Nanocomposite systems

Maiti and Bhowmick also investigated the diffusion and sorption of methyl ethyl ketone (MEK) and tetrahydrofuran (THE) through fluoroelastomer-clay nanocomposites in the range of 30°C-60°C by swelling experiments [98]. A representative sorption-plot (i.e., mass uptake versus square root of time, at 45°C for all the nanocomposite systems is given in Figure 2.12. 

Most nanocomposite researchers obdurately believe that the preparation of a completely exfoliated structure is the ultimate target for better overall properties. However, these significant improvements are not observed in every nanocomposite system, including systems where the silicate layers are near to exfoliated [29]. While, from the barrier property standpoint, the development of exfoliated nanocomposites is always preferred, Nylon 6-based nanocomposite systems are completely different from other nanocomposite systems, as discussed [3,8]. 

As in PP-based nanocomposite systems, the extended Trouton rule, 3r 0 (y t) = r E (so t), also does not hold for PLANC melts, in contrast to the melt of pure polymers. These results indicate that in the case of P LANC, the flow induced internal structural changes also occur in elongation flow [48], but the changes are quite different in shear flow. The strong rheopexy observed in the shear measurements for the PLA-based nanocomposite at very slow shear rate reflects the fact that the shear-induced structural change involved a process with an extremely long relaxation time. 

Except for the PBS/SAP-qC16 (n-hexadecyl tri-n-butyl phosphonium cation modified saponite) system, the degree of degradation is the same for other samples. This indicates that MMT or alkylammonium cations, and at the same time other properties, have no effect on the biodegradability of PBS. The accelerated degradation of PBS matrix in the presence of SAP-qC16 may be due to the presence of alkylpho-sphonium surfactant. This kind of behavior is also observed in the case of PLA/MMT-based nanocomposite systems. 

In subsequent discussion, we will demonstrate the use and interpretation of some of these techniques. Figure 2a shows typical XRD traces of nanocomposite systems of styrene butadiene rubber (SBR) containing unmodified and modified nanoclay, describing an exfoliated and intercalated nanocomposite [5]. photographs of these systems are also given in the same figure (Fig. 2b, c). In the present case, the information obtained from both the techniques is complimentary. 

Fig. 32 Validation of different permeability models in the PU-based nanocomposite systems...

Thermal and mechanical properties have been drastically improved by nanocomposites [12-33] dispersed with inorganic clays in a polymer matrix, which is characterized by nanometer lengthscale domains. These nanocomposite systems can be similarly examined by the methodology reported in this chapter. 

The individual measurements of the hard grain hysteresis cycles by XMCD have revealed that the hard phase magnetisation show a significant remanence enhancement (Mr/Ms 0.6) [123], This observation implies that the soft phase magnetisation shows remanence enhancement as well. This is in agreement with experimental data on other nanocomposite systems. 

The properties of nanocomposite systems, whose microstructures aim at reproducing real systems, have been examined in various numerical modelling studies [127, 128], In general, the essential features of the hysteresis cycles may be satisfactory reproduced. In particular, soft layer reversal is quantitatively accounted for, which is expected for reversible phenomena. By contrast, the calculated high-field irreversible reversal of the hard phase magnetization is not reproduced in general. Such discrepancy illustrates the already mentioned difficulty to describe irreversible processes. 

These few examples show how the use of nanocomposite systems with hetero polysiloxane type of matrices leads to interesting properties for applications. Further developments using these basic systems are transparent controlled release coatings for anti-fogging systems [41], anti-corrosive systems for metal protection [42], and nanocomposite optical bulk materials [43],... 

Historically, polysiloxane elastomers have been reinforced with micron scale particles such as amorphous inorganic silica to form polysiloxane microcomposites. However, with the continued growth of new fields such as soft nanolithography, flexible polymer electronics and biomedical implant technology, there is an ever increasing demand for polysiloxane materials with better defined, improved and novel physical, chemical and mechanical properties. In line with these trends, researchers have turned towards the development of polysiloxane nanocomposites systems which incorporate a heterogeneous second phase on the nanometer scale. Over the last decade, there has been much interest in polymeric nanocomposite materials and the reader is directed towards the reviews by Alexandre and Dubois (4) or Joshi and Bhupendra (5) on the subject. 

Figure 3. BDS spectra of nanocomposite systems at 40°C. Solid symbols represent real permittivity and hollow symbols represent imaginary permittivity. Squares, circles, up-triangles, down-triangles and diamonds represent levels of 0, 2, 4 and 8% Cloisite respectively.

TGA was utilized to monitor the non-oxidative degradation behavior of the nanocomposite systems as a function of age time. Onset temperatures for non-oxidative degradation were determined from the first derivative of the sample mass. Figures 6 and 7 illustrate the trends in non-oxidative degradation temperature with age time for all systems under both environments. 

TVA was employed in order to characterize the volatile species that were evolved from the nanocomposite systems on aging. The goal of the study was... 

This strongly suggests that these cyclic oligomeric siloxanes are being actively produced within the nanocomposite systems as a result of the thermal aging and are not simply passive residues from the initial synthesis. 

Si/TiB2 and Si/SiC nanocomposite systems, which are similarly generated using HEMM, have also been tested for their electrochemical responses as potential anode materials. These systems consist of a very homogeneous distribution of nanoparticles of silicon in the nanocomposites exhibiting a stable capacity of 350 to 400 mAh/g when tested at a C-rate of These nanocomposite... 

Nowadays nanocomposites are used in a broad variety of technical and scientific fields since they possess useful mechanical and chemical properties. Nanocomposite systems can be derived from different materials. Among these, clays are widely applied because their layered structure with high active surface area and cation exchange capacity has advantages for nanocomposite production. A possible way to improve and accelerate the incorporation of polymers (surfactants) into clay layers is the application of high-intensity ultrasonic treatment on to the suspension of a clay mineral in the presence of polymer (surfactants) molecules. Sonication promotes a drastic decrease of the incorporation time increasing the interlamellar space of clay minerals. 

The aim of this entry is to present a balanced view of the current state of phenolic resins. The patent literature, refereed journals, and other general sources have been utilized to survey the classical and nonclas-sical phenolic resin systems as well as the nanocomposite systems. The article is pedagogical rather than comprehensive. 

The mechanical properties of the C3, C6, and Cl2 nanocomposites were all significantly better than those of the neat phenolic resin, even if a very small amount of the silicate was used. Among the nanocomposites prepared, the organically modified MMT-resol systems showed better mechanical properties than those of the unmodified MMT-resol system. This improvement was attributed to the formation of an end-tethered structure due to the reaction of the carboxylic acid of the organic modifier with the methylol group of the phenolic resin. Thermogravimetric analysis reported by Byun and coworkers showed that the nanocomposite systems had similar thermal stability to that of the neat polymer. 

The work on nanocomposites utilizing novolacs and resols can be considered preliminary and promising. The very subtle differences between novolacs and resols appear to have the potential to contribute to significantly different nanocomposite systems. The distinct separation of the silicate layers may provide the basis for the properties of nanocomposites prepared as novolacs or resols. 

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