Nanocrystal composites

Research on semiconductor nanoparticle technology by chemists, materials scientists, and physicists has already led to the fabrication of a number of devices. Initially, Alivisatos and co-workers developed an electroluminescence device from a dispersion of CdSe nanoparticles capped with a conducting polymer349 and then improved on this by replacing the polymer with a layer of CdS, producing a device with efficiency and lifetime increased by factors of 8 and 10, respectively. 0 Chemical synthetic methods for the assembly of nanocrystal composites, consisting of II-VI quantum dot polymer composite materials,351 represent one important step towards the fabrication of new functional devices that incorporate quantum dots. 

In order to prepare SWNT-Au nanocrystal composites, SWNTs were functionalized by amidobutane (with a terminal azide group) as follows. Acid-treated SWNTS were reacted with thionyl chloride, followed by reaction with 4-azidobutylamine. These SWNTs were reacted with hexy-nethiol-capped Au nanocrystals. 

The sensitivity of these sensors was defined as a signal change upon exposure to the known concentrations of vapors. Sensitivity of the 2.8-nm CdSe nanocrystals was 0.8 PL counts/Torr of methanol with almost no detectable sensitivity to toluene. The sensitivity of the 5.6-nm CdSe nanocrystals was 2.9 PL counts/Torr of methanol and 8.8PL counts/Torr of toluene. Although this environmental sensitivity was compatible with earlier reported sensors based on polished or etched bulk CdSe semiconductor crystals3940 and polymer-nanocrystals composites,16 the sensor reported here had a more selective response to polar and nonpolar vapors due to the multiwavelength PL from different-size nanocrystals incorporated into the polymer film. The response and recovery kinetics of PL from the 2.8-nm nanocrystals in PMM A upon exposure to methanol were very fast (<0.5 min). However, 5.6-nm nanocrystals in the same sensor film exhibited a much longer response and recovery times upon interactions with methanol, 4 and 20min, respectively. The 5.6-nm nanocrystals had 4-min response and 0.5-min recovery times upon interactions with toluene. 

GreenhamN. C, Peng X. and Alivisatos A. P. (1996), Charge separation and transport in conjugated-polymer/semicondnctor-nanocrystal composites studied by photoluminescence quenching andphotocondnctivity , Phys. Rev. B 54, 17628-17637. 

Fig. 6. Schematic diagram of the various excitation, charge transfer, and decay pathways available in a conjugated polymer nanocrystal composite (Salafsky, 1999)...

TABLE 7.4 Quantum Dot Emission Wavelength as a Function of Nanocrystal Composition and Size... 

Cellulose nanocrystals have been used in the elaboration of ceramics [170, 171], Shin and Exarhos [170] have prepared porous Titania by using a template process with cellulose nanocrystals. A colloid suspension of cellulose nanocrystals was added into titanium (IV) bis(ammonium lactate)dihydroxide (Tyzor-LA) to form a Tyzor-LA-cellulose nanocrystals composite. After calcination at 500 °C in air, a porous structure was obtained. 

A. Watt, E. Thomsen, P. Meredith, H. Rubinsztein-Dunlop, A New Approach to the Synthesis of Conjugated Polymer Nanocrystal Composites for Heterojunction Optoelectronics. Chem. Commun. 2004,2334. 

H. Wei, H. Sun, H. Zhang, G. Gao, B. Yang, An Effective Method to Prepare Polymer/Nanocrystal Composites with Tunable Emission over the Whole Visible Light Range. Nano Res. 2010, 3, 496-505. 

N. Greenham, X. Peng, A. Alivisatos, Charge Separation and Transport in Conjugated-Polymer/Semiconductor-Nanocrystal Composites Studied by Photoluminescence Quenching and Photoconductivity. Physical Review B 1996,54,17628-17637. 

Cells by Improved Nanocrystal Composition. Solar Energy Materials and Solar Cells 2011, 95, 3227-3232. 

Li, Y.Q., Rizzo, A., Cingolani, R., and Gigli, G. (2006) Bright white light-emitting devices from ternary nanocrystal composites. 

A wet-chemical method for production of CTS/HAp nanocrystal composites at low temperature has been demonstrated by Murungan and coworkers [140]. Limitations associated with nanoHAp, such as bioresorption and particle migration, can be alleviated by this approach. The rate of bioresorption of nanoHAp was improved by the addition of CTS, and the viscoelastic nature of the composites prevented the migration of particulate matter into the surrounding tissue upon postimplantation. In addition to these, the smoothness of the composites prevents the soft tissues around the implant from damage. 

H. Liu, S. Cui, S. Shanga, D. Wang, and J. Song, Properties of rosin-based waterborne polyurethanes/cellulose nanocrystals composites. Carbohydr. Polym. 96, 510-515 (2013). 

Ruan, D., Zhang, L., Zhang, Z.,and Xia, X. Structure and properties of regenerated cellulose/ tourmaline nanocrystal composite films. J. Polym. Sci. Part B Polym. Phys., 42, 367-373 (2003). 

Zhou C, Chu R, Wu R, Wu Q (2011) Electrospun polyethylene oxide/ceUulose nanocrystal composite nanofibrous mats with homogeneous and heterogeneous microstmctures. Biomacromolecules 12 2617-2625. doi 10.1021/bm200401p... 

Polymer/Semi- conductor-Nanocrystal Composites Studied by Photolu- minescence Quenching and Photoconductivity, Physical Review B 54 (1996) 17628-17637 ... 

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