Silicates polymer intercalation

Komori, Y. and Kurada, K. (2000). Layered silicate - Polymer Intercalation Compounds, In Pinnavaia, T.J. and Beal, G.W. (eds). Polymer Layered Silicate Nanocomposites, Wiley, New York. 

Rheology of various polymer layered-silicate nanocomposites - intercalated, exfoliated and end-tethered exfoliated (prepared by in-situ polymerization from reactive groups tethered to the silicate surface), have been performed in a conventional melt-state rheometer in both oscillatory and steady shear modes. These experimental studies have provided insight into the relaxation of polymer chains when confined by the layers of inorganic silicates, as well as the role of shear in orienting the layered nanocomposites. 

Intercalation materials, in which different nanostructured components are attached to the porous matrix. This is the case of metal and metal oxide nanoparticles generated into zeolites and mesoporous silicates or organic polymers intercalated between laminar hydroxides. 

XRD is a rather simple and widely used technique for the characterization of a layered-clay dispersion in a polymer matrix. WAXS analysis was used to quantify the height between adjacent silicate platelets, and subsequently to prove the widening of this distance as the matrix polymer intercalates between the galleries. Changes in the value of 20 reflect changes in the... 

V. Mehrotra and E.P. Giannelis, Metal-insulator molecular multilayers of electroactive polymers intercalation of polyaniline in mica-type layered silicates. Solid State Commun., 11, 155-158 (1991). 

Fig.1 Schematic illustration of different possible structures of layered silicate polymer composite (a) microcomposite (b) intercalated nanocomposite (c) exfoliated nanocomposite [12]...

Schematic of polymer intercalation in the silicates in the presence of PP-g-MA. (Reproduced from Kawasumi, M. et al.. Macromolecules, 30,6333,1997.)...

It has been generally assessed that the mechanism of interaction among the components of PO/day nanocomposites involves the functionalities of the functional polymer used as matrix or compatibilizer. The most frequent explanation is related to the hydrophilic/ hydrophobic balance of components involving some kind of undefined polar interaction between the silicate layers and the functional polymer (Alexandre and Dubois 2000, Sinha Ray and Okamoto 2003, Pavlidou and Papaspyrides 2008). The direct intercalation/interac-tion of a wide numbers of MAH-grafted low-molecular-weight compounds with layered silicates has been studied suggesting that the anhydride can promote the intercalation even if this is not a modeling of polymer intercalation (Sibold et al. 2007). 

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]. 

Vaia, R. A. and Giannelis, E. P. 1997. Lattice model of polymer intercalation in organically modified layered silicates. Macromolecules 30 7990-7999. 

Mehrotra V, Giannelis EP (1992) Nanometer scale multilayers of electroactive polymers -intercalation of polypyrrole in mica-type silicates. Solid State Ionics 51 115-122... 

Figure 1.8 Schematic of polymer intercalation in the silicates using melt mixing approach. Reproduced from Ref [27] with permission from American Chemical Society.

The insertion of PEO into mica-like sheet silicates in the reactions of a melt of the polymer with the host Na - or NH4 -exchanged lattice is one of tiie few examples of direct polymer intercalation. Poly(ethylene oxide) is also inserted into the lamellar networks of V205-nH20, MoOs," " - MnPSj, CdPSj, " etc. Thus an aqueous solution of PEO (M = 10 ) reacts with an aqueous gel of V2O5 nH20 to form a composite after removal of water. In this case, the interlayer distance increases from 1.155 to 1.32nm. Alkali metal ions react with PEO to form inclusion compounds. These can also be inserted into layers of ionic silicates, for example, into MMN. The distance between the layers of the PEO-Li salt complexes intercalated into MMN is 0.8 nm, the PEO chain adopts a slightly strained helicoid conformation in these locations. 

The nylon-clay nanocomposites were prepared by in situ polymerization in the presence of organically modified, with aminolauric acid, montmorillonite. The reaction between nylon monomer and modified montmorillonite rendered nylon chains end-tethered though aminolauric acid to the silicate surface leading to exfoliated silicates (61). However, not all polymer nanocomposite systems could be produced via in situ polymerization processes because of the chemical sensitivity of polymerization catalysts. Direct melt blending of hydrophilic polymers with montmorillonite in its pristine state or polymers with surfactant-intercalated montmorillonite was found to be possible to deliver polymer intercalated or exfoliated nanocomposites (62,63). 

Various methods have been developed in order to prepare pol3uner-layered silicate nanocomposites. These include in situ polymerization, polymer intercalation in... 

Intercalated polymer-clay nanocomposites have been synthesized by direct polymer intercalation (4-6), and in situ intercalative polymerization of monomers in the clay galleries (7, 8). Owing to the spatial confinement of the polymer between the dense clay layers, intercalated polymer-clay nanocomposites can exhibit impressive conductiviw (6) and barrier properties (7). The exfoliation of smectite clays provides 10 A-thick silicate layers with high in - plane bond strength and asjJect ratios comparable to those found for fiber reinforced polymer composites. 

Typical examples of two-dimensional structures (layered particles) are clay silicate particles, containing many layers with a high aspect ratio, approximately 1 nm thick and up to several microns long. The principle used in polymer/clay nanocomposites is to separate not only clay aggregates but also individual layers in the polymer (intercalation and exfoliation see Fig. 6.11). 

Based on the interaction between the polymer matrix and layered silicate polymer layered silicate nanocomposites are classified into intercalated and exfoliated nanocomposites [56-58]. Figure 7 represents the intercalated and exfoliated nanocomposites along with the conventionally filled microcomposite. 

Vaia R A and Giannelis E P (2001) Liquid Crystal Polymer Nanocomposites Direct Intercalation of Thermotropic Liquid Crystalline Polymers into Layered Silicates, Polymer 42 1281-1285. 

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