Surface modification of inorganic nanoparticles for development of organic–inorganic nanocomposites—A review

Rapid developments in advanced photonic devices have led to the increasing exploration of high refractive index (high-n) materials, particularly high-refractive-index polymers (HRIP). High refractive indices have been achieved either by introducing substituents with high molar refractions to make intrinsic HRIPs or by combining high-nnanoparticles with polymer matrixes to make HRIP nanocomposites. For intrinsic HRIPs, aromatic rings, sulfur-containing groups, halogens except fluorine and organometallic moieties are often utilized to increase their refractive indices. However, their upper n limitation is usually below 1.80. Incorporation of high-nnanoparticles into polymers seems to be a more promising strategy to achieve a refractive index higher than 1.80; however, the obtained organic–inorganic hybrid materials sometimes suffer from poor storage stability, higher optical loss and poor processability. Besides the refractive index, optical dispersion (Abbe number), birefringence and optical transparency are often involved in designing HRIPs for practical optical fabrications. Therefore, research of HRIPs is becoming an interdisciplinary subject. This feature article reviews recent developments in optical HRIPs and their typical applications in high-tech fields.

High refractive index polymers: fundamental research and practical applications

The control of luminous radiation has extremely important implications for modern and future technologies as well as in medicine. In this Review, we detail chemical structures and their relevant photophysical features for various groups of materials, including organic dyes such as metalloporphyrins and metallophthalocyanines (and derivatives), other common organic materials, mixed metal complexes and clusters, fullerenes, dendrimeric nanocomposites, polymeric materials (organic and/or inorganic), inorganic semiconductors, and other nanoscopic materials, utilized or potentially useful for the realization of devices able to filter in a smart way an external radiation. The concept of smart is referred to the characteristic of those materials that are capable to filter the radiation in a dynamic way without the need of an ancillary system for the activation of the required transmission change. In particular, this Review gives emphasis to the nonlinear optical properties of photoactive materials for the functi...

Nonlinear Optical Materials for the Smart Filtering of Optical Radiation.

Template-Assisted Fabrication of Dense, Aligned Arrays of Titania Nanotubes with Well-Controlled Dimensions on Substrates

This article provides an up-to-date review on nanocomposites composed of inorganic nanoparticles and the polymer matrix for optical and magnetic applications. Optical or magnetic characteristics can change upon the decrease of particle sizes to very small dimensions, which are, in general, of major interest in the area of nanocomposite materials. The use of inorganic nanoparticles into the polymer matrix can provide high-performance novel materials that find applications in many industrial fields. With this respect, frequently considered features are optical properties such as light absorption (UV and color), and the extent of light scattering or, in the case of metal particles, photoluminescence, dichroism, and so on, and magnetic properties such as superparamagnetism, electromagnetic wave absorption, and electromagnetic interference shielding. A general introduction, definition, and historical development of polymer-inorganic nanocomposites as well as a comprehensive review of synthetic techniques for polymer-inorganic nanocomposites will be given. Future possibilities for the development of nanocomposites for optical and magnetic applications are also introduced. It is expected that the use of new functional inorganic nano-fillers will lead to new polymer-inorganic nanocomposites with unique combinations of material properties. By careful selection of synthetic techniques and understanding/exploiting the unique physics of the polymeric nanocomposites in such materials, novel functional polymer-inorganic nanocomposites can be designed and fabricated for new interesting applications such as optoelectronic and magneto-optic applications. Keywords: nano-filler; nano-inclusion; hybrid; effective additive; surface modification; superparamagnetism; UV absorption; in-situ polymerization; dichroism (Published: 2 August 2010) Citation: Nano Reviews 2010, 1: 5214 - DOI: 10.3402/nano.v1i0.5214

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Nanocomposites of polymer and inorganic nanoparticles for optical and magnetic applications

Titania–polymer nanohybrid thin films represent a new class of potential materials for optoelectronic applications. While most such nanohybrid thin films lack control in crystallinity, we report in this paper transparent nanohybrids of titania-polymethyl methacrylate (TiO2–PMMA) thin films having a remarkably enhanced nanocrystallinity. Post-treatments with water vapor at relatively low temperatures were applied on these thin films, following in situ sol–gel polymerization. They promoted rearrangement of flexible Ti–O–Ti bonds leading to enhanced crystallization of the TiO2 phase. The degree of TiO2 crystallinity in the resulting nanohybrid films was studied by using XRD, FTIR, UV–Vis spectroscopies and HRTEM. Both linear and nonlinear optical responses increase with the enhancement of TiO2 crystallinity in the nanohybrids. The highest two-photon absorption coefficient (β) and nonlinear refractive index (n2) were observed for the nanohybrid thin films with highest TiO2 crystallinity, as confirmed by open and closed aperture Z-scan techniques using 250 fs laser pulses at 800 nm, having a value of 2260 cm GW−1 and 6.2 × 10−2 cm2 GW−1, respectively.

Controlling the crystallinity and nonlinear optical properties of transparent TiO2–PMMA nanohybrids

PMMA is one of the most versatile polymeric materials for applications in various technological areas including optics and electro-optics. While the current applications of PMMA in optics and electro-optics are limited by their linear optical behavior, we report here in this paper the unique nonlinear optical behavior of nanohybrids consisting of nanocrystalline TiO2 in PMMA. Transparent thin films of TiO2–PMMA nanohybrid on substrates were synthesized by in-situ sol–gel and polymerisation, assisted by spin coating. Using titanium isoproproxide (Ti-iP) as the starting material for nanocrystalline titania, together with methyl methacrylate and 3-(trimethoxysilyl)propyl methacrylate, nanohybrids containing up to 80% Ti-iP in PMMA were successfully realized. The resulting nanohybrid thin films coated on quartz substrates are optically transparent and demonstrate large nonlinear optical behavior, with an ultrafast response of <1.5 ps. The highest two-photon absorption coefficient (β) and nonlinear refractive index (n2) are observed with the nanohybrid thin film of 60 wt% Ti-iP in PMMA, as confirmed by the Z-scan technique.

Transparent nanohybrids of nanocrystalline TiO2 in PMMA with unique nonlinear optical behavior

Dry synthesis of KAlSiO4 at temperatures from 900 to 1500°C yielded products with slightly different powder X-ray-diffraction patterns. “Orthorhombic” K x Al x Si2− x O4- O1 with x ≈ 1 was obtained as a substantially single phase after heating at 1000°C for one day; we refined its crystal structure from powder X-ray-diffraction data in space group P 1211 [MM = 158.17 g/mol, a 15.669(2), b 9.057(1), c 8.621(1) A, β 90.16(1)°, V 1223.5 A3, Z = 12, Dx = 2.57 g cm−3, RB = 0.080]. It is composed of a relatively open [AlSiO4] framework that is a topological variant of tridymite (t) having the supercell (s) metric a s ≈ 3 a t, b s ≈ a t + 2 b t, c s ≈ c t. The space group P 1211 allows for Al–Si ordering, and refinement of distance-least-squares restrained models, although problematic owing to the pronounced pseudosymmetry, indicates preference for an ordered pattern where Al and Si are distributed on alternating tetrahedra [ d Si–O/ d Al–O = 1.628(1)/1.719(1) A], so that every SiO4 tetrahedron is coordinated to four AlO4 tetrahedra and vice versa . The alternating distribution was independently inferred from 29Si and 27Al MAS NMR spectroscopic data, and the framework model obtained from Rietveld refinement with Si on tetrahedron T 1 could be used to successfully simulate the observed Si(Al4) doublet peak in the 29Si spectrum. Electron diffraction showed that triple twinning with a rotation of 120° around c of the metrically almost hexagonal P 1211 cell is ubiquitous and enhances, in the diffraction experiment, the pseudosymmetry inherited from the tridymite subcell. Furthermore, the diffraction aspect of single individuals ( P *21*) confirms that the screw axes 21-- and --21 of the orthorhombic supergroup P 212121 are only approximated.

THE STRUCTURE OF “ORTHORHOMBIC” KAlSiO4-O1: EVIDENCE FOR Al–Si ORDER FROM MAS NMR DATA COMBINED WITH RIETVELD REFINEMENT AND ELECTRON MICROSCOPY

The properties influencing the photocatalytic activity of TiO2 particles have been suggested to include the surface area, crystallinity, crystallite size and crystal structure. Therefore, manipulation of the microstructure of titania, especially of nanocrystalline powders, is very important in the preparative process. In this study, nanocrystalline TiO2 powders with controlled particle size and phase composition were synthesized at low temperature (<80°C) by a modified sol–gel method. The effects of gelation temperature were systematically investigated. It was found that this parameter played a critical role in determining the crystallinity of single phase anatase. With increasing gelation temperature, the crystallinity of anatase improved initially and then decreased if the temperature was raised to 80°C. These nanomaterials were characterized comprehensively by powder X-ray diffraction (including Rietveld analysis), high-resolution transmission electron microscopy, DSC/TGA thermal analysis and UV–Vis spectrometry.

Ying Li

Papers

Controlling the crystallinity and nonlinear optical properties of transparent TiO2–PMMA nanohybrids

Transparent nanohybrids of nanocrystalline TiO2 in PMMA with unique nonlinear optical behavior

THE STRUCTURE OF “ORTHORHOMBIC” KAlSiO4-O1: EVIDENCE FOR Al–Si ORDER FROM MAS NMR DATA COMBINED WITH RIETVELD REFINEMENT AND ELECTRON MICROSCOPY

CONTROLLED SYNTHESIS AND CHARACTERIZATION OF TiO2 NANOPARTICLES VIA A SOL–GEL METHOD