Nanoparticle exfoliation

An important factor in study of thermal stability of synthetic mbber nanocomposites is the dispersion of the nanoparticle on the matrix. The presence of nanoparticles exfoliated influences the thermal or fire behavior of nanocomposite [83]. 

The majority of studies have used surfactants that wrap around nanocarbons via van der Waals interactions [37]. For instance, surfactants such as sodium dodecylsulfate (SDS) are commonly used to disperse CNTs in aqueous solutions [38,39] while other surfactants, such as Pluorinc-123, are used to mechanically exfoliate graphene from graphite flakes (Fig. 5.4(a)) [40,41]. The polar head group of the surfactant can be used to further hybridize the nanocarbon via a range of covalent or noncovalent interactions [42]. For example, nanoparticles of Pt [43,44] and Pd [45] have been decorated onto SDS-wrapped MWCNTs. Similarly, Whitsitt et al. evaluated various surfactants for their ability to facilitate the deposition of Si02 NPs onto SWCNTs [46,47]. As an exam-... 

Morphology evolution is thus found to be dependent on the processing technique applied to disperse the nanoparticles. The latex-blended and prevulcanized nanocomposites show predominant exfoliation with some intercalation, especially in uncured and prevulcanized samples. In conventionally cured but latex-blended nanocomposites, realignment of NA particles is visible, with a greater tendency of NA platelets towards agglomeration. In solid state mixing, the dispersion is still poorer. XRD studies also corroborate the above observations. 

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. 

It was also noticed by the same authors19 that the incorporation of the OMMT in EVA instead of PA6, keeping constant the global composition, led to a strong decrease in heat released, but with a different evolution of HRR as a function of time. This was ascribed to different morphologies of clays (mixed intercalated/exfoliated versus completely exfoliated) for the polymer blend. Consequently, the formulation process of complex FR systems involving polymer blends and made up of nanoparticles in combination with FRs seems crucial. 

Nanoparticles of metals such as Au, Ag, Pd and Pt embedded in exfoliated sheets of aminociays of the type R8Si8Mgs0lfi-(OH)4, where R = CH2CH2NH2 are entirely water soluble. These sheets of the composite come to the organic-aqueous interface on addition of alkane thiols to the aqueous layer. 

In the present study the property of the aminociays wherein protonation of the amino groups in water is accompanied by exfoliation has been exploited.15 Thus metal nanoparticle composites formed by the exfoliated aminoclay sheets by carrying out the reduction of metal precursors in the presence of the clay have been investigated. Besides being entirely water soluble, the exfoliated sheets of aminoclay-Au nanoparticle composites move to the organic/aqueous interface in the presence of an alkanethiol. 

In conclusion, exfoliated sheets of Mg-phyllo(organo)silicates containing pendant amino groups have been used to stabilize Au, Ag, Pd and Pt nanopartides. The nanoparticle-decorated day sheets can be easily dispersed in water. These metal nanopartides... 

Scheme 3. The earliest stages of the process of PE thermal oxidative degradation in the presence of exfoliated MMT nanoparticles.

Notably, while the hydroperoxides accumulation starts at lower temperatures in PE-n-MMT than in the unfilled PE (cf. e. g., Figure 8), the clearly visible mass loss of the nanocomposite (attributable solely to decomposition of the accumulated hydroperoxides) ensues at lower temperatures as well. It is reasonable to suggest that this effect is caused by a catalytic action of exfoliated MMT nanoparticles on the hydroperoxides decomposition. 

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