Stacked silicate layers

Fig. 9.4 Bright field TEM images of PLA-based nanocomposites prepared with (A) MMT-C1gH3N+, (B) MMT-Clg(CH3)3N+and (C) MMT-2Clg(CH3)2N+. The dark entities are the cross section and/ orfaceofthe intercalated-and-stacked silicate layers and the bright areas are the matrix. Reprinted from [18], 2006, Wiley-VCH.

Scanning transmission electron microscopy (STEM) of the composites fully confirmed the XRD indications. For example, the STEM micrograph in Figure 3.13 shows that mostly single silicate sheets are visible in the PVAcA-10 composite (containing only 43% ammonium cations relative to the number of exchangeable cations in the MMT) despite the presence of a broad shoulder in the XRD (Figure 3.12B), which is probably due to a small amount of stacked silicate layers. 

An excellent Mt dispersion, also at a level of 20 phr, was observed when emulsion blending was adopted, with both individual and stacking silicate layers with a thickness of about 10-30 nm. 

Kim et al [102,103] reported that the toughness of polyamide 12/clay and polyamide 6/clay nanocomposites was enhanced due to the occurrence of some energy dissipating events. They performed in situ tensile tests on thin films of these nanocomposites hi a transmission electron microscope and observed that the major deformation process in these materials was micro-void formation inside the stacked silicate layers. Since the clay interlayer strength is weaker than the clay/matrix interfacial strength, delamination or interlayer debonding... 

PCL-based nanocomposites have also been produced by dissolving the polymer in hot chloroform in the presence of OMLS. "" SAXS and XRD results revealed that the silicate layers forming the clay could not be dispersed individually in the PCL matrix. In other words, the silieate layers existed in the form of tactoids, consisting of several stacked silicate layers. These are responsible for the formation of special geometrical structures in the blends, whieh leads to the formation of superstructures in the thiekness of the blended film. 

The crystal structure of ECS-2 can be described by the stacking of alumino-silicate layers held together by phenylene groups (Fig.l). These layers are composed by aluminum centered tetrahedra bonded to [Si03C] tetrahedra. 

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