Optical properties, of nanocomposites

Size monitoring and design of optical properties of nanocomposites... 

As the local electric field in the particles is enhanced at the SPR, the metal nonlinear optical response can be amplified as compared to the bulk solid one. Moreover, the intrinsic nonlinear properties of metals may themselves be modified by effects linked with electronic confinement. These interesting features have led an increasing number of people to devote their research to the study of nonlinear optical properties of nanocomposite media for about two decades. Tire third-order nonlinear response known as optical Kerr effect have been particularly investigated, both theoretically and experimentally. It results in the linear variation of both the refraction index and the absorption coefficient as a function of light intensity. These effects are usually measured by techniques employing pulsed lasers. 

As for the linear optical response, different approaches have been proposed to describe the nonlinear optical properties of nanocomposite media. Nevertheless, a few general principles can be identified. First, each component of such a medium possesses its own susceptibility however, as the typical structure size is much smaller than the wavelength, the observable result of light interaction with the medium is different from a simple combination of the individual responses of the separated constituents (again, we do not treat the case of spatially-resolved studies of die optical response). One is then again led to introduce the concept of effective medium, extended to the case of nonlinear optical properties. 

This formulation can be also obtained by other approaches [81, 83, 87, 88]. It is extensively used in the literature to analyse the nonlinear optical properties of nanocomposite materials determined experimentally. 

Metal nanopartides can also be cited. The characteristic properties of metal nanopartides and nanocomposites have been the subject of study because of their unique optical properties. Combining metal and polymer together enhances the optical properties of nanometals. Srivastava et al. 3] studied the optical properties of gold nanocomposites by changing the size and fraction of gold nanopartides. The optical properties of nanocomposite films of various thicknesses with different sizes and volume fraction of gold nanopartides have been studied using spectroscopic... 

But not only the dimensions and the concentration is enough to obtain an optically transparent material. The morphology and the aggregation of inorganic particles can influence the optical properties of nanocomposites. Nanometric-sized particles compared to micron-sized particles have higher surface/volume ratio. When the particle size decreases, the percentage of molecules/atoms present on the surface is increased. For this reason, the interpartide interactions due to forces such as van der... 

The optical properties of nanocomposites prepared with poly(styrene-maleic anhydride) copolymer coated with alumina nanopartides and polycarbonate as matrix was evaluated by Chandra et al. [8]. The transparendes were compared for samples with 2 mm thick polycarbonate neat resin, the samples of nanocomposites containing 1 and 2 wt% of treated alumina, and a sample containing 2 wt% of untreated alumina. The samples were put on top of a pattern, as shown in Figure 6.3. The sample with 1 wt% of treated alumina was the most transparent among the samples containing nanopartides, even though some haziness could be observed. 

The results of the analysis are reported as absorbance or transmittance. Some examples of the use of spectrophotometry in the characterization of optical properties of nanocomposites with polymer matrix and different nanoparticles are discussed in the following sections. 

The branched polysaccharide dextran is assembled with alkanethiol-modified gold nanoparticles and the resulting nanocomposite is then functionalized to facilitate the specific binding of target biomolecules. This biorecognition process can be easily detected by particle plasmon resonance (PPR), based on the optical properties of gold nanoparticles [163]. 

Sanchez, C., Lebeau, B., Chaput, F. and Boilot, J.P. (2003) Optical properties of functional hybrid organic-inorganic nanocomposites. Advanced Materials, 15, 1969-1994. 

The remaining sections outline recent findings on the optical properties of metal-dendrimer nano-composites. The sections have been organized into areas of interest related to the fabrication as well as photophysical properties of these new and important materials. The first section discusses some of the important issues concerning the fabrication of these novel materials and their chemical characterization. The second section discusses the linear and nonlinear optical properties of these materials. The third section provides details related to the ultrafast emission properties of gold- and silver-dendrimer nanocomposites. 

While the linear absorption and nonlinear optical properties of certain dendrimer nanocomposites have evolved substantially and show strong potential for future applications, the physical processes governing the emission properties in these systems is a subject of recent high interest. It is still not completely understood how emission in metal nanocomposites originates and how this relates to their (CW) optical spectra. As stated above, the emission properties in bulk metals are very weak. However, there are some processes associated with a small particle size (such as local field enhancement [108], surface effects [29], quantum confinement [109]) which could lead in general to the enhancement of the fluorescence efficiency as compared to bulk metal and make the fluorescence signal well detectable [110, 111]. 

OPTICAL PROPERTIES OF RIGID PVC/ MONTMORILLONITE NANOCOMPOSITES WITH EPOXY RESIN AS COMPATIBILIZER... 

Polyvinyl chloride/montmorillonite nanocomposites were prepared using an epoxy resin, as compatibiliser, and the effect of this compatibiliser on the optical properties of the nanocomposites investigated. It was found that the transparency of the nanocomposites improved with increasing content of montmorillonite, which was pretreated with the epoxy resin. The good transparency of the nanocomposites also indicated that the epoxy resin improved the processing stability of the nanocomposites. 3 refs. 

Sipe JE, Boyd RW (2002) Nanocomposite materials for nonlinear optics based on local field effects, in optical properties of nanostructured random media, 82nd edn. Springer, Berlin, pp 1-19... 

Hydrodynamic and optical properties of polymers [NP(OR)2]n [R = CH2CF3, CH2(CF2)2H, CH2(CF2)4H] have been analysed. Mechanical properties of polyphosphazene-silicate nanocomposites, prepared from (NP[(0CH2CH2)20Me]2 n (MEEP) and tetraethoxysilane, have been investigated as function of the catalyst used. ... 

The new water soluble highly stable metal-polysaccharide nanocomposites of noble metals have been fabricated within the framework of the new approach to the synthesis of hybrid nanosized materials on the basis of arabinogalactan. Distinctive optical properties of the nanoparticles are demonstrated as the plasmonic resonance. Nanobiocomposites with target optical characteristics have a great potential to design promising multifunctional materials with controlled optical properties as well as new optical systems and optical markers in medicine. 

Electron behavior, optical properties, catalytic properties, conductivity, and magnetic properties of nanocomposites were discussed in an extensive review pa-per. Complementary use of electron paramagnetic resonance and nuclear magnetic resonance helped to understand chain mobility in nanocomposites obtained from poly(ethylene oxide) encapped with triethoxy silicon. This nanocomposite is composed of PEO chains attached to silica clusters. It was found that chain fragments close to the silica clusters have hindered mobility due to the reduction of local free volume. The length of this hindered segment is estimated as three ethylene oxide units. 

In the first part, emphasis will be put on the linear optical properties of dielectric media doped with noble metal nanoparticles. Indeed, the study of the linear response is definitely needed to further explore the nonlinear one. We will then introduce the fundamentals of the theoretical tools required to understand why and how people inquire into the third-order nonlinear properties of nanocomposite materials. In the second part, experimental results will be presented by first examining the different nonlinear optical phenomena which have been observed in these media. We will then focus on the nanoparticle intrinsic nonlinear susceptibility before analysing the influence of the main morphological factors on the nonlinear optical response. The dependence of the latter on laser characteristics will finally be investigated, as well as the crucial role played by different thermal effects. 

LINEAR OPTICAL PROPERTIES OF NOBLE METAL NANOPARTICLES AND NANOCOMPOSITE MEDIA... 

As for the linear properties, numerous approaches have been proposed to predict and explain the nonlinear optical response of nanocomposite materials beyond the hypothesis leading to the simple model presented above ( 3.2.2). Especially, Eq. (27) does not hold as soon as metal concentration is large and, a fortiori, reaches the percolation threshold. Several EMT or topological methods have then been developed to account for such regimes and for different types of material morphology, using different calculation methods [38, 81, 83, 88, 96-116]. Let us mention works devoted to ellipsoidal [99, 100, 109] or cylindrical [97] inclusions, effect of a shape distribution [110, 115], core-shell particles [114, 116], layered composites [103], nonlinear inclusions in a nonlinear host medium [88], linear inclusions in a nonlinear host medium [108], percolated media and fractals [101, 104-106, 108]. Attempts to simulate in a nonlinear EMT the influence of temperature have also been reported [107, 113]. 

C. Structural and optical properties of CiKsiUca nanocomposite films prepared by co-sputtering deposition. Appl. Surf. Sci. 226. 52-56 (2004)... 

Yang, G., Wang, W.-T., Yang. G.-Z., Chen, Z.-H. Enhanced nonlinear optical properties of laser deposited Ag/BaTiO3 nanocomposite films. Chin. Phys. Lett. 20, 924-927 (2003)... 

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