Disordered tactoid

In general, for the type of partieles used here, that is, natural clays with medium (ea. 1 pm) lateral-size platelets, even with favorable thermodynamics for polymer nanoconq)osite fonnation, tlie conq)osite structure is almost always characterized by the coexistence of exfoliated, intercalated, and disoid ed lay. Thus, a silent XRD may hide a large number of disordered tactoids, whereas an XRD with an intercalated peak does not reveal tlie extent of exfoliation. 

Figure 3.2 X-ray diffraction pattern of a clay-polymer composite that would appear to be exfoliated but actually contains disordered tactoids.

Figure 3.3 Schematic representation of a disordered tactoid illustrating how a series of d-spacing would give rise to a featureless X-ray diffraction pattern.

Figure 3.6 contains an image of a disordered tactoid. It can be seen that the spacing between plates varies widely and the resulting diffraction pattern would be as in Figure 3.2. 

In addition, a tactoid containing n sheets in such a disordered state is separated from an adjacent tactoid containing n sheets by inter-tactoid pores. If two adjacent tactoids are tilted with respect to one another, very complicated architecture may exist within the suspension. The description of such architectures should be performed in terms of correlation functions relating the spaces occupied by solids or by voids. Such an analysis is difficult for anisotropic objects. 

It has been shown that oiganoclay platelets aggregation in packets (tactoids) results in laige-scale disorder intensification that reduces nanofiller anisotropy degree. In its turn, this factor decreases essentially... 

TEM is a very common analytical technique that can produce high resolution photographs of nanoparticles in polymer matrices. This technique can yield accurate information on the level of exfoliation, the distance between partieles, and the spacial distribution of nanoparticles. Figure 3.4 contains the TEM image of a well-exfoliated composite of montmoril-lonite in nylon 6. The clay plates appear as dark lines in a light gray matrix. The teehnique can also yield pictures of tactoids and disordered structures mentioned previously when discussing X-ray diffraction. 

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