Silicate gallery

Li, Y. and Ishida, H. Concentration-dependent conformation of alkyl tail in the nanoconfined space Hexadecylamine in the silicate galleries, Langmuir (2003), 19, 2479-2484. 

Moreover the evolution of the XRD during annealing can be modeled to determine the apparent diffusivity, D, of the polymers within the silicate gallery. Namely, the ratio of the amount of intercalated polymer at time t, Q(t), to that at equilibrium Q(°°) is [30] ... 

A schematic representation of a TSLS complex is provided in Figure 1. On the basis of preliminary XRD and stochiometric studies, it appears that the imogolite tubes are in van der Waals contact, most likely in a log-jam-like array in the layer silicate galleries. Although the tubes stuff the galleries, two unique adsorption environments are available, namely, the intra-and inter-tube pores designated A and B in Figure 1. 

The layered nanocomposites can be obtained as shown in Figure 16.20. Intercalation ofe-caprolactone into the silicate galleries was done simply by suspending... 

FIGURE 5.90 Schematic presentation of two extremes of composite structures that can be obtained by polymer melt intercalation of layered silicates. The rectangular bars represent individual silicate layers (1 nm thick), (a) Single polymer layers intercalated in the silicate galleries, (b) Delamination (exfoliation) of layered silicates and dispersion in a continuous polymer matrix. (After Giannelis, E. R 1996. Adv. Mater., 8(1), 29. With permission.)... 

Incarnate and co-workers [2004] reported that at constant clay content the CPNC modulus increases with the extrusion rate. Addition of clay shifted the main E" peak position by about 60 to 70°C. The same authors [2003] also investigated the viscoelastic properties of a PA-6 and its statistical, partially aromatic copolymer, ADS, with 3, 6 and 9wt% C30B. In tensile mode the low-T relative modulus, increased from 1.15 to 1.54 (at 1 Hz and 5°C/min). The influence of clay on Tg might be attributed to the confinement of polymer chains in silicate galleries, which partially hinders the molecular motion [Ash et al., 2002]. It is significant that Tg does not always increase with organoclay content, as the outcome is influenced by the type, quantity, and miscibility of the plasticizing intercalant. 

Natural montroriUonite and organically modified MMT with methyl tallow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) were evaluted in starch-based nanocomposite [232]. It was observed that the TPS/ Cloisite Na-t nanocomposites showed higher tensile strength and thermal stability, better barrier properties to water vapor than the TPS/Cloisite 30B nanocomposites, as well as the pristine TPS, due to the formation of the intercalated nanostructure. Perez et al. [233] compared three different clays (Cloisite Na+, Cloisite 30B and Cloisite 10A) and found the best properties were achieved with Cloisite lOA due to their greatest compatibility with the matrix. 

Finally, the acid- or base-catalyzed reaction of hydrolysis and condensation polymerization of TEOS into a layered silicate gallery could affect the physical properties of silica-pillared magadiite and kenyaite. The samples that were silica-pillared by acid- and base-catalyzed reactions show a large increase in basal spacing. Also, they exhibit relatively narrow pore size distributions and show high surface areas, depending on the type of catalyst and layered silicate. These results indicate that variations in the conditions of gelation contribute to the improvement in the physical properties of silica-pillared molecular sieves. 

Figure 10.3 Much simplified view of the expansion of the layer silicate gallery resulting from ion exchange with a long chain organic cation...

Polymer melt intercalation (involving a polymer and a layered siUcale mixture heated under discontinuous or continuous shear above the softening point of the polymer thus, the polymer chains diffuse from the molten polymer into the silicate galleries and form intercalated or exfoliated sheets). 

Figure2Id shows the Arrhenius diagram of the relaxation times, obtained by the dieiectric reiaxation spectroscopy (DRS) for bulk poly(methylphenylsiloxane) (PMPS) and PMPS intercalated as 1.5-2.0 nm films between organically modified silicate layers [41]. Unlike the slow cooperative glass transition dynamics in the bulk PMPS, PMPS confined within the silicate galleries is characterized with very fast, almost Arrhenius segmental dynamics (compare with the relaxation map in Fig. 15). The similar result was also obtained for organic molecules located within the well-defined pores and channels with sizes less than 1 nm [39]. As revealed.

In melt intercalation, the polymer and layered silicate mixture is annealed above the Jg in either static or flow conditions. Modified layered silicates are usually employed to promote intercalation. The polymer chains spread from the molten mass into the silicate galleries to form either intercalated or delaminated hybrids according to the degree of penetration. The critical factor that determines which type is obtained is probably linked to thermodynamic factors. This method is environmentally benign due to the absence of organic solvents. Furthermore, it is compatible with current industrial processes such as extrusion and injection molding. However, very careful attention has to be paid to finely tune the processing conditions to increase the compatibility of the clay layer surfaces with the polymer matrix. 

From a thermodynamic viewpoint, both the entropic and enthalpic factors are important in controlling the dispersion of clay layers in a polymer matrix [19-21]. It was reported that the confinement of the polymer chains inside the silicate galleries results in a decrease in the overall entropy of the macromolec-ular chains [10,20] this is, however, compensated by the increase in conformational freedom of the tethered alkyl surfactant chains as the inorganic layers separate due to the less confined environment (Figure 11.2). It was also shown that apolar interactions are generally unfavorable and so in the case of nonpolar polymers, there is no favorable excess enthalpy to promote the dispersion of clay platelets and it is hence necessary to improve the interactions between the polymer and clay so as to become more favorable than the alkylammonium-clay interactions. This can be achieved by functionalization of the polymer matrix or addition of compatibilizers [3,18,22-29]. For polar polymers, an alkyl-ammonium surfactant is adequate to offer sufficient excess enthalpy and promote the formation of exfoliated nanocomposites. 

Addition of several types of days as well as modified (organophiHzed clays) were found to improve mechanical properties and decrease water uptake of starch-based bionanocomposites viz., natural sodium montmoriUonite (MMT) [155], MMT, hectorite, hectorite modified with 2-methyl, 2-hydrogenated taUow quaternary ammonium chloride and kaolinite [150], natural sodium montmoriUonite (Na MMT, Cloisite Na+), and organically modified montmoriUonite (OMMT) with methyl taUow bis-2-hydroxyethyl ammonium cations located in the silicate gallery (Cloisite 30B) [151], MMT (hydrophilic Cloisite Na+ day and hydrophobic Qoisite 30B, lOA, and 15A) [152, 153). 

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