Nanocomposite formation

POLYMERS USED FOR NANOCOMPOSITE FORMATION AND PROPERTIES OF THE NANOCOMPOSITES... 

In order to understand the thermodynamic issues associated with the nanocomposite formation, Vaia et al. have applied the mean-field statistical lattice model and found that conclusions based on the mean field theory agreed nicely with the experimental results [12,13]. The entropy loss associated with confinement of a polymer melt is not prohibited to nanocomposite formation because an entropy gain associated with the layer separation balances the entropy loss of polymer intercalation, resulting in a net entropy change near to zero. Thus, from the theoretical model, the outcome of nanocomposite formation via polymer melt intercalation depends on energetic factors, which may be determined from the surface energies of the polymer and OMLF. 

Choudhury et al. [36] in their work on hydrogenated nitrile butadiene rubber (HNBR)-nanoclay systems showed the thermodynamic aspects of nanocomposite formation using the mean-field-lattice-based description of polymer melt intercalation, which was first proposed by Vaia and Giannelis [37]. Briefly, the free... 

L. Takacs, Nanocomposite Formation and Combustion Induced by Reaction Milling, Mater. Res. Soc. Symp. Proc., 1993, 286,413. 

Su, S., Jiang, D. D., and Wilkie, C. A. Poly(methyl methacrylate), polypropylene and polyethylene nanocomposite formation by melt blending using novel polymerically-modified clays, Polym. Degrad. Stab. (2004), 83,321-331. 

X. Zheng and C.A. Wilkie, Synergy between nanocomposites formation and low levels of bromine and fire retardancy in polystyrene, Polym. Degrad. Stabil., 2003, 81 539-550. 

The fire toxicity of each material has been measured under different fire conditions. The influence of polymer nanocomposite formation and fire retardants on the yields of toxic products from fire is studied using the ISO 19700 steady-state tube furnace, and it is found that under early stages of burning more carbon monoxide may be formed in the presence of nanofillers and fire retardants, but under the more toxic under-ventilated conditions, less toxic products are formed. Carbon monoxide yields were measured, together with HCN, nitric acid (NO), and nitrogen dioxide (NO2) yields for PA6 materials, for a series of characteristic fire types from well-ventilated to large vitiated. The yields are all expressed on a mass loss basis. 

Other characterization methods, such as transmission electron microscopy, are necessary for a more complete evaluation of nanocomposite formation. In a similar case, copper hydroxy dodecyl sulfate, with a bilayer packing of anions was found to result in some nanocomposite formation when used in PVE (5). 

An HDS additive, zinc/copper hydroxy stearate, was melt-blended with low density poly(ethylene). X-ray diffraction analysis of the composite materials was similar to that found with copper hydroxy dodecyl sulfate combined with poly(vinyl ester), where nanocomposite formation was observed, but additional work is necessary for full characterization of the dispersion. The (nano) composites were found to have better thermal stability via TGA and improvement in PHRR in cone calorimetry. However, smoke production was observed to increase. The 5% loading had better overall performance than 10% in terms of thermal stability and most fire properties. 

Figure 16.17. Particulate nanocomposite formation. [Adapted, by permission, from Maeda S, Armes S P, Synthetic Metals, 13, 1995, 151-155.]...

Montmorillonite was used in a two stage process of nanocomposite formation. In the first step, montmorillonite was intercalated with vinyl monomer and then used in the second step to insert polystyrene by in situ polymerization. 

Effect of Fed 3 on Polymerization/Nanocomposite Formation in N-Vinylcarbazole-MMT System... 

FeCl3 is an efficient Lewis acid initiator for the cationic polymerization of monomers like NVC [60]. It is also an efficient dopant for PNVC enhancing its bulk conductivity [61]. Accordingly, in the study of the NVC-MMT polymeriza-tion/nanocomposite formation system, the addition of FeCl3 was considered to be interesting. Results of a recent study [33] (Table 2) indicated that in NVC-... 

Table4. Some typical data for ANI-MMT [(NH4)2S208] polymerization/nanocomposite formation system...

MMT polymerization/nanocomposite formation system addition of FeCl3 increased the percentage loading of PNVC in the composite. 

Polymerization vis-a-vis nanocomposite formation in PY-MMT-water and ANI-MMT-water systems was possible after using FeCl3 and (NH4)2S208 [49] as oxidant respectively in the two systems. Results of recent studies in these systems are presented in Tables 3 and 4, respectively. 

S, Zavyalov, A, Timofeev, A. Pivkina, and J. Schoonman, Metal-polymer nanocomposites formation and properties near the percolation threshold in Nanostructured Materials Selected... 

This perspective method of metal-polymer nanocomposites formation involves the synthesis of both a nanoparticle and its stabilizing polymer matrix in one place (essentially in one stage). Such an approach is conceptually unique, and the systems under consideration are chemically self-regulating ones and thus they have embodied the best solution of the given problem (i.e., the nanoparticles formation and stabilization in polymer systems). Although at present the method is realized on transition metal acrylates and maleinates... 

A current wide set of experimental data concerns mainly the yield characteristics of systems such as nanoparticle distribution in the size and matrix space, physical and chemical properties of the matrix formed, and so on. At the same time, the investigations on the mechanism and kinetics of nanocomposite formation and on understanding how these parameters change during thermal transformations are absent because of the difficulties of the experimental studies of the kinetics of such processes. 

The mechanism involved in the marcaptide termolysis was investigated in the case of silver-based nanocomposite formation. Silver nanoparticles were completely removed from the polymeric matrix by prolonged centrifugation (30min) of nanocomposite samples dissolved in chloroform at 13,000rpm, and... 

Percy and coworkers [39,40] synthesized colloidal dispersions of polymer-silica nanocomposite particles by homopolymerizing 4-vinylpyridine or copolymerizing 4-vinylpyridine with either methyl methacrylate, styrene, n-butyl acrylate or n-butyl methacrylate in the presence of fine-particle silica sols using a free-radical in aqueous media at 60°C. No surfactants were used and a strong acid-based interaction was assumed to be a prerequisite for nanocomposite formation. The nanocomposite particles had comparatively narrow size distributions with mean particle diameters of 150-250 nm and silica contents between 8 and 54 wt.%. The colloidal dispersions were stable at solids contents above 20 wt.%. 

One-pot synthesis approaches have also been developed, involving sonication [23,26], and UV- [15,28] or y-irradiation [27,32,41]. It was found that sonication and y-irradiation resulted in acceleration of the nanocomposite formation by inducing radical formation (i.e. H2O H + OH"). The hydrogen and hydroxyl radicals drive both metal-ion reduction and monomer oxidation. The role of H2O2, either available in the solution or generated through radical recombination, for the enhancement of the rate of polymerization was extensively discussed [23,26]. 

Nanocomposite Formation by Means of Pre-Synthesized Metai Nanoparticies... 

S.S. Kumar, C.S. Kumar, J. Mathiyarasu, and Ki. Phani, Stabilized gold nanoparbcles by reduction using 3,4-ethylenedioxythiophene-polysterenesulfonate in aqueous solutions nanocomposite formation, stability, and appbcation in catalysis, Langmuir, 23, 3401 3408 (2007). 

---