Core-shell nanostructure

Kang N, Perron ME, Prudhomme RE et al (2005) Stereocomplex block copolymer micelles core-shell nanostructures with enhanced stability. Nano Lett 5 315-319... 

This strategy was first realized by Lozinsky et al., who studied the redox-initiated free-radical copolymerization of thermosensitive N-vinylcaprolactam with hydrophilic N-vinylimidazole at different temperatures, as well as by Chi Wu and coworkers. Lozinsky presents an extensive review of the experimental approaches, both already described in the literature and potential new ones, to chemical synthesis of protein-like copolymers capable of forming core-shell nanostructures in a solution. 

McBride J, Treadway J, Feldman LC, Pennycook SJ, Rosenthal SJ (2006) Structural basis for near unity quantum yield core/shell nanostructures. Nano Lett 6 1496-1501... 

Zhou, W., et al., A general strategy toward graphene metal oxide core-shell nanostructures for high-performance lithium storage. Energy Environmental Science, 2011. 4(12) p. 4954-4961. 

In this chapter, two carbon-supported PtSn catalysts with core-shell nanostructure were designed and prepared to explore the effect of the nanostructure of PtSn nanoparticles on the performance of ethanol electro-oxidation. The physical (XRD, TEM, EDX, XPS) characterization was carried out to clarify the microstructure, the composition, and the chemical environment of nanoparticles. The electrochemical characterization, including cyclic voltammetry, chronoamperometry, of the two PtSn/C catalysts was conducted to characterize the electrochemical activities to ethanol oxidation. Finally, the performances of DEFCs with PtSn/C anode catalysts were tested. The microstmc-ture and composition of PtSn catalysts were correlated with their performance for ethanol electrooxidation. 

Optical nanoprobes are preferably designed as core/shell nanostructures where the optically active material is located in the core. A general schematic of such a nanoparticle is indicated in Fig. 1 and the typical synthesis steps are as follows ... 

Santra S, Liesenfeld B, Bertolino C, Dutta D, Cao Z, Tan WH, Moudgil BM, Mer-icle RA (2006) Fluorescence lifetime measurements to determine the core-shell nanostructure of FlTC-doped silica nanoparticles An optical approach to evaluate nanoparticle photostability. J Luminesc 117 75-82... 

Figure 10 shows a schematic of the formation of a single chain core-shell nanostructure. It is known that the short grafted PEO chains have an average... 

Fig. 10 Schematic of formation of a single chain core-shell nanostructure through the coil-to-globule transition of the PNIPAM-g-PEO copolymer chain backbone [67]...

As discussed before, the lower value of Rg)/ Rh) confirms that the collapsed chain has a core-shell nanostructure and the collapsed PNIPAM core is denser than the swollen PEO shell. In comparison with a uniform sphere with the same (R ), the denser core leads to a smaller (Rg). The increase of (Rg)/ (J h) in the range 35-40 °C reflects the core-shell structure and becomes more uniform in density because the PEO chains in the shell are forced to overlap each other when the PNIPAM core continues to shrink (Fig. 14c). In Fig. 15, it is the further increase of (Rg)/(Rh) in the range 40-50 °C that differentiates the two scenarios. Namely, if the first one was correct, (Rg)/(Rh) should decrease because the core becomes denser. On the other hand, in the second scenario, the collapse of the PEO chains increases the chain density of the shell so that the core-shell nanostructure becomes more uniform, as... 

In an LLS study, Zhang et al. [94] dissolved this well-characterized PNIPAM-seg-St copolymer in deionized water for 10 days to ensure complete dissolution. The final concentration used was 7.2 E - 7g/mL and it was clarified with a 0.5 pm Millipore Millex-LCR filter to remove dust. Note that in their experiment, the scattering volume ( 10 pL) still contained 105-106 copolymer chains so that the number of density fluctuations was not a problem even in such a dilute solution. Their original objective was to determine whether such a copolymer chain could self-fold into the predicted singleflower-like core-shell nanostructure. 

Using this approach, hydrophilic (neutral or ionic) comonomers, such as end-captured short polyethylene oxide (PEO) chains (macromonomer), l-vinyl-2-pyrrolidone (VP), acrylic acid (AA) and N,N-dimethylacrylamide (DMA), can be grafted and inserted on the thermally sensitive chain backbone by free radical copolymerization in aqueous solutions at different reaction temperatures higher or lower than its lower critical solution temperature (LCST). When the reaction temperature is higher than the LOST, the chain backbone becomes hydrophobic and collapses into a globular form during the polymerization, which acts as a template so that most of the hydrophilic comonomers are attached on its surface to form a core-shell structure. The dissolution of such a core-shell nanostructure leads to a protein-like heterogeneous distribution of hydrophilic comonomers on the chain backbone. 

For copolymers with some protein-like comonomer distributions, individual copolymer chains can memorize or inherit its parent globular state namely, their folding back into the core-shell nanostructure is much easier, resulting in a smaller and denser single-chain particle in comparison with their counterparts, randomly distributed comonomers on the... 

It is possible to alter the intrinsic properties of materials by chemical nanocoating, which cannot be achieved by conventional methods. Generally the core-shell nanostructures are divided into two categories (1) lanthanides doped in the core (2) lanthanides doped in the shell. The former are synthesized in order to improve the quantum efficiency of lanthanide ions or design bio-labels, while the latter are meant for the study of surface modifications on the lanthanide luminescence or the synthesis of lanthanide-doped hollow nanospheres. 

Sun X, Liu J, Li Y. Oxides C core-shell nanostructures one-pot synthesis, rational conversion, and Li storage property. Chem Mater 2006 18 3486-3494. 

Figure 11.56 Left, Sdiematic illustration of the growth pathways for the Au Ag core-shell nanostructures. Right, representative TEM images of Au Ag core-shell nanoprisms with a gold frism core. The scale bar is the same for all images. Reproduced with permission from reference [131]. (2007) Wiley-VCH Verlag GmbH Co. KGaA.

Wu et al. reported on a rod—coil diblock copolymers based on mesogen-jacketed liquid crystalline polymer as the rod block and polystyrene as the coil block (Scheme 6).82 Styrene was polymerized by TEMPO mediated radical polymerization, followed by sequential polymerization of 2,5-bis[4-methoxyphenyl]oxy-carbonylstyrene (MPCS) to produce the rod—coil diblock copolymer (20) containing 520 styrene and 119 MPCS repeating units. The rod—coil copolymer was observed to self-assemble into a core—shell nanostructure in a selective solvent for polystyrene... 

Figure 26. Schematic representation of a core—shell nanostructure formed by a self-assembly of 20 in a selective solvent.

Mathur, S. Shen, H. Sivakov, V. Werner, U. Germanium nanowires and core-shell nanostructures by chemical vapor deposition of [Ge(C5H5)2j. Chem. Mater. 2004, 16 (12), 2449-2456. 

To demonstrate high efficiency of core-shell nanostructures we estimate the gain factor in the core-shell nanociystals with the shell made of SiC, focusing on the... 

Prior attempts at nanocomposite dielectrics made no attempt to control the nanostructure of the polymer/dielectric material through controlling the chemistry between the nanoparticle and the dielectric. The first example of the use of a well characterized core-shell nanostructured dielectric material appeared in 2005 [35]. Researchers at Bell Labs used narrowly dispersed anatase phase titanium oxide nanoparticles (rod-shaped -15 x 4 nm K = 31) as the high-A core material (see... 

Xu, R, Zhang, X., Lu, J., Xi, W., Hong, 1., and Xie, Y. 2003b. y-Irradiation route to photoluminescent CdS-CdSe with core-shell nanostructures under ambient conditions. Can. J. Chem. 81 381. 

Chen, Y, Zhu, C. and Wang, T. (2006) The enhanced ethanol sensing properties of multi-walled carbon nanotubes/Sn02 core/shell nanostructures . Nanotechnology, 17,3012-17. 

Preparation of noble metal/Cr203 (core/shell) nanostructures on GaN ZnO was conducted through a stepwise photodeposition under oxygen-free conditions [17, 18]. The scheme is shown in Fig. 10. First, noble metal nanoparticles were deposited using a proper metal salt complex under band gap irradiation of GaN ZnO (1 > 400 nm). The as-prepared noble metal/GaN ZnO sample was then treated with K2Cr04 in a similar manner. The final product was washed thoroughly with distilled water and dried overnight at 343 K. 

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