Rare-Earth-Doped Bromide Materials Display Lasing Activity at Near-Infrared Transitions
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Rare-Earth-Doped Bromide Materials Display Lasing Activity at Near-Infrared Transitions Long-wavelength infrared light sources are important for a variety of applications, including remote sensing, night vision, and
medical diagnosis. However, almost all solid-state materials that exhibit lasing at these wavelengths are easily damaged by moisture, making them difficult to use outside of the laboratory. Now, K. Rademaker, S.A. Payne, and W.F. Krupke of Lawrence
Protein-Based Thermoplastic Elastomers Biochemically Synthesized Genetic engineering methods can now be used to prepare multiblock protein copolymers. It is well known that synthetic multiblock copolymers can form biphasic materials that exhibit, to varying degrees, the mechanical and chemical properties of the constituent blocks. Property tuning can be effected by controlling interphase mixing of incompatible blocks. Interphase mixing, in turn, depends on the range of microstructures accessible to the blocks, which is much larger for systems comprising large, well-defined blocks. Recently, researchers at Emory University and the Georgia Institute of Technology demonstrated that, by synthesizing large multiblock protein copolymers, material microstructure at both the nanoscale and mesoscale can be systematically modified in a manner that was previously unfeasible. As reported in the January 25 issue of Macromolecules (p. 345; DOI: 10.1021/ ma0491199), K. Nagapudi of the Emory University School of Medicine and the Georgia Institute of Technology, E.L. Chaikof of the Emory University School of Medicine, V.P. Conticello of Emory University, and co-researchers used a recombinant DNA technique to synthesize a new class of protein BAB triblock copolymers, whose respective blocks exhibit distinct elastomeric (A) and plastic (B) mechanical properties analogous to synthetic thermoplastic elastomers, where A = VPGVG[(VPGVG)2VPGEG(VPGVG)2]48VPGVG and B = VPAVG[(IPAVG)4(VPAVG)]16IPAVG Knowing from previous research that elastin-mimetic proteins display an inverse temperature profile for self-assembly, the researchers chose the sequence of the hydrophilic elastomeric A block so that its transition temperature (Tc) is substantially higher than 37°C (physiological temperature) and the sequence of the hydrophobic plastic B block so that its Tc is close to room temperature. When casting films, the researchers observed that their triblock copolymer protein reversibly self-assembled from concentrated aqueous solution at a temperature above the B block’s Tc to form a network of plastic microdomains dispersed in a continuous elastomeric phase composed of the A blocks. The researchers said that the ability of the B blocks to form virtual cross-links and to maintain plastic deformation behavior in the absence of chemical or radiation cross-linking was completely unanticipated. Through rational choice of film processing conditions that control mesoscale and nanoscale structure, the researchers observed increases in the Young’s modulus of more than three order
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