Montmorillonite alkylammonium

Application of thermal analysis in organoclay characterization DTA of montmorillonite/ alkylammonium Jordan (32) and Allaway (247)... 

Ogawa M, Shirai H, Kuroda K, Kato C (1992) Solid-state intercalation of naphthalene and anthracene into alkylammonium-montmorillonites. Clays Clay Miner 40 485-490... 

Theng BKG, Aislabie J, Fraser R (2001) Bioavailability of phenanthrene intercalated into an alkylammonium-montmorillonite clay. Soil Biol Biochem 33 845-848... 

Theng BKG, Greenland DJ, Quirk JP (1967) Adsorption of alkylammonium cations by montmorillonite. Clay Miner 7 1-17... 

Theng BKG, Newman RH, Whitton JS (1998) Characterization of an alkylammonium-montmorillonite-phenanthrene intercalation complex by carbon-13 nuclear magnetic resonance spectroscopy. Clay Miner 33 221-229... 

Vansant EF, Uytterhoeven JB (1972) Thermodynamics of the exchange on n-alkylammonium ions on Na-montmorillonite. Clays Clay Mineral 20 47-54... 

The inductive effect of the carbon chain in the clay phase amounts to (only) 5 to 7 % of the effect in the gas phase. Ammonium cations in the interlamellar region of clay minerals are therefore less hydrated than in equilibrium solution. The free energy of alkylammonium exchange increases with charge density from Laponite (42) < Red Hill montmorillonite (40) < Camp Berteau montmorillonite (41) in line with the smaller interlamellar hydration status of the adsorbed cation at higher charge density. 

The intercalation of alkylammonium cations in clays, specifically tetraalkylammonium, for the first time, was carried out by Barrer and MacLeod. These researchers prepared pillared materials by exchanging the alkali and alkaline earth cations present in a montmorillonite clay with tetraalkylammonium [29], Nevertheless, the obtained material was thermally unstable and, consequently, had no viable application in catalysis. 

Over the past 15-20 years, there has been a renewed and growing interest in the use of clay minerals as catalysts or catalyst supports. Most of this interest has focused on the pillaring of smectite clays, such as montmorillonite, with various types of cations, such as hydrated metal cations, alkylammonium cations and polycations, and polynuclear hydroxy metal cations (1-17). By changing the size of the cation used to separate the anionic sheets in the clay structure, molecular sieve-like materials can be made with pore sizes much larger than those of conventional zeolites. 

There are several investigations of organic cations in clays in the literature, most of which originate from the soil research area. Many studies involving NMR were done by Mortland and coworkers [51]. A recent report involving alkylammonium cations in vermiculite and montmorillonite further depicts the kinds of interactions to expect when examining interlayer species 152]. C MAS spectra show that tetramethylammonium cations are able to reorient essentially isotropically in the clays, whereas the larger hexadecyltrimethylammonium is... 

Barrer, R. M. and Dicks, L. W. R. 1967. Chemistry of soil minerals. Part IV Synthetic alkylammonium montmorillonites and hectorites. J. Chemical Society (A) 1523-29. 

Primary alkyl amines, when exposed to acidic medium, protonate the amine function resulting in the formation of alkylammonium ions. Montmorillonite exchanged with long-chain alkylammonium ions can be dispersed in polymer matrix. 

Representative snapshots of montmorillonite of high CEC (143meq/100g) with alkylammonium surfactants H3N+-C H2 +i at equilibrium distance. The formation of partially packed and densely packed alkyl monolayers, bilayers, and pseudo-trilayers can be seen. Head groups are positioned very close to the surface due to hydrogen bonds and, therefore, vertically separated between the two clay layers at equilibrium distance even for short chain length. (Reproduced from Fu, Y.T. and Heinz, H., Phil. Mag., in press.)... 

Fu, Y. T. and Heinz, H. 2010. Cleavage energy of alkylammonium-modified montmorillonite and the relation to exfoliation in nanocomposites Influence of cation density, head group stmc-ture, and chain length. Chemistry of Materials 22 1595-1605. 

Osman, M. A., Ploetze, M., and Skrabal, P. J. 2004. Structure and properties of alkylammonium monolayers self-assembled on montmorillonite platelets. Journal of Physical Chemistry B 108 2580-2588. 

The layered silicate nanoparticles are usually hydrophilic and their interactions with nonpolar polymers are not favorable. Thus, whereas hydrophilic polymers are likely to intercalate within Na-activated montmorillonite clays [24-29], hydrophobic polymers can lead to intercalated [23,30-32] or exfoliated [33] structures only with organophilized clays, i.e., with materials where the hydrated Na+ within the galleries has been replaced by proper cationic surfactants (e.g., alkylammonium) by a cation exchange reaction. The thermodynamics of intercalation or exfoliation have been discussed [34-37] in terms of both enthalpic and entropic contributions to the free energy. It has been recognized that the entropy loss because of chain confinement is compensated by the entropy gain associated with the increased conformational freedom of the surfactant tails as the interlayer distance increases with polymer intercalation [34,38], whereas the favorable enthalpic interactions are extremely critical in determining the nanocomposite structure [39]. 

At the same time Bala et al. studied the filler effects of organomodified dodecyl alkylammonium intercalated montmorillonite (12C-MNT) for natural rubber (NR) and styrene butadiene rubber (SBR). The results showed that tensile strength, modulus, and elongation at break increased significantly as compared to pure vulcanized NR and SBR when 4 wt% of 12C-MNT was used as filler. In the case of NR, these properties decreased drastically for 1 wt% of pure Na-MNT [122]. 

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