Nanocomposite structure

Unlike the heterostructures whose periodic structure must be accurately controlled, the formation of nanocomposite structure is self-organized based upon thermodynamically driven spinodal phase segregation [118-121]. For the CVD... 

At the co-deposition of nanocomposite components formation of M/SC particles proceeds simultaneously with formation of a dielectric matrix, and the relationship between these processes determines the nanocomposite structure. This problem has been in detail investigated for the case of M/SC nanoparticles formation in polymer matrices. Synthesis of nanocomposite films by simultaneous PVD of polytetrafluoroethylene (PTFE) and Au has been carried out in works [62-64], Polymer and metal were sputtered under action of Ar ions and then the obtained vapors were deposited on substrates (quartz, glass, silica, mica, etc.) at various temperatures. Here, it is necessary to note that polymer sputtering cannot be considered as only physical process PFTE polymer chains destruct under action of high-energy ions, and formed chemically active low-molecular fragments are then deposited and polymerized on a substrate surface. 

Shape of granules essentially affects the properties of granular metal. Concerning the nanocomposite structure, it is possible to outline fibrous and laminate composites together with grain nanocomposites, in which shape of granules is close to spherical. In fibrous composites, sizes of inclusions in... 

V. Krikorian, M. Kurian, M. E. Galvin, A. P. Nowak, T. J. Deming, and D. J. Pochan, Polypeptide-based nanocomposite Structure and properties of poly(L-lysine)/Na+-montmoril-lonite, J. Polym. Sci. Part B Polym. Phys. 40, 2579—2586 (2002). 

Incorporation of modified clays into thermosetting resins, and particularly in epoxy35 or unsaturated polyester resins, in order to improve thermal stability or flame retardancy, has been reported.36 A thermogravimetric study of polyester-clay nanocomposites has shown that addition of nanoclays lowers the decomposition temperature and thermal stability of a standard resin up to 600°C. But, above this temperature, the trend is reversed in a region where a charring residue is formed. Char formation seems not as important as compared with other polymer-clay nanocomposite structures. Nazare et al.37 have studied the combination of APP and ammonium-modified MMT (Cloisite 10A, 15A, 25A, and 30B). The diluent used for polyester resin was methyl methacrylate (MMA). The... 

The nature of the organomodifier plays a role in the existence of true nanocomposite structures (intercalated for 15A and 30B, exfoliated for 25A, microcomposite for 10A), cone calorimeter results associated with x-ray diffraction (XRD) suggest that increased flame retardancy are more dependent on physical and thermal cross-linking of clay particles and polymer chains than on formation of nanocomposite structure. However, it can be concluded that the role of clay is crucial since PHRR values are reduced up to 70% in the presence of clays. 

In the work of Wilkie et al.,55,56 oligomers of styrene, vinylbenzyl chloride, and diphenyl vinyl-benzylphosphate and diphenyl vinylphenylphosphate (DPVPP) have been prepared and reacted with an amine and then ion-exchanged onto clay. The resulting modified DPVPP clays have been melted blended with polystyrene and the flammability was evaluated. XRD and TEM observations proved the existence of intercalated nanocomposite structures. Cone calorimeter tests have shown a substantial reduction in the PHRR of about 70% in comparison with pure PS. According to the authors, this reduction was higher than the maximum reduction usually obtained with PS nanocomposites. Other vinylphosphate modified clay nanocomposites were also elaborated. The reduction in PHRR was greater with higher phosphorus content than for DPVPP. Consequently, the reduction in PHRR seemed attributed to both the presence of the clay and to the presence of phosphorus. 

Nanotube nanocomposites with a large number of polymer matrices have been reported in the recent years. The composites were synthesized in order to enhance mechanical, thermal and electrical properties of the conventional polymers so as to expand their spectrum of applications. Different synthesis route have also been developed in order to achieve nanocomposites. The generated morphology in the composites and the resulting composite properties were reported to be affected by the nature of the polymer, nature of the nanotube modification, synthesis process, amount of the inorganic filler etc. The following paragraphs review the nanocomposites structures and properties reported in a few of these reports and also stress upon the future potential of nanotube nanocomposites. 

Intercalated and partially exfoliated PVC-clay nanocomposites were produced by melt blending in the presence and absence of DOP and characterised by X-ray diffraction and transmission electron microscopy. The effects of various factors, including volume fraction of clay, plasticiser content, melt compounding time and annealing, on nanocomposite structure and the thermal and mechanical properties of the nanocomposites were also examined. It was found that the best mechanical properties were achieved at 2% clay loading and 5 to 10% DOP loading. 18 refs. 

The mechanical properties of the nanocomposites strongly depend on their structure, orientation of the filler, phase separation, and processing conditions. Hence, there is a need for in situ nondestructive characterization technique to probe the internal stress in nanocomposite structures. The shortcomings of many conventional techniques such as low resolution, destructive measurements, complex modeling and applicability to only certain class of materials are overcome by using pRS owing to the sensitivity and nondestructive measurement for monitoring internal stress in various materials [59]. 

The fire-retardant mechanism associated with nanoclays has recently been studied and is likely to involve the formation of a ceramic skin which catalyzes char formation by thermal dehydrogenation of the host polymer to produce a conjugated polyene structure. " The nanocomposite structure present in the resulting char appears to enhance the performance of the char through reinforcement of the char layer. These effects would explain the apparent fire-retardant synergy observed when nanoclays are incorporated into polymer formulations containing condensed phase fire-retardant systems, including coated fillers. 

There are many other characterization methods (e.g., small-angle X-ray scattering, solid-state nuclear magnetic resonance, and Fourier-transformed infrared analysis) for investigating nanocomposite structure. These techniques are extensively reviewed in Ray and Okamoto. ... 

In one example, the tensile strength of polyamide 6 was increased by 55% and the moduli by 90%, with the addition of only 4wt% of delaminated clay. The enhanced tensile property of PCN suggests that nanocomposite performance is related to the degree of clay delamination, which increases the interaction between the clay layers and the polymers. Several explanations, based on the interfacial properties and the mobility of the polymer chains, have been given for this reinforcement. Kojima et al. reported that the tensile modulus improvement for polyamide 6-clay hybrid originated from a constrained region, where the polymer chains have reduced mobility. The dispersion and delamination of the clay were the key factors for the reinforcement. The delaminated nanocomposite structure produces a substantial increase in modulus. 

Polymer clay nanocomposites exhibit very low flammability. For instance, the heat release rate during the combustion of polyamide 6-clay nanocomposite is reduced by 63% with a clay content of 5wt%. The nanocomposite structure also enhances the property of the char through reinforcement of the... 

In addition to the traditional use in paints as viscosity regulator, bentonite is currently used in the development of new materials with nanocomposite structures. 

Because of the small size of nanotubes (<1 nm) and their excellent mechanical and electrical properties (depending on the hexagonal lattice and chirality), they have been recognized as ideal for nanocomposite structures. The relative tensile strength of theses structures can be as high as 200 GPa, with Young s moduli as high as 1 TPa. 

Capek, I. (2006) Nanocomposite Structures and Dispersions. Elsevier, London. 

Tailored Nanocomposite Structures for Improved Polymer Performance... 

Pozsgay et al. (12) showed, using XRD and TEM, the nanocomposite structure achieved by compounding HdPC modified clay and polypropylene, and... 

Nanocomposite structures, consisting of quantum dots embedded in glass or a semiconductor material, can be used in current optical and electro-optical devices. 

ELECTRICAL CONDUCTIVITY AND ELECTROLUMINESCENCE OF PLANAR NANOCOMPOSITE STRUCTURES ... 

TEM analysis of the nanocomposite with an A1 content beyond the percolation threshold reveals spherical pure metal nanoparticles with a mean diameter of about 10 nm (Fig. 6a), while below the percolation threshold the composite contains agglomerates of rhombohedral AI2O3 (corundum) with a mean size of 55 nm (Fig. 6c). A sample with a metal content just at the percolation threshold contains metal nanoparticles of 10nm and alumina aggregates of 28 nm in diameter (Fig. 6b). The inorganic phase is homogeneously dispersed within the polymeric matrix in all of the investigated samples. It has been shown that the nanocomposite structure determines the oxidation behaviour of A1 nanoparticles within the polymeric matrix under air exposure. 

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