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RISS 인기검색어
- 검색키워드
- 저자 : Uher, C. (검색결과 4 건)
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Anisotropic hybrid particles based on electrohydrodynamic co-jetting of nanoparticle suspensions
Hwang, Sangyeul,Roh, Kyung-Ho,Lim, Dong Woo,Wang, Guoyu,Uher, Ctirad,Lahann, Joerg Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.38
<P>Electrohydrodynamic co-jetting of two different nanocrystal suspensions can result in anisotropic nanocomposite particles. Using this approach, we are able to prepare submicron-sized, spherical Janus particles (464 ± 242 nm), which are not only comprised of two chemically distinct compartments, but are also morphologically anisotropic. Specifically, multifunctional hybrid particles have been derived, which are composed of a crosslinked copolymer, poly(acrylamide-<I>co</I>-acrylic acid) (p(AAm-<I>co</I>-AA)), and compartmentalized with respect to two metal oxides, <I>i.e.</I> titanium dioxide (TiO<SUB>2</SUB>) and magnetite (Fe<SUB>3</SUB>O<SUB>4</SUB>). Due to size as well as optical color differences between the Fe<SUB>3</SUB>O<SUB>4</SUB> (∼10 nm) and TiO<SUB>2</SUB> (<100 nm) loadings, the surface morphology of the two compartments are significantly different and the particles display magnetic, optical, and interfacial anisotropy. Magnetic anisotropy of the particles has been utilized to control the particles' positioning in an external magnetic field, which—with further work—may lead to magnetically switchable surfaces for display applications.</P> <P>Graphic Abstract</P><P>Polymeric Janus particles with distinguishable surface morphology and magneto-optical properties are prepared by electrohydrodynamic co-jetting of Fe<SUB>3</SUB>O<SUB>4</SUB> and TiO<SUB>2</SUB> suspensions. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp00264j'> </P>
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Ultralow thermal conductivity of β -Cu<sub>2</sub>Se by atomic fluidity and structure distortion
Kim, Hyoungchul,Ballikaya, Sedat,Chi, Hang,Ahn, Jae-Pyung,Ahn, Kiyong,Uher, Ctirad,Kaviany, Massoud Elsevier 2015 Acta materialia Vol.86 No.-
<P><B>Abstract</B></P> <P>We demonstrate a prototype thermal evolution path for liquid thermal conductivity in solids. Thermal evolution of β -Cu<SUB>2</SUB>Se shows large interstitial displacement of constituent atoms marked by glass-like transitions and an asymptotic liquid thermal transport. Using ab initio molecular dynamics (AIMD), we identify these transitions, and confirm them with in situ transmission electron microscopy and electron energy loss spectroscopy. The thermal disorder of the Cu<SUP>+</SUP> ions forms homopolar Cu–Cu bonds under a rigid Se framework, and at yet higher temperatures the Se framework undergoes thermal distortion. The non-equilibrium AIMD prediction of lattice thermal conductivity shows significant suppression of the phonon transport, in agreement with experiments and molecular behavior.</P>
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Stretchable nanoparticle conductors with self-organized conductive pathways
Kim, Yoonseob,Zhu, Jian,Yeom, Bongjun,Di Prima, Matthew,Su, Xianli,Kim, Jin-Gyu,Yoo, Seung Jo,Uher, Ctirad,Kotov, Nicholas A. Nature Publishing Group, a division of Macmillan P 2013 Nature Vol.500 No.7460
Research in stretchable conductors is fuelled by diverse technological needs. Flexible electronics, neuroprosthetic and cardiostimulating implants, soft robotics and other curvilinear systems require materials with high conductivity over a tensile strain of 100 per cent (refs 1, 2, 3). Furthermore, implantable devices or stretchable displays need materials with conductivities a thousand times higher while retaining a strain of 100 per cent. However, the molecular mechanisms that operate during material deformation and stiffening make stretchability and conductivity fundamentally difficult properties to combine. The macroscale stretching of solids elongates chemical bonds, leading to the reduced overlap and delocalization of electronic orbitals. This conductivity–stretchability dilemma can be exemplified by liquid metals, in which conduction pathways are retained on large deformation but weak interatomic bonds lead to compromised strength. The best-known stretchable conductors use polymer matrices containing percolated networks of high-aspect-ratio nanometre-scale tubes or nanowires to address this dilemma to some extent. Further improvements have been achieved by using fillers (the conductive component) with increased aspect ratio, of all-metallic composition, or with specific alignment (the way the fillers are arranged in the matrix). However, the synthesis and separation of high-aspect-ratio fillers is challenging, stiffness increases with the volume content of metallic filler, and anisotropy increases with alignment. Pre-strained substrates, buckled microwires and three-dimensional microfluidic polymer networks have also been explored. Here we demonstrate stretchable conductors of polyurethane containing spherical nanoparticles deposited by either layer-by-layer assembly or vacuum-assisted flocculation. High conductivity and stretchability were observed in both composites despite the minimal aspect ratio of the nanoparticles. These materials also demonstrate the electronic tunability of mechanical properties, which arise from the dynamic self-organization of the nanoparticles under stress. A modified percolation theory incorporating the self-assembly behaviour of nanoparticles gave an excellent match with the experimental data.
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