crystals compact with parallel c-axes to give coherent layers. The smectites are then attractive materials with which to modify electrodes. 

Clay colloids provide a good example of the kinds of structures that can be formed upon flocculation. The association of plate-like clay particles is complicated by the fact that minerals such as montmorillonite, illite, and kaolinite can exhibit different surface charges at different particle surfaces. 

Corrensite, a mixed-layer mineral of the chlorite-montmorillonite type with an ordered structure, occurs at several levels within the Triassic Basin and in particular in the area of the Hassi R Mel deposit (Plate 15). Corrensite is a highly useful geothermal indicator in sediments (Porrenga 1967 Kiibler 1973)- In the area mentioned it starts to appear at a depth of 2.1 km and remains stable down to 2.3 km. The maximum temperatures reached were reconstructed on the basis of the appearance or disappearance of allevardite, kalkbergite and corrensite mixed-layer minerals (Fig. 8.2). Min-eralogical and crystallochemical analyses of mixed-layer clay minerals reveal the pro-... 

I. Shomer and U. Mingeigrin, A direct procedure for determining the number of plates in tactoids of smectites The Na/Ca montmorillonite case, Clays and Clay Minerals 26 135 (1978). 

Xu et al. heterocoagulated cationic PMMA latex particles of an estimated 150-200 nm in diameter with various clays, Montmorillonite (GelWhite GP and Cloisite Na+) and (fluoro)hectorites (Laponite RD, RDS, B, S, JS), having plate dimensions between 25 and 600 nm. No details on the stable colloidal armored structures were reported. Mass coagulation was induced in order to obtain a nanocomposite bulk material, which was further analyzed [23]. Chen et al. [24] added Ti02 and SiOi/TiOi nanoparticles with a positive surface charge at a very low pH of 0-2 to both anionic and cationic latexes based on PMMA. A bulk nanocomposite blend was analyzed. 

Example 5.4 The clay minerals are composed [46, 89] of sheets of tetrahedrally coordinated silica and sheets of octahedrally coordinated alumina or magnesia. These sheets occur stacked upon one another forming plate-like layers or particles. Montmorillonite, for example, clay occurs as relatively broad, thin platelets, typically about 0.3 pm across and about 2 nm thick. When dispersed in aqueous solutions of near-neutral pH to alkaline pH, the particles carry a net negative... 

Chem. Descrip. Propylene carbonate CAS m32-7 EINECS/ELINCS 20S 572-1 Uses Solvent, reactant, plastidzer for fibers, textiles, dyeing, plastics and resins, gas treating, aromatic hydrocarbon extraction, metal extraction, surf, coatings (paints, varnishes, adhesives, plastics, epoxies, mastics), foundry sand binder, lubricants, electrolytes, cosmetics (polar additive for montmorillonite or bentonite clay gellants) fire extinguishing compds. antifoam for antifreeze hydraulic brake fluids as plating medium... 

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