Interlamellar domain

The term "anionic clay" is used to designate synthetic or natural lamellar hydroxides with interlayer domains containing anionic species. This designation refers to the more usual "cationic clays" whose interlamellar domains contain cationic species. The more structural designation of "Lamellar Double Hydroxides" (LDHs) has been used in the last few years (Martin and Pinnavaia 1986) and account for the presence of two kinds of metallic cations in the... 

The ratio of trivalent metal reported by various authors are generally in the range 0.14 < x < 0.5. When these values are exclusively obtained by chemical analysis, they appear quite uncertain, especially for the upper and lower limits, since the homogeneity and single-phased nature of the samples is not undoubtedly established. The observed composition limits are generally attributed to the appropriateness of the hydroxylated sheets specific charge with that of the interlamellar domains one. 

As described above, the interlamellar domains are essentially constituted by water molecules and anions. The structural studies, such as single-crystal XRD (Allmann and Lohse 1966 Ingram and Taylor 1967 Allmann 1968a Allmann 1969 Taylor 1973), powder XRD (Espinat, Godart, and Thevenot 1987 Thevenot 1989 de... 

Roy 1990), RMN (Dupuis et al. 1990) and EXAFS (de Roy, Besse, and Bondot 1985) give prominence to the strongly disordered nature of the interlamellar domains. Some physical characteristics of LDHs, such as the wide anionic exchange properties, the evolution of hydration state (vide infra), and the electrical properties (de Roy and Besse 1989 de Roy and Besse 1991) confirm this disordered state. These properties have led some authors to consider that the interlamellar domains present a quasUiquid state (Lai and Howe 1980 Allmann 1968a). 

This leads us to consider that extracrystalline water molecules take part in the global hydration state of the materials. These water molecules adsorbed at the surface of microcrystallites will be designated as extrinsic water molecules in contrast with the intrinsic water molecules located in the interlamellar domains. Therefore, the global hydration n is the sum of two terms the intrinsic hydration n and Ae extrinsic hydration n". The global composition of the material is thus different from that of the crystallites (Figure 7-7). 

The presence of salts or basic salts in the interlamellar domains... 

PoIvtvDes related to the stacking sequences. The strongly disordered description that we used to describe the interlamellar domains leads us to envisage that no particular orientation could occur between two successive hydroxylated sheets. The obtained compounds should be totally turbostratic with a characteristic XRD pattern containing exclusively on the one hand (hkO), reflections related to the well-ordered structure of the sheets, and on the other hand (00 ), reflections related to the stacking of the unoriented sheets. 

The superstructure may also result from the regular alternation of collapsed interlamellar domains (without interlamellar species) with normal anionic domains. Those con unds may be described in the same manner as intercalated graphite. For example, coalingite and coalingite-K [Mg-Fe-C03] (Pastor-Rodriguez and Taylor 1971) present, respectively, periodicities of 12.sA and 17.2A. These values approximately correspond to the sum of the basal spacing of carbonate interlayers (7.56A) and, respectively, one or two brucite-... 

Likewise, the basal spacing of the IH variety could easily be interpreted by the simple insertion of a monolayer of water molecules the experimental results are, however, not fully in accordance with this hypothesis. Surprisingly, if one examines the XRD spectrum, it is obvious that the diffraction lines are sharper for the most hydrated compound, and this is in contradiction with the hypothesis of a disordered layout of sulfate anions and water molecules in the interlamellar domains. Moreover, the IR spectrum... 

The wet compound displays the [Zn-Al-S04] phase, and another one with a periodicity of 17.6A. This last compound could be related to the ap arance of a superstructure by the ordering of the solvated anions in the interlamellar domains of the 8.8A phase. 

A considerable swelling, with intercalation of several monolayers of water and corresponding fortuitously to a twofold increase of the basal spacing, seems to us less probable. Likewise, an interstratification of the 10. A type with another kind of interlamellar domain corresponding to a spacing d 6.1 k should be difficult to justify. 

Monte Carlo Simulations of Semicrystalline Polyethylene Interlamellar Domain and Crystal-Melt Interface... 

Abstract. The interlamellar domain of semicrystalline polyethylene is studied by means of off-lattice Metropolis Monte Carlo simulations using a realistic united atom force field with inclusion of torsional contributions. Both structural as well as thermal and mechanical properties are discussed for systems with the 201 crystal plane parallel to the interface. In so doing, important data is obtained which is useful for modeling semicrystalline polyethylene in terms of multiphase models. Here, we review the main results published previously by us (P.J. in t Veld, M. Hiitter, G.C. Rutledge Macromolecules 39, 439 (2006) M. Hiitter, P.J. in t Veld, G.C. Rutledge Polymer (in press), (2006)]. 

M. Hiitter et al. Monte Carlo Simulations of Semicrystalline Polyethylene Interlamellar Domain and Crystal-Melt Interface, Lect. Notes Phys. 714, 261-284 (2007)... 

The structural, thermal and mechanical characterization of the interlamellar domain and of the 201 crystal-melt interface of semicrystalline PE was performed, and compared with experimental data where available. Monte Carlo simulations complete with three-fold torsional potential were used with a united atom representation of polyethylene. We have employed two different strategies to assess the properties of the interface. 

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