Exfoliated morphology

Morphological structures and properties of a series of poly(ethyl acrylate)/clay nanocomposites prepared by the two distinctively different techniques of in situ ATRP and solution blending were studied by Datta et al. [79]. Tailor-made PNCs with predictable molecular weights and narrow polydispersity indices were prepared at different clay loadings. WAXD and studies revealed that the in situ approach is the better option because it provided an exfoliated morphology. By contrast, conventional solution blending led only to interlayer expansion of the clay gallery. 

In numerous works dealing with the combination of nanoparticles and FR compounds, surface modifications of nanoparticles were only aimed to promote good dispersion of the nanoparticles into the polymer matrix (with intercalated or exfoliated morphologies for layered silicates as nanoparticles), even in the presence of the usual FRs, for example ammonium polyphosphate (APP) or magnesium hydroxide (MH). The initial aim was to combine the individual effects of each component to achieve strong synergistic effects. 

TEM investigations and TGA analysis under oxidative atmosphere evidenced that the PE-clay nanocomposites were characterized by an intercalated/exfoliated morphology and a higher onset decomposition temperature (Figure 6.14). 

The commonality between the surfactants described in this section is that they do not contain a reactive group which is capable of reacting with styrene. It has been found that for these types of nonreactive surfactants, although styrene monomer can intercalate between the clay layers, exfoliated morphologies have not been achieved for in-situ polymerized PS nanocomposites. 

Bulk polymerization initiated via more novel methods have also been used to form bulk PS-MMT nanocomposites. Zhang et al. [19] used gamma irradiation to initiate the polymerization of PS-MMT nanocomposites with different surface modifications (3, 34) and successfully prepared exfohated morphologies when reactive clay modifications were used. Uthirakumar et al. [51-54] modified MMT with a cationic radical initiator which was used to initiate the bulk polymerization of styrene. Because the polymerization was initiated from the clay surface and the monomer and the clay were suitably compatible, exfoliated morphologies were formed. 

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