Montmorillonite exfoliated tactoids

Figure 6.21 Exfoliated tactoids of montmorillonite. Note the irregular shapes of exfoliated platelets compared to the larger tactoids in Figures 6.18-6.19.

Lan, T. Kaviratna, P.D. Pinnavaia, T.J. Mechanism of clay tactoid exfoliation in epoxy-clay nanocomposites. Chem. Mater. 1995, 7, 2144-2150. Wang, M.S. Pinnavaia, T.J. Clay polymer nanocomposites formed from acidic derivatives of montmorillonite and an epoxy-resin. Chem. Mater. 1994, 6, 468-474. Pinnavaia, T.J. Intercalated clay catalysts. Science 1983, 220, 365-371. 

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. 

As discussed in the previous chapter concerning the structure of smectite clays, it was pointed out that these clays are turbostatic and have WAX patterns that only exhibit 001 or hkO reflections with no hkl reflections. The hkO reflections are invariant and can be used to confirm the presence of the clay in a composite at any level of exfoliation. The 001 reflections are a result of the basal spacing between the clay plates as stacks in tactoids. These peaks are highly variable and are dependent upon a number of variables, including level of exfoliation, intercalate type, and level of order. Figure 3.1 illustrates these two types of reflection for montmorillonite intercalated with dodecylpyrrolidone surface treatment where the peak at approximately 20° two theta is of the hkO type and the peaks at 2.58, 5.26, and 7.84 are of the 001 type. The three peaks are related, being the 001, 002, and 003 reflections. 

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