Intercalated morphology

In the literature, there are several reports that examine the role of conventional fillers like carbon black on the autohesive tack (uncured adhesion between a similar pair of elastomers) [225]. It has been shown that the incorporation of carbon black at very high concentration (>30 phr) can increase the autohesive tack of natural and butyl rubber [225]. Very recently, for the first time, Kumar et al. [164] reported the effect of NA nanoclay (at relatively very low concentration) on the autohesive tack of BIMS rubber by a 180° peel test. XRD and AFM show intercalated morphology of nanoclay in the BIMS rubber matrix. However, the autohesive tack strength dramatically increases with nanoclay concentration up to 8 phr, beyond which it apparently reaches a plateau at 16 phr of nanoclay concentration (see Fig. 36). For example, the tack strength of 16 phr of nanoclay-loaded sample is nearly 158% higher than the tack strength of neat BIMS rubber. The force versus, distance curves from the peel tests for selected samples are shown in Fig. 37. 

For the system with very high adhesion strength between the clay and the stickers, the favorable enthalpy of the sticker-clay interaction dominates the unfavorable entropic contributions. Accordingly (Figure 11c), the composite now becomes exfoliated, as demonstrated by both compressible and incompressible models. Interestingly, within the compressible model, the old minimum at H 1.6-2 nm has not disappeared completely, indicating the presence of a metastable intercalated morphology. 

Huang, J.-C. Zhu, Z.-k Yin, J. Qian, X.-F. Sun, Y.-Y., Poly(etherimide)/montmori]lonite nanocomposites prepared by melt intercalation Morphology, solvent resistance properties and thermal properties, Polymer 2001, 42, 873-877. 

Studies indicate the formation of an intercalated morphology in the nanocomposites due to favorable interactions between the polymer matrix and the clay. The morphology of the nanocomposite is intricately linked to the amount of silicate in the system. With clay content >15 wt%, mechanical properties are further improved but the formation of an apparent superlattice structure correlates with a loss in the electrical properties of the nanocomposite [25]. 

Fig. 7. Schematic representation of various methods (Solution blending, melt blending, and in situ polymerization). The delaminated (or exfoliated) and intercalated morphologies are shown.

They partially retain the ordered intercalated morphology in some regions, with the presence of few partially delaminated (into constituent sub-domains) and intercalated domains randomly dispersed in the matrix. In that way, they assume almost the same structure as that of intercalated NCs, except the presence of floccus formed due to the localized interaction... 

The PP-g-HMA nanocomposites, with 1, 3, and 5wt% of an MMT modified by cation exchange with cetyl pyridinium chloride, were prepared in xylene solution at 120°C for 6h. The powdery products were sandwiched between cover glasses and melted at 200°C to form thin films, which were then cooled with a rate of 20°C min i. The XRD and TEM analyses showed that the nanocomposites possess a mixed exfoliated/intercalated morphology, with a level of exfoliation that increases as the clay loading is lowered. Since PP-g-HMA contains more than one functional group per chain, the structure of the nanocomposites is probably similar to that of Figure 3.8c. 

Using a sHghtly different tact, Akat et al. investigated exchanging a chain transfer agent (diethyl octyl ammonium ethylmercaptan bromide, 42) [50] onto MMT prior to the free radical polymerization of PS. They found that while PMMA nanocomposites formed with this modified clay led to exfoHated structures, PS nanocomposites led to intercalated morphologies. 

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