Semiconductor-polymer nanocomposites

Metal sulphide semiconductors/polymer nanocomposites are considered to be highly functional materials with many applications, such as in photoluminescent, photoelectric and non-linear optical materials. The flexibility and processability of polymer matrices can provide good mechanical properties. 

Several assemblies of metal sulphide semiconductors/polymer nanocomposites have been realized by using this method ... 

Stability of common polymers, and consequently, thermal degradation of mercaptide molecules ean be also carried out with the mercaptide dissolved into a polymeric medium. In this case, a finely dispersed inorganic solid phase, embedded in polymer, is generated. Materials based on clusters confined in polymeric matrices are called nanocomposites [Mayer, 1998 Caseri, 2000]. Both semiconductor-polymer and metal-polymer nanocomposites have unique functional properties that can be exploited for applications in several advanced technological fields (e.g., optics, nonlinear optics, magnetooptics, photonics, optoelectronics) [Caseri, 2000]. 

Abstract Semiconductor nanoparticles have attracted much attention due to their unique size and properties. Semiconductor-polymer hybrid materials are of great importance in the field of nanoscience as they combine the advantageous properties of polymers with the unique size-tunable optical, electronic, catalytic and other properties of semiconductor nanoparticles. Due to combination of the unique properties of organic and inorganic components in one material, these semiconductor-polymer hybrids find application in environmental, optoelectronic, biomedical and various other fields. A number of methods are available for the synthesis of semiconductor-polymer hybrid materials. Two methods, i.e. melt blending and in-situ polymerization, are widely used for the synthesis of semiconductor-polymer nanocomposites. The first part of this review article deals with the synthesis, properties and applications of semiconductor nanoparticles. The second part deals with the synthesis of semiconductor-polymer nanocomposites by melt blending and in-situ polymerization. The properties and some applications of semiconductor-polymer nanocomposites are also discussed. 

CdSe-CdS-ZnS core-multishell polymer nanocomposites were prepared by direct dispersion of CdSe-CdS-ZnS core-multishell QDs in an epoxy polymer matrix via a melt mixing technique. Nanocomposites filled with yellow-emitting QDs were more transparent than pure epoxy polymer. A shift in the luminescence of pure epoxy from the blue region to the yellow region was observed in the nanocomposite. Synthesized nanocomposites also showed enhanced tensile properties in comparison to pure epoxy polymer [236]. Several other studied reported the use of a melt blending process for the synthesis of semiconductor-polymer nanocomposites [237-241]. 

Table 1 Some potential applications of semiconductor-polymer nanocomposites...

Semiconductor-polymer nanocomposites have wide range of applications in various fields, including environmental, sensors, solar cells and biomedical applications. Some potential applications of semiconductor-polymer nanocomposites are listed in Table 1. 

Caseri, W. (2000) Nanocomposites of polymers and metals or semiconductors historical background and optical properties. Macromolecular Rapid Communications, 21, 705-722. 

Ramrakhiani [155] has reported the EL in nanocrystals and nanocomposites. Semiconductor nanocrystals exhibit many unique properties, which are promising for the improvement of electroluminescence (EL) devices. Combination of polymer and semiconductor nanocrystals allows the fabrication of flexible and lightweight EL devices. The incorporation of nanocrystals in polymer is expected to increase the life of the device and enhance the brightness of emission. The II-VI semiconductor nanoparticles and the nanocomposites in polymers have been synthesized by chemical route. The samples have been characterized and their electroluminescence has been investigated. 

This bicontinuous-microemulsion polymerization method can also be used to synthesize polymer nanocomposites containing Si02 [101], Ti02, ZnO and many other semiconductors. The advantage of this method is that the nanoparticles of inorganic materials can be dispersed in the polymer matrix fairly uniformly. The only requirement is that nanomaterials should be first stabihzed... 

The more traditional approach has already been used in anodic electrocrystallization processes to produce nanocompositions and superlattices of mixed Ti-Pb oxides [341-347]. With HTSC materials, initial steps have been made in this direction in studies on the electrochemical deposition of conductive polymers on the surface of microband YBCO electrodes [28,50,433]. In the resulting composition, the reversible transition from the HTSC/metal junction (at the high doping degree of the polymer) to the HTSC/semiconductor junction has been achieved. The properties of these compositions allow one to control the shift over a wide interval. 

The y-ray irradiation synthesis method, which can be carried out at ambient temperature and pressure in aqueous or non-aqueous solutions, has been developed to prepare nanomaterials of metals, alloys, elemental chalcogens, chalcoge-nide semiconductors and inorganic/polymer nanocomposites. 

So, the mean size of metal or semiconductor crystals in cryochemically prepared PPX nanocomposites depends almost not at all on the nature of such crystals but is determined by the polymer matrix. In particular, data on the width of the nanocrystals plasmon band [44] (cf. Figures 2.5 and 2.6) specify that d of nanocrystals formed from Ag clusters in CNPPX is, approximately, in one and a halftime less than that of analogous nanocrystals in PPX and CIPPX. 

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