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  1. Article ; Online: Tunable Hypersonic Bandgap Formation in Anisotropic Crystals of Dumbbell Nanoparticles.

    Kim, Hojin / Gueddida, Abdellatif / Wang, Zuyuan / Djafari-Rouhani, Bahram / Fytas, George / Furst, Eric M

    ACS nano

    2023  Volume 17, Issue 19, Page(s) 19224–19231

    Abstract: Phononic materials exhibit mechanical properties that alter the propagation of acoustic waves and are widely useful for metamaterials. To fabricate acoustic materials with phononic bandgaps, colloidal nanoparticles and their assemblies allow access to ... ...

    Abstract Phononic materials exhibit mechanical properties that alter the propagation of acoustic waves and are widely useful for metamaterials. To fabricate acoustic materials with phononic bandgaps, colloidal nanoparticles and their assemblies allow access to various crystallinities in the submicrometer scale. We fabricated anisotropic crystals with dumbbell-shaped nanoparticles via field-directed self-assembly. Brillouin light spectroscopy detected the formation of direction-dependent hypersonic phononic bandgaps that scale with the lattice parameters. In addition, the local resonances of the constituent nanoparticles enable metamaterial behavior by opening hybridization gaps in disordered structures. Unexpectedly, this bandgap frequency is robust to changes in the dumbbell aspect ratio. Overall, this study provides a structure-property relationship for designing anisotropic phononic materials with targeted phononic bandgaps.
    Language English
    Publishing date 2023-09-27
    Publishing country United States
    Document type Journal Article
    ISSN 1936-086X
    ISSN (online) 1936-086X
    DOI 10.1021/acsnano.3c05750
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Architecture Controls Phonon Propagation in All-Solid Brush Colloid Metamaterials.

    Cang, Yu / Sainidou, Rebecca / Rembert, Pascal / Matyjaszewski, Krzysztof / Bockstaller, Michael / Graczykowski, Bartlomiej / Fytas, George

    Small (Weinheim an der Bergstrasse, Germany)

    2023  Volume 20, Issue 13, Page(s) e2304157

    Abstract: Brillouin light scattering and elastodynamic theory are concurrently used to determine and interpret the hypersonic phonon dispersion relations in brush particle solids as a function of the grafting density with perspectives in optomechanics, heat ... ...

    Abstract Brillouin light scattering and elastodynamic theory are concurrently used to determine and interpret the hypersonic phonon dispersion relations in brush particle solids as a function of the grafting density with perspectives in optomechanics, heat management, and materials metrology. In the limit of sparse grafting density, the phonon dispersion relations bear similarity to polymer-embedded colloidal assembly structures in which phonon dispersion can be rationalized on the basis of perfect boundary conditions, i.e., isotropic stiffness transitions across the particle interface. In contrast, for dense brush assemblies, more complex dispersion characteristics are observed that imply anisotropic stiffness transition across the particle/polymer interface. This provides direct experimental validation of phonon propagation changes associated with chain conformational transitions in dense particle brush materials. A scaling relation between interface tangential stiffness and crowding of polymer tethers is derived that provides a guideline for chemists to design brush particle materials with tailored phononic dispersion characteristics. The results emphasize the role of interfaces in composite materials systems. Given the fundamental relevance of phonon dispersion to material properties such as thermal transport or mechanical properties, it is also envisioned that the results will spur the development of novel functional hybrid materials.
    Language English
    Publishing date 2023-11-16
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 2168935-0
    ISSN 1613-6829 ; 1613-6810
    ISSN (online) 1613-6829
    ISSN 1613-6810
    DOI 10.1002/smll.202304157
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article: Why the Relaxation Times of Polymers from Brillouin Light Spectroscopy Are Much Shorter than the Primary α-Relaxation Times

    Ngai, K. L / Fytas, George

    Macromolecules. 2019 Oct. 28, v. 52, no. 21

    2019  

    Abstract: Brillouin light spectroscopy (BLS) of polymers recorded much shorter relaxation times over the same temperature range than those obtained from other spectroscopies, including dielectric relaxation, dynamic light scattering, depolarized Rayleigh ... ...

    Abstract Brillouin light spectroscopy (BLS) of polymers recorded much shorter relaxation times over the same temperature range than those obtained from other spectroscopies, including dielectric relaxation, dynamic light scattering, depolarized Rayleigh scattering, NMR, and molecular dynamics simulations. This is an anomaly because a priori BLS is thought to monitor the structural α-relaxation of polymers like all the other techniques. First noted in 1977, the anomaly was repeatedly confirmed, but it has not been explained, and it remains a puzzling finding in amorphous polymers. In this paper, we explain this longstanding anomaly by the Coupling Model (CM), in conjunction with the fact that the α-relaxation of polymers is nonexponential at the relatively high temperatures of BLS measurements. The CM has the primitive relaxation, which is part of the Johari–Goldstein (JG) β-relaxation, and the precursor of the structural α-relaxation. The calculated primitive relaxation times match the BLS relaxation times quantitatively. This indicates that the primitive relaxation together with the JG β-relaxation of polymers is responsible for the phonon dispersion at hypersonic (GHz) frequencies, whereas the other spectroscopies probe mainly the α-relaxation. Additional support comes from the quasielastic neutron scattering experiment in the same polymer in which the primitive relaxation/JG β relaxation was directly observed with relaxation times in agreement with the calculated ones as well as the BLS relaxation times. Thus, the longstanding anomaly of polymers observed by BLS now has an explanation.
    Keywords light scattering ; molecular dynamics ; neutron diffraction ; nuclear magnetic resonance spectroscopy ; polymers ; simulation models ; temperature
    Language English
    Dates of publication 2019-1028
    Size p. 8305-8311.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 1491942-4
    ISSN 1520-5835 ; 0024-9297
    ISSN (online) 1520-5835
    ISSN 0024-9297
    DOI 10.1021/acs.macromol.9b01849
    Database NAL-Catalogue (AGRICOLA)

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  4. Article: Flash Brillouin Scattering: A Confocal Technique for Measuring Glass Transitions at High Scan Rates.

    Rolle, Konrad / Butt, Hans-Jürgen / Fytas, George

    ACS photonics

    2020  Volume 8, Issue 2, Page(s) 531–539

    Abstract: Glass transition ... ...

    Abstract Glass transition temperatures
    Language English
    Publishing date 2020-12-28
    Publishing country United States
    Document type Journal Article
    ISSN 2330-4022
    ISSN 2330-4022
    DOI 10.1021/acsphotonics.0c01533
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article ; Online: Unusual High-Frequency Mechanical Properties of Polymer-Grafted Nanoparticle Melts.

    Jhalaria, Mayank / Cang, Yu / Huang, Yucheng / Benicewicz, Brian / Kumar, Sanat K / Fytas, George

    Physical review letters

    2022  Volume 128, Issue 18, Page(s) 187801

    Abstract: Brillouin light spectroscopy is used to measure the elastic moduli of spherical polymer-grafted nanoparticle (GNP) melts as a function of chain length at fixed grafting density (0.47  chains/nm^{2}) and nanoparticle radius (8 nm). While the moduli follow ...

    Abstract Brillouin light spectroscopy is used to measure the elastic moduli of spherical polymer-grafted nanoparticle (GNP) melts as a function of chain length at fixed grafting density (0.47  chains/nm^{2}) and nanoparticle radius (8 nm). While the moduli follow a rule of mixtures (Wood's law) for long chains, they display enhanced elasticity and anomalous dissipation for graft chains <100  kDa. GNP melts with long polymers at high σ have a dry zone near the GNP core, surrounded by a region where the grafts can interpenetrate with chain fragments from adjacent GNPs. We propose that the departures from Wood's law for short chains are due to the effectively larger silica volume fraction in the region where sound propagates-this is caused by the short, interpenetrated chain fragments being pushed out of the way. We thus conclude that transport mechanisms (of gas, ions, sound, thermal phonons) in GNP melts are radically different if interpenetrated chain segments can be "pushed out of the way" or not. This provides a facile new means for manipulating the properties of these materials.
    Language English
    Publishing date 2022-05-20
    Publishing country United States
    Document type Journal Article
    ZDB-ID 208853-8
    ISSN 1079-7114 ; 0031-9007
    ISSN (online) 1079-7114
    ISSN 0031-9007
    DOI 10.1103/PhysRevLett.128.187801
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Article: Intermixed Time-Dependent Self-Focusing and Defocusing Nonlinearities in Polymer Solutions.

    Bogris, Athanasios / Burger, Nikolaos A / Makris, Konstantinos G / Loppinet, Benoit / Fytas, George

    ACS photonics

    2022  Volume 9, Issue 2, Page(s) 722–728

    Abstract: Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the ... ...

    Abstract Low-power visible light can lead to spectacular nonlinear effects in soft-matter systems. The propagation of visible light through transparent solutions of certain polymers can experience either self-focusing or defocusing nonlinearity, depending on the solvent. We show how the self-focusing and defocusing responses can be captured by a nonlinear propagation model using local spatial and time-integrating responses. We realize a remarkable pattern formation in ternary solutions and model it assuming a linear combination of the self-focusing and defocusing nonlinearities in the constituent solvents. This versatile response of solutions to light irradiation may introduce a new approach for self-written waveguides and patterns.
    Language English
    Publishing date 2022-02-01
    Publishing country United States
    Document type Journal Article
    ISSN 2330-4022
    ISSN 2330-4022
    DOI 10.1021/acsphotonics.1c01917
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  7. Article ; Online: On the origin of elasticity and heat conduction anisotropy of liquid crystal elastomers at gigahertz frequencies.

    Cang, Yu / Liu, Jiaqi / Ryu, Meguya / Graczykowski, Bartlomiej / Morikawa, Junko / Yang, Shu / Fytas, George

    Nature communications

    2022  Volume 13, Issue 1, Page(s) 5248

    Abstract: Liquid crystal elastomers that offer exceptional load-deformation response at low frequencies often require consideration of the mechanical anisotropy only along the two symmetry directions. However, emerging applications operating at high frequencies ... ...

    Abstract Liquid crystal elastomers that offer exceptional load-deformation response at low frequencies often require consideration of the mechanical anisotropy only along the two symmetry directions. However, emerging applications operating at high frequencies require all five true elastic constants. Here, we utilize Brillouin light spectroscopy to obtain the engineering moduli and probe the strain dependence of the elasticity anisotropy at gigahertz frequencies. The Young's modulus anisotropy, E
    Language English
    Publishing date 2022-09-06
    Publishing country England
    Document type Journal Article
    ZDB-ID 2553671-0
    ISSN 2041-1723 ; 2041-1723
    ISSN (online) 2041-1723
    ISSN 2041-1723
    DOI 10.1038/s41467-022-32865-1
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  8. Article ; Online: Photo-elasticity of silk fibroin harnessing whispering gallery modes.

    Korakas, Nikolaos / Vurro, Davide / Tsilipakos, Odysseas / Vasileiadis, Thomas / Graczykowski, Bartlomiej / Cucinotta, Annamaria / Selleri, Stefano / Fytas, George / Iannotta, Salvatore / Pissadakis, Stavros

    Scientific reports

    2023  Volume 13, Issue 1, Page(s) 9750

    Abstract: Silk fibroin is an important biomaterial for photonic devices in wearable systems. The functionality of such devices is inherently influenced by the stimulation from elastic deformations, which are mutually coupled through photo-elasticity. Here, we ... ...

    Abstract Silk fibroin is an important biomaterial for photonic devices in wearable systems. The functionality of such devices is inherently influenced by the stimulation from elastic deformations, which are mutually coupled through photo-elasticity. Here, we investigate the photo-elasticity of silk fibroin employing optical whispering gallery mode resonation of light at the wavelength of 1550 nm. The fabricated amorphous (Silk I) and thermally-annealed semi-crystalline structure (Silk II) silk fibroin thin film cavities display typical Q-factors of about 1.6 × 10
    MeSH term(s) Fibroins/chemistry ; Silk/chemistry ; Elastic Modulus ; Biocompatible Materials ; Optics and Photonics
    Chemical Substances Fibroins (9007-76-5) ; Silk ; Biocompatible Materials
    Language English
    Publishing date 2023-06-16
    Publishing country England
    Document type Journal Article
    ZDB-ID 2615211-3
    ISSN 2045-2322 ; 2045-2322
    ISSN (online) 2045-2322
    ISSN 2045-2322
    DOI 10.1038/s41598-023-36400-0
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  9. Article ; Online: Network Viscoelasticity from Brillouin Spectroscopy.

    Rodríguez-López, Raymundo / Wang, Zuyuan / Oda, Haruka / Erdi, Metecan / Kofinas, Peter / Fytas, George / Scarcelli, Giuliano

    Biomacromolecules

    2023  Volume 25, Issue 2, Page(s) 955–963

    Abstract: Even though the physical nature of shear and longitudinal moduli are different, empirical correlations between them have been reported in several biological systems. This correlation is of fundamental interest and immense practical value in biomedicine ... ...

    Abstract Even though the physical nature of shear and longitudinal moduli are different, empirical correlations between them have been reported in several biological systems. This correlation is of fundamental interest and immense practical value in biomedicine due to the importance of the shear modulus and the possibility to map the longitudinal modulus at high-resolution with all-optical spectroscopy. We investigate the origin of such a correlation in hydrogels. We hypothesize that both moduli are influenced in the same direction by underlying physicochemical properties, which leads to the observed material-dependent correlation. Matching theoretical models with experimental data, we quantify the scenarios in which the correlation holds. For polymerized hydrogels, a correlation was found across different hydrogels through a common dependence on the effective polymer volume fraction. For hydrogels swollen to equilibrium, the correlation is valid only within a given hydrogel system, as the moduli are found to have different scalings on the swelling ratio. The observed correlation allows one to extract one modulus from another in relevant scenarios.
    MeSH term(s) Hydrogels/chemistry ; Polymers/chemistry ; Spectrum Analysis ; Models, Theoretical ; Viscosity
    Chemical Substances Hydrogels ; Polymers
    Language English
    Publishing date 2023-12-29
    Publishing country United States
    Document type Journal Article
    ISSN 1526-4602
    ISSN (online) 1526-4602
    DOI 10.1021/acs.biomac.3c01073
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article ; Online: Free Standing Dry and Stable Nanoporous Polymer Films Made through Mechanical Deformation.

    Hsu, Hsiao-Ping / Singh, Manjesh K / Cang, Yu / Thérien-Aubin, Héloïse / Mezger, Markus / Berger, Rüdiger / Lieberwirth, Ingo / Fytas, George / Kremer, Kurt

    Advanced science (Weinheim, Baden-Wurttemberg, Germany)

    2023  Volume 10, Issue 18, Page(s) e2207472

    Abstract: A new straight forward approach to create nanoporous polymer membranes with well defined average pore diameters is presented. The method is based on fast mechanical deformation of highly entangled polymer films at high temperatures and a subsequent ... ...

    Abstract A new straight forward approach to create nanoporous polymer membranes with well defined average pore diameters is presented. The method is based on fast mechanical deformation of highly entangled polymer films at high temperatures and a subsequent quench far below the glass transition temperature T
    MeSH term(s) Polymers/chemistry ; Nanopores ; Polystyrenes/chemistry ; Temperature ; Hot Temperature
    Chemical Substances Polymers ; Polystyrenes
    Language English
    Publishing date 2023-04-25
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 2808093-2
    ISSN 2198-3844 ; 2198-3844
    ISSN (online) 2198-3844
    ISSN 2198-3844
    DOI 10.1002/advs.202207472
    Database MEDical Literature Analysis and Retrieval System OnLINE

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