Exfoliation-absorption, layered

In conventional polymer composites, the interlayer spacing will remain the same, similar to clay, and there will therefore be no shift of the diffraction peak. But if there is intercalation, the peak position will shift to a lower angle than in the original nanomaterial. The absence of a characteristic diffraction peak is usually the first indication of exfoliation of the nanomaterial, although it is not conclusive. However, several other factors such as a decrease in the degree of coherent layer stacking, very low concentration of nanomaterial and strong absorption by heavy atoms/ions (e.g. bromide) may also affect the accuracy of this analysis. 

Absorption bands from stretching of silicon oxygen bonds (Si-0) occur in the region of 950-1100 cmThis is particularly important for layered clay-based bionanocomposites because Si-O bonds are present in clay. The absorption band for agglomerated clay layers (tactoids) is broad. The absorption band becomes narrower as the degree of exfoliation increases. Thus, FUR spectroscopy can be irsed to determine the extent of exfoliation in bio-nanocomposites (Klein et al., 2005). Absorption bands associated with different bonds of montmorillonite are shown in Table 1. 

In the 1960s there were studies of absorption of monomers by clays [116, 117]. In more recent years, monomers such as caprolactam were absorbed into organo clays and were subsequently polymerized. The most important of these efforts involved Toyota researchers [118 to 125] using caprolactam. These products were called nanocomposites and seem to contain polyamide intercalated between silicate layers or had exfoliated structures. Other monomers have also been absorbed into montmorillonite and polymerized. These include the formation of polyimides [126], epoxy resins [127], and polylactones [128]. 

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