Phase segregation, nanocomposites

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... 

Fig. 29 Different morphologies encountered in polymer-layered silicate nanocomposites phase segregated left), intercalated middle), and exfoliated nanocomposites right)...

Figure 4.17 Different morphologies encountered in polymerlayered silicate nanocomposites. (Left) Phase segregated (center) intercalated (right) exfoliated nanocomposites.

In this paper we have demonstrated the application of gas-phase combustion processes to produce nanocomposites with superparamagnetic properties. The combustion process was designed in such a way as to allow for the rapid formation of nano-liquid droplets which would phase segregate, combined with rapid quenching to preserve the microstructure and chemical composition. The resulting material showed superparamagnetic behavior between 155 K and room temperature. 

EL emission from ZnO nanoparticles/lV, V -diphenyl-V, V -bis(3-methylphenyl)-l,l -biphenyl-4 -diamine (TPD) PMMA nanocomposite devices was also investigated by Lee et al. [36]. For fabrication of the ZnO-organic nanocomposite EL devices, the phase-segregation method was used, and the ZnO NCs and TPD PMMA were separated into two layers. The method improved the probability of recombination of electrons and holes within the ZnO nanoparticles. Maximum EL emission peak was observed at 392 nm, which corresponded to the band-gap energy of ZnO nanocrystals at a drive voltage of 7 V [36]. 

Nanocomposite coatings, which require thermo-dynamically driven phase segregation. The superhardness of nanocomposites lies in the nanostructured condition of the coatings, whose structural stability could result from a spinodal... 

Mauroy, H., Rozynek, Z., Plivelic, T.S.S., Possum, J.O., Helgesen, G., Knudsen, K.D., 2012. Oxygen-controlled phase segregation in poly(A-isopropylacrylamide)/Laponite nanocomposite hydrogels. Langmuir 29, 371—379. 

Figure 13.2 Different morphologies encountered in polymer-layered silicate nanocomposites (a) phase segregated, (b) intercalated and (c) exfoliated nanocomposites.

The in situ partide generation methods also allow for the preparation of highly ordered nanocomposites. Block copolymers of hydrophilic and hydrophobic blocks tend to phase segregate and form micelles when solubilized in either hydro-phobic or hydrophilic solvents. These micdles can be used as nanotemplates for partide synthesis. Metal salts will bind sdec-tivdy to the hydrophilic part of the block copolymer. Dependent on the polarity of the chosen solvent the hydrophilic block will build either the core of the micelles or the corona. The domain size and morphology are mainly determined by the voltrme fraction of each block and the total molecular wdght of the block copolymer. 

In addition, we have to take into account that metal oxide-based nanocomposites have specific structure. Research on such a two-phase system, in which the concentration of the second oxide phase is much less than the concentration of the base oxide, has shown that the second phase, as a rule, is finely dispersed on the surface of the base oxide grains (Szezuko et al. 2001 Pagnier et al. 2000 Carreno et al. 2002). Possible versions of segregation layers of foreign cations on the surface of SnOj grains are shown in Fig. 14.4 (Varela et al. 1999 Carreno et al. 2002). It has been established... 

In general, the dispersion of clay particles in a polymer matrix can result in the formation of three general types of composite materials (Figure 1). Conventional composites contain clay tactoids with the layers aggregated in unintercalated face - face form. The clay tactoids are simply dispersed as a segregated phase. Intercalated clay composites are intercalation compounds of definite structure formed by the insertion of one or more molecular layers of polymer into the clay host galleries and the properties usually resemble those of the ceramic host. In contrast, exfoliated polymer-clay nanocomposites have a low clay content, a monolithic structure, a separation between layers that depends on the polymer content of the composite, and properties that reflect those of the nano-confmed polymer. 

TPO adds an additional complexity to the process of preparing polymer nanocomposites. The apparent surface energy associated with the interface between the dispersed rubber phase (polyethylene) in polypropylene will provide segregation regions for the organomontmorillonite. This will prejudice the preferred alignment of the montmorillonite and compromise performance. 

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