Tactoids defined

FIGURE 10.4 Electron micrograph of a swollen n-butylammonium vermiculite prepared in a 0.1 M solution of n-butylammonium chloride. The scale is defined by the white bar, which represents 200 nm. The three large arrows indicate packets of vermiculite layers, or tactoids. In the region between the two smaller arrows, the layers appear to be individually separated. 

We do have to be careful in the way we apply the definition of a phase to the n-butylammonium vermiculite system. According to Gibbs [13], a phase is any homogeneous and physically distinct part of a system that is separated from other parts of the system by definite boundary surfaces. Because the gel can be lifted out of the supernatant fluid on a spatula, it clearly justifies description as a phase in the latter sense, but it is inhomogeneous on the nanometer-to-micron (colloidal) length scale. It can only be defined as homogeneous on the macroscopic length scale. The same considerations apply to the tactoid phase. 

Filler dispersion is defined at different levels macro-dispersion, which characterizes the incorporation of fillers into the matrix, micro-dispersion, which describes the random distribution of aggregates, tactoids and primary particles within the polymer matrix, and nano-dispersion, which is fundamental for obtaining structural information on nanofillers. 

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