Nano Focus: Bottlebrush copolymers expand size range of nanopores
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ano Focus Bottlebrush copolymers expand size range of nanopores
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he wide variety of nanostructured morphologies derived from the selfassembly of block copolymers provides a useful route to nanoporous materials. Degrading one of the polymer blocks leaves a porous network of the remaining polymer, which can be used for filtration and selective crystallization. Their main limitation is the small pore sizes currently accessible, but recent research by J. Rzayev and J. Bolton at the University at Buffalo and T.S. Bailey of Colorado State University shows that this range can be significantly extended by the use of so-called “bottlebrush” copolymers, in which polymer side-chains fan out from a central backbone. The morphology of self-assembled block copolymer materials is normally controlled by altering the length ratio of the two blocks, giving rise to segregated regions in the form of flat planes, cylinders, or spheres. Bottlebrush copolymers, which can have polymer side-chains of different lengths, offer another variable with which to alter the space taken up by each block and thus the morphology they adopt. The research, published in
Energy Focus Light-trapping Si PVs obtained by UV-nanoimprint lithography
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ight-trapping is necessary to achieve low-cost and high-efficiency thinfilm Si photovoltaics devices. Many
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MRS BULLETIN
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VOLUME 36 • APRIL 2011
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photoluminescence studies show a strong 2.7 μm emission band for the codoped Er3+/Pr3+ glass, which is not present for the only Er-doped glass. Analysis of the upconversion spectra in the green visible range shows that this behavior is due to an energy transfer process in which the presence of Pr ions participate, and as a result the 1.55 μm Er emission is weakened while the 2.7 μm emission is
enhanced. Furthermore, peak of calculated emission cross-section in Er3+/Pr3+ doped fluorophosphates glass at 2708 nm achieves (6.57 ± 0.11) × 10−21 cm2 which is higher than the result of Er3+ doped oxyfluoride transparent glass ceramics (4.3 × 10−21 cm2) and ZBLAN glass (5.7 × 10−21 cm2). Rosalía Serna
the January 31st online edition of Nano Letters (DOI: 10.1021/nl103747m), uses asymmetrical bottlebrush polymers consisting of a block with long polystyrene side-chains and one with shorter polyactide side-chains. Using a combination of controlled radical and ring-opening polymerizations, the team synthesized a methacrylate-based block copolymer and then grew the side-chains sequentially from this backbone. Melt pressing and annealing the polymer results in randomly oriented polyactide cylinder domains, which were aligned by channel die processing. Degrading the polyactide chains in alkaline conditions leaves a polystyrene material with nanoscale channels (55 ± 16 nm) running the width of the sample. This represents a substantial increase in size over pores derived from ordinary block copolymers (up to 35 nm), and it is likely that a much greater range is accessible by appropriate tailoring of the side-chains. A potentially useful side effect of fabricating the mate
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