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Topological carnival: Electrically-powered motions of toron crystallites in chiral liquid crystals

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arXiv 2020年

作者： Sohn, Hayley R.O. Smalyukh, Ivan I. Department of Physics and Materials Science and Engineering Program University of Colorado BoulderCO80309 United States Department of Electrical Computer and Energy Engineering and Soft Materials Research Center University of Colorado BoulderCO80309 United States Renewable and Sustainable Energy Institute National Renewable Energy Laboratory University of Colorado BoulderCO80309 United States

Malleability of metals is an example of how dynamics of defects like dislocations induced by external stresses alters material properties and enables technological applications. However, these defects move merely to comply with the mechanical forces applied on macroscopic scales whereas the molecular and atomic building blocks behave like rigid particles. Here we demonstrate how motions of crystallites and defects between them can arise within the soft matter medium in an oscillating electric field applied to a chiral liquid crystal with polycrystalline quasi-hexagonal arrangements of self-assembled topological solitons called "torons". Periodic oscillations of electric field applied perpendicular to the plane of hexagonal lattices prompt repetitive shear-like deformations of the solitons, which synchronize the electrically-powered self-shearing directions. The temporal evolution of deformations upon turning voltage on and off is not invariant upon reversal of time, prompting lateral translations of the crystallites of torons within quasi-hexagonal periodically deformed lattices. We probe how these motions depend on voltage and frequency of oscillating field applied in an experimental geometry resembling that of liquid crystal displays. We study the inter-relations between synchronized deformations of the soft solitonic particles and their arrays and the ensuing dynamics and giant number fluctuations mediated by motions of crystallites, 5-7 defects pairs and grain boundaries in the orderly organizations of solitons. We discuss how our findings may lead to technological and fundamental science applications of dynamic self-assemblies of topologically protected but highly deformable particle-like solitons. Copyright © 2020, The Authors. All rights reserved.

关键词： Self assembly

Imaging of director fields in liquid crystals using stimulated Raman scattering microscopy

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arXiv 2017年

作者： Lee, Taewoo Mundoor, Haridas Gann, Derek G. Callahan, Timothy J. Smalyukh, Ivan I. Department of Physics Liquid Crystal Materials Research Center University of Colorado BoulderCO80309 United States Department of Electrical Computer and Energy Engineering and Materials Science Engineering Program University of Colorado BoulderCO80309 United States Renewable and Sustainable Energy Institute National Renewable Energy Laboratory University of Colorado BoulderCO80309 United States

We demonstrate an approach for background-free three-dimensional imaging of director fields in liquid crystals using stimulated Raman scattering microscopy. This imaging technique is implemented using a single femtosecond pulsed laser and a photonic crystal fiber, providing Stokes and pump frequencies needed to access Raman shifts of different chemical bonds of molecules and allowing for chemically selective and broadband imaging of both pristine liquid crystals and composite materials. Using examples of model three-dimensional structures of director fields, we show that the described technique is a powerful tool for mapping of long-range molecular orientation patterns in soft matter via polarized chemical-selective imaging. Copyright © 2017, The Authors. All rights reserved.

关键词： Liquid crystals

Mass transfer study of phenolic compound liquid-liquid extraction process from bio-oil of coffee shell pyrolysis product

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materials Today: Proceedings 2023年

作者： Fardhyanti, Dewi Selvia Kadarwati, Sri Hadiyanto Fatriasari, Widya Prasetiawan, Haniif Chemical Engineering Department Faculty of Engineering Universitas Negeri Semarang Kampus Sekaran Gunungpati 50229 Indonesia Department of Chemistry Faculty of Mathematics and Natural Science Universitas Negeri Semarang 50229 Indonesia Center of Biomass and Renewable Energy Department of Chemical Engineering Diponegoro University Jl. Prof. Soedarto SH Tembalang Semarang 50275 Indonesia Graduate Program of Environmental Science School of Postgraduate Studies Diponegoro University Jl. Imam Bardjo SH Semarang Indonesia Chemical Engineering Department Faculty of Engineering Diponegoro University Semarang Indonesia Jl Raya Bogor KM 46 Cibinong 16911 Indonesia

Coffee shells are one of the potential renewable materials used in the pyrolysis process to produce bio-oil. However, the amount of phenolic compounds, which is roughly 36.74%, is one of the primary drawbacks of using coffee shell bio-oil as a fuel source. Only a little amount of research has been done on the mass transfer modeling and phenomena of phenol extraction from coffee shell bio-oil. The objectives of this study are to identify the best extraction circumstances, ascertain the empirical correlation of total mass transfer, and produce the empirical correlation of Sherwood number, which can be used to characterize the role of variables in this mass transfer process. The ratio of impeller diameter to tank diameter and the Sherwood number, as well as Reynolds, Schmidt, Weber, dispersed phase holdup, were studied as dimensionless numbers. This study used liquid-liquid extraction process at the temperature of 50 °C, with chloroform-methanol 80% as a solvent with ratio of 2:1 v/v and use bio-oil to solvent ratio of 1:1 v/v. The extraction time has an interval of 30 min (20, 50, 80, 110 min), with varied impeller diameter (3.5 cm and 4 cm), vessels diameter (9 cm and 10 cm) and mixing speed (250 rpm, 300 rpm, 350 rpm). According to the findings, the greatest phenol yield was obtained at impeller diameter 3.5 cm, tank diameter 9 cm, and mixing speed 300 rpm, with a distribution coefficient of 0.848. The results demonstrate that the maximum overall mass transfer coefficient is 4.096 × 10-4 m/s and that the liquid diffusivity is 1.7965 × 10-9 m2/s. The equation model from this study could be applied to a liquid-liquid extraction process that is scaled up to extract more phenolic compounds from the the produced bio-oil. © 2023 Elsevier Ltd. All rights reserved.

关键词： Mass transfer

Incommensurate spin correlations induced by magnetic Fe ions substituted into overdoped Bi1.75Pb0.35Sr1.90CuO6+z

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Physical Review B 2010年第14期81卷 144501-144501页

作者： H. Hiraka Y. Hayashi S. Wakimoto M. Takeda K. Kakurai T. Adachi Y. Koike I. Yamada M. Miyazaki M. Hiraishi S. Takeshita A. Kohda R. Kadono J. M. Tranquada K. Yamada Institute for Materials Research Tohoku University Sendai 980-8577 Japan Quantum Beam Science Directorate Japan Atomic Energy Agency Tokai Ibaraki 319-1195 Japan Department of Applied Physics Tohoku University Sendai 980-8578 Japan Graduate School of Science and Engineering Ehime University Matsuyama 790-8577 Japan Department of Materials Structure Science The Graduate University for Advanced Studies Tsukuba Ibaraki 305-0801 Japan Institute for Materials Structure Science High Energy Accelerator Research Organization Tsukuba Ibaraki 3005-0801 Japan Condensed Matter Physics & Materials Science Department Brookhaven National Laboratory Upton New York 11973-5000 USA WPI Research Center Advanced Institute for Materials Research Tohoku University Sendai 980-8577 Japan

Spin correlations in the overdoped region of Bi1.75Pb0.35Sr1.90CuO6+z have been explored with Fe-doped single crystals characterized by neutron scattering, muon-spin-rotation spectroscopy, and magnetic-susceptibility measurements. Static incommensurate spin correlations induced by the Fe spins are revealed by elastic neutron scattering. The resultant incommensurability δ is unexpectedly large (∼0.2 r.l.u.), as compared with δ∼1/8 in overdoped superconductor La2−xSrxCuO4. Intriguingly, the large δ in this overdoped region is close to the hole concentration p. This result is reminiscent of the δ≈p trend observed in underdoped La2−xSrxCuO4; however, it is inconsistent with the saturation of δ in the latter compound in the overdoped regime. While our findings in Fe-doped Bi1.75Pb0.35Sr1.90CuO6+z support the commonality of incommensurate spin correlations in high-Tc cuprate superconductors, they also suggest that the magnetic response might be dominated by a distinct mechanism in the overdoped region.

关键词： Incommensurate correlations substituted Substituted Spin Hole concentration Oxide superconductors Iron magnetic response Neutron scattering

Hopf solitons in helical and conical backgrounds of chiral magnetic solids

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arXiv 2020年

作者： Voinescu, Robert Tai, Jung-Shen B. Smalyukh, Ivan I. Department of Physics University of Colorado BoulderCO80309 United States Materials Science and Engineering Program Soft Materials Research Center Department of Electrical Computer and Energy Engineering University of Colorado BoulderCO80309 United States Renewable and Sustainable Energy Institute National Renewable Energy Laboratory University of Colorado BoulderCO80309 United States

Three-dimensional topological solitons attract a great deal of interest in fields ranging from particle physics to cosmology but remain experimentally elusive in solid-state magnets. Here we numerically predict magnetic heliknotons, an embodiment of such nonzero-Hopf-index solitons localized in all spatial dimensions while embedded in a helical or conical background of chiral magnets. We describe conditions under which heliknotons emerge as metastable or ground-state localized nonsingular structures with fascinating knots of magnetization field in widely studied materials. We demonstrate magnetic control of three-dimensional spatial positions of such solitons, as well as show how they interact to form molecule-like clusters and possibly even crystalline phases comprising three-dimensional lattices of such solitons with both orientational and positional order. Finally, we discuss both fundamental importance and potential technological utility of magnetic heliknotons. Copyright © 2020, The Authors. All rights reserved.

关键词： Solitons

Rocksalt-type PrO epitaxial thin film as a weak ferromagnetic Kondo lattice

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Physical Review B 2022年第1期105卷 014442-014442页

作者： Hirokazu Shimizu Daichi Oka Kenichi Kaminaga Daichi Saito Taku Yamamoto Nobuto Abe Noriaki Kimura Daisuke Shiga Hiroshi Kumigashira Tomoteru Fukumura Department of Chemistry Graduate School of Science Tohoku University Sendai 980-8578 Japan Advanced Institute for Materials Research (WPI-AIMR) and Core Research Cluster Tohoku University Sendai 980-8577 Japan Department of Applied Chemistry School of Engineering Tohoku University Sendai 980-8579 Japan Department of Physics Graduate School of Science Center for Low Temperature Science Tohoku University Sendai 980-8578 Japan Institute of Multidisciplinary Research for Advanced Materials Tohoku University Sendai 980-8577 Japan Photon Factory Institute of Materials Structure Science High Energy Accelerator Research Organization (KEK) Tsukuba 305-0801 Japan Center for Science and Innovation in Spintronics Organization for Advanced Studies and Center for Spintronics Research Network Tohoku University Sendai 980-8577 Japan

A unique Kondo lattice praseodymium monoxide PrO was synthesized in the form of an epitaxial thin film. The rocksalt-type PrO thin films with a 4f25d1 electronic configuration showed metallic conduction with a local resistivity minimum at 7 K as a result of the Kondo effect. In contrast to the other paramagnetic praseodymium monochalcogenides, PrO showed weak ferromagnetism below 28 K, followed by a transition to a more ferromagneticlike phase around 5 K. Emergence of the weak ferromagnetism probably originated from the enhanced 4f−4f exchange interaction by the short Pr-Pr distance. For the ferromagneticlike phase below 5 K, magnetic hysteresis of the anomalous Hall effect was significantly larger than that of magnetization, probably due to competing magnetic ordering.

关键词： Anomalous Hall effect Electrical conductivity Ferromagnetism Kondo effect Thin films Epitaxy

Self-assembled nematic colloidal motors powered by light

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arXiv 2020年

作者： Yuan, Ye Abuhaimed, Ghaneema N. Liu, Qingkun Smalyukh, Ivan I. Department of Physics University of Colorado BoulderCO80309 United States Soft Materials Research Center Materials Science and Engineering Program Department of Electrical Computer and Energy Engineering University of Colorado BoulderCO80309 United States Renewable and Sustainable Energy Institute National Renewable Energy Laboratory University of Colorado BoulderCO80309 United States

Biological motors are marvels of nature that inspire creation of their synthetic counterparts with comparable nanoscale dimensions, high efficiency and diverse functions. Molecular motors have been synthesized, but obtaining nanomotors though self-assembly remains challenging. Here we describe a self-assembled colloidal motor with a repetitive light-driven rotation of transparent micro-particles immersed in a liquid crystal and powered by a continuous exposure to unstructured ~1 nW light. A monolayer of azobenzene molecules defines how the liquid crystal’s optical axis mechanically couples to the particle’s surface, as well as how they jointly rotate as the light’s polarization changes. The rotating particle twists the liquid crystal, which changes polarization of traversing light. The resulting feedback mechanism yields a continuous opto-mechanical cycle and drives the unidirectional particle spinning, with handedness and frequency robustly controlled by polarization and intensity of light. Our findings may lead to opto-mechanical devices and colloidal machines compatible with liquid crystal display technology. Copyright © 2020, The Authors. All rights reserved.

关键词： Liquid crystal displays

Acoustic Sensing for Investigating Critical Heat Flux Enhancement During Pool Boiling on Electrodeposited Copper Foams

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SSRN

SSRN 2023年

作者： Pandey, Hari Mehrabi, Hamed Williams, Amanda Mira-Hernández, Carolina Coridan, Robert Henry Hu, Han Department of Mechanical Engineering University of Arkansas FayettevilleAR72701 United States Materials Science and Engineering Program University of Arkansas FayettevilleAR72701 United States Universidad Pontificia Bolivariana Medellín Colombia Department of Chemistry and Biochemistry University of Arkansas FayettevilleAR72701 United States

Nano-engineered structured boiling surfaces have shown great promise in the improvement of heat dissipation performance in thermal management applications. Electrodeposited copper foams have attracted lots of scientific and engineering interest owing to their multi-tier structures. In this study, hierarchical copper foams with ultra-wicking properties were fabricated using cathodic deposition at different pH, including both acidic (pH 0) and basic (pH 10 and 12) solutions. Pendant droplet wicking tests and pool boiling experiments were performed to characterize the wicking flux and the critical heat flux (CHF) of the fabricated copper foams, respectively. The high-speed optical images were analyzed to examine the effect of surface wickability on bubble dynamics. The CHF enhancement mechanism in hierarchical copper foams was investigated by characterizing the acoustic emissions (AE) generated during wicking and boiling vapor dynamics. The results show that base-deposited copper foams (pH 10 and 12) yield higher wicking flux and higher boiling CHF than acid-deposited copper foam (pH 0) due to smaller dendrites and crystallites. The effect of the surface structures on bubble dynamics is probed by analyzing the maximum bubble size, bubble count, and the power and dominant frequency of vapor fraction at varying heat fluxes from high-speed videos. The results reveal no significant differences between tested surfaces (polished copper and copper foams deposited at pH 0, 10, and 12) when the heat flux is kept the same. Additionally, acoustic emissions were used to understand the CHF enhancement mechanisms in different copper foam structures. While investigating the AE data, the results show consistent acoustic signatures between wicking and boiling, that is, a smaller AE amplitude is observed for higher wicking flux and higher CHF. Initiation of CHF during pool boiling was a prime source for AE and these were recognized with AE parametric study. Combing the optical and acous

关键词： Heat flux

Electrochemical Control of Copper Foam Synthesis for Critical Heat Flux Enhancement During Boiling

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SSRN

SSRN 2023年

作者： Pandey, Hari Mehrabi, Hamed Williams, Amanda Mira-Hernández, Carolina Coridan, Robert H. Hu, Han Department of Mechanical Engineering University of Arkansas FayettevilleAR72701 United States Materials Science and Engineering Program University of Arkansas FayettevilleAR72701 United States Universidad Pontificia Bolivariana Medellín Colombia Department of Chemistry and Biochemistry University of Arkansas FayettevilleAR72701 United States

Nano-engineered structured boiling surfaces have shown great promise in the improvement of heat dissipation performance in thermal management applications. Electrodeposited copper foams have attracted lots of scientific and engineering interest owing to their multi-tier structures. In this study, hierarchical copper foams with ultra-wicking properties were fabricated using cathodic deposition at different pH, including both acidic (pH 0) and basic (pH 10 and 12) solutions. Pendant droplet wicking tests and pool boiling experiments were performed to characterize the wicking flux and the critical heat flux (CHF) of the fabricated copper foams, respectively. The results show that base deposited copper foams (pH 10 and 12) yield higher wicking flux and higher boiling CHF than acid deposited copper foam (pH 0) due to smaller dendrites and crystallites. The effect of the surface structures on bubble dynamics is probed by analyzing the maximum bubble size, bubble count, and the power and dominant frequency of vapor fraction at varying heat fluxes from high-speed videos. The results reveal no significant differences between tested surfaces (flat copper and copper foams deposited at pH 0, 10, and 12) when the heat flux is kept the same. On the other hand, acoustic emissions (AE) are used to characterize the copper foam structures in both wicking and boiling tests. The results show consistent acoustic signatures between wicking and boiling that smaller AE amplitude is observed for higher wicking flux and higher CHF. Combing the optical and acoustic analysis, it is concluded that the main role of surface structures play in CHF enhancement is through improving capillary wicking underneath the bubbles rather than affecting the dynamics of the apparent liquid-vapor interfaces. This study not only explores the relationship between electrochemical control and wicking properties but also demonstrates the role of wicking in structure-enhanced boiling CHF through acoustic emission ana

关键词： Heat flux