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2. Determination of the elastic moduli of CVD graphene by probing graphene/polymer Bragg stacks

Author

Liu, Bohai, Pavlou, Christos, Wang, Zuyuan, Cang, Yu, Galiotis, Costas, and Fytas, George

Subjects
Condensed Matter - Materials Science, Physics - Applied Physics
Abstract

Graphene has been widely used in the form of micro-flakes to fabricate composite materials with enhanced mechanical properties. Due to the small size of the inclusions and their random orientation within the matrix, the superior mechanical properties of graphene cannot be fully exploited. Recently, attempts have been made to fabricate nanolaminate composites by interleaving large sheets of chemical vapor deposition (CVD) monolayer graphene between thin layers of polymer matrices. However, CVD graphene is inevitably accompanied by wrinkles that are formed in the synthesis process, and it remains unknown how the wrinkles affect the mechanical properties of graphene. Here, we employ Brillouin Light Spectroscopy (BLS) to study the elastic moduli of CVD graphene by probing graphene/poly(methylmethacrylate) hybrid Bragg stacks at zero strain. We find the Young's and shear moduli of the CVD graphene, which has wrinkles in the form of sharp elevations of height of about 6 nm and a FWHM of ca. 30 nm, to be 680 and 290 GPa, respectively, with the former being about 30% lower than that of exfoliated, flat graphene. This work sheds light on the elastic properties of CVD graphene and provides a method that can be extended to studying the wrinkle-induced softening effect in other two-dimensional materials., Comment: Paper and Supporting Info

Published
2021
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3. Lifting restrictions on coherence loss when characterizing non-transparent hypersonic phononic crystals

Author

Rolle, Konrad, Yaremkevich, Dmytro, Scherbakov, Alexey V., Bayer, Manfred, and Fytas, George

Subjects
Physics - Optics, Condensed Matter - Materials Science, Condensed Matter - Other Condensed Matter
Abstract

Hypersonic phononic bandgap structures confine acoustic vibrations whose wavelength is commensurate with that of light, and have been studied using either time- or frequency-domain optical spectroscopy. Pulsed pump-probe lasers are the preferred instruments for characterizing periodic multilayer stacks from common vacuum deposition techniques, but the detection mechanism requires the injected sound wave to maintain coherence during propagation. Beyond acoustic Bragg mirrors, frequency-domain studies using a tandem Fabry-Perot interferometer (TFPI) find dispersions of two- and three-dimensional phononic crystals (PnCs) even for highly disordered samples, but with the caveat that PnCs must be transparent. Here, we demonstrate a hybrid technique for overcoming the limitations that time- and frequency-domain approaches exhibit separately: We inject coherent phonons into a non-transparent PnC using a pulsed laser and acquire the acoustic transmission spectrum on a TFPI, where pumped appear alongside spontaneously excited (i.e. incoherent) phonons. Choosing a metallic Bragg mirror for illustration, we determine the bandgap and compare with conventional time-domain spectroscopy, finding resolution of the hybrid approach to match that of a state-of-the-art asynchronous optical sampling setup. Thus, the hybrid pump-probe technique retains key performance features of the established one and going forward will likely be preferred for disordered samples., Comment: 18 pages, 4 figures, 54 references

Published
2021

7. Organic nanoparticles with tunable size and rigidity by hyperbranching and cross-linking using microemulsion ATRP.

Author

Rongguan Yin, Tarnsangpradit, Jirameth, Gul, Akhtar, Jaepil Jeong, Xiaolei Hu, Yuqi Zhao, Hanshu Wu, Qiqi Li, Fytas, George, Karim, Alamgir, Bockstaller, Michael R., and Matyjaszewski, Krzysztof

Subjects
POLYMERS, METHYL methacrylate, CHEMICAL properties, NANOPARTICLE size, ELASTICITY
Abstract

Unlike inorganic nanoparticles, organic nanoparticles (oNPs) offer the advantage of "interior tailorability," thereby enabling the controlled variation of physicochemical characteristics and functionalities, for example, by incorporation of diverse functional small molecules. In this study, a unique inimer-based microemulsion approach is presented to realize oNPs with enhanced control of chemical and mechanical properties by deliberate variation of the degree of hyperbranching or cross-linking. The use of anionic cosurfactants led to oNPs with superior uniformity. Benefitting from the high initiator concentration from inimer and preserved chain-end functionality during atom transfer radical polymerization (ATRP), the capability of oNPs as a multifunctional macroinitiator for the subsequent surface-initiated ATRP was demonstrated. This facilitated the synthesis of densely tethered poly(methyl methacrylate) brush oNPs. Detailed analysis revealed that exceptionally high grafting densities (~1 nm-2) were attributable to multilayer surface grafting from oNPs due to the hyperbranched macromolecular architecture. The ability to control functional attributes along with elastic properties renders this "bottom-up" synthetic strategy of macroinitiator-type oNPs a unique platform for realizing functional materials with a broad spectrum of applications. [ABSTRACT FROM AUTHOR]

Published
2024
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8. Thermomechanical Properties and Glass Dynamics of Polymer-Tethered Colloidal Particles and Films

Author

Cang, Yu, Reuss, Anna N, Lee, Jaejun, Yan, Jiajun, Zhang, Jianan, Alonso-Redondo, Elena, Sainidou, Rebecca, Rembert, Pascal, Matyjaszewski, Krzysztof, Bockstaller, Michael R, and Fytas, George

Subjects
Chemical Sciences, Engineering, Polymers
Abstract

Polymer-tethered colloidal particles (aka "particle brush materials") have attracted interest as a platform for innovative material technologies and as a model system to elucidate glass formation in complex structured media. In this contribution, Brillouin light scattering is used to sequentially evaluate the role of brush architecture on the dynamical properties of brush particles in both the individual and assembled (film) state. In the former state, the analysis reveals that brush-brush interactions as well as global chain relaxation sensitively depend on grafting density; i.e., more polymer-like behavior is observed in sparse brush systems. This is interpreted to be a consequence of more extensive chain entanglement. In contrast, the local relaxation of films does not depend on grafting density. The results highlight that relaxation processes in particle brush-based materials span a wider range of time and length scales as compared to linear chain polymers. Differentiation between relaxation on local and global scale is necessary to reveal the influence of molecular structure and connectivity on the aging behavior of these complex systems.

Published
2017

14. Photo-elasticity of silk fibroin harnessing whispering gallery modes

Author

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

Published
2023
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18. Optomechanical Hot-Spots in Metallic Nanorod–Polymer Nanocomposites

Author

Vasileiadis, Thomas, Noual, Adnane, Wang, Yuchen, Graczykowski, Bartlomiej, Djafari-Rouhani, Bahram, and Fytas, George

Subjects
Brillouin light scattering, gold nanorods, plasmons, polymers, optomechanics
Abstract

Plasmonic coupling between adjacent metallic nano-particles can be exploited for acousto-plasmonics, single-molecule sensing, and photochemistry. Light absorption or electron probes can be used to study plasmons and their interactions, but their use is challenging for disordered systems and colloids dispersed in in-sulating matrices. Here, we investigate the effect of plasmonic coupling on optomechanics with Brillouin Light Spectroscopy (BLS) in a prototypical metal-polymer nanocomposite, gold nanorods (Au NRs) in polyvinyl-alcohol. The intensity of the light inelastically scattered on thermal phonons captured by BLS is strongly affected by the wavelength of the probing light. When light is resonant with the transverse plasmons, BLS reveals mostly the normal vibrational modes of single NRs. For lower energy off-resonant light, BLS is dominated by coupled bending modes of NR dimers. The experimental results, supported by optomechanical calculations, document plasmonically enhanced BLS and reveal energy-dependent confinement of coupled plasmons close to the tips of NR dimers, generating BLS hot-spots. Our work paves the way for establishing BLS as an optomechanical probe of plasmons and promotes nanorod-soft matter nanocomposites for acousto-plasmonics. This project has received funding from the European Union’s Hori-zon 2020 research and innovation programme under the Marie Skłodowska-Curie Action Grant Agreement 101003436

Published
2023

24. Harnessing polymer grafting to control the shape of plasmonic nanoparticles.

Author

Zhou, Ying, Yan, Liting, Maji, Tanmoy, Lévêque, Gaëtan, Gkikas, Manos, and Fytas, George

Subjects
GRAFT copolymers, SURFACE plasmon resonance, POLYMERIC nanocomposites, LIGHT scattering, MOLECULAR weights, SURFACE plasmons, IMPACT craters
Abstract

Matrix-free polymer grafted nanoparticles (NPs) are single component polymer nanocomposites (PNCs) for which the often reported severe aggregation of the conventional PNCs can be suppressed. For a given particle core, the size and shape of the polymer grafted nanoparticles can be controlled by the molecular weight of the polymer and its grafting density. However, the degree of homogeneity of one-component PNCs depends on the grafted chain molecular weight and grafting density, as well as on the shape of grafted NPs. Surface plasmon resonance enhanced dynamic light scattering from very dilute solutions, yielding both translational and rotational transport coefficients, complemented by UV–Vis extinction spectra, can detect deviations from spheres. Here, we report that poly(isobutylene)-grafted Ag NPs strongly deviate from the spherical shape and are modeled as prolate spheroids. This NP asphericity, due to inhomogeneous grafting, can impact the structure and properties of plasmonic PNCs in the solid state. Thus, characterizing this behavior is a crucial step prior to the formation of one-component PNCs. [ABSTRACT FROM AUTHOR]

Published
2020
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27. Nanoscale-Structured Hybrid Bragg Stacks with Orientation-and Composition-Dependent Mechanical and Thermal Transport Properties

Author

Dörres, Theresa, Bartkiewicz, Malgorzata, Herrmann, Kai, Schöttle, Marius, Wagner, Daniel, Wang, Zuyuan, Ikkala, Olli, Retsch, Markus, Fytas, George, Breu, Josef, University of Bayreuth, Max Planck Institute for Polymer Research, University of Electronic Science and Technology of China, Department of Applied Physics, Aalto-yliopisto, and Aalto University

Subjects
organic-inorganic nanocomposites, thermal conductivity, mechanical tensor, Brillouin light spectroscopy, nacre mimetic
Abstract

openaire: EC/H2020/742829/EU//DRIVEN Funding Information: This work was supported by the German Science Foundation within the Collaborative Research Projects SFB 840 and SFB 1357. Z.W. and G.F. acknowledge financial support by ERC AdG SmartPhon (Grant 694977), and O.I. acknowledges ERC AdG Driven (Grant 742829) and an Alexander von Humboldt Research Award. Open access funded by Max Planck Society. Publisher Copyright: © 2022 American Chemical Society. Layered nanomaterials fascinate researchers for their mechanical, barrier, optical, and transport properties. Nacre is a biological example thereof, combining excellent mechanical properties by aligned submicron inorganic platelets and nanoscale proteinic interlayers. Mimicking nacre with advanced nanosheets requires ultraconfined organic layers aimed at nacre-like high reinforcement fractions. We describe inorganic/polymer hybrid Bragg stacks with one or two fluorohectorite clay layers alternating with one or two poly(ethylene glycol) layers. As indicated by X-ray diffraction, perfect one-dimensional crystallinity allows for homogeneous single-phase materials with up to a 84% clay volume fraction. Brillouin light spectroscopy allows the exploration of ultimate mechanical moduli without disturbance by flaws, suggesting an unprecedentedly high Young's modulus of 162 GPa along the aligned clays, indicating almost ideal reinforcement under these conditions. Importantly, low heat conductivity is observed across films, κ⊥ = 0.11-0.15 W m-1 K-1, with a high anisotropy of κ||/κ⊥ = 28-33. The macroscopic mechanical properties show ductile-to-brittle change with an increase in the clay volume fraction from 54% to 70%. Conceptually, this work reveals the ultimate elastic and thermal properties of aligned layered clay nanocomposites in flaw-tolerant conditions.

Published
2022

28. Nanoscale-Structured Hybrid Bragg Stacks with Orientation- and Composition-Dependent Mechanical and Thermal Transport Properties: Implications for Nacre Mimetics and Heat Management Applications

Author

Dörres, Theresa, primary, Bartkiewicz, Malgorzata, additional, Herrmann, Kai, additional, Schöttle, Marius, additional, Wagner, Daniel, additional, Wang, Zuyuan, additional, Ikkala, Olli, additional, Retsch, Markus, additional, Fytas, George, additional, and Breu, Josef, additional

Published
2022
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33. Fast Light-Driven Motion of Polydopamine Nanomembranes

Author

Vasileiadis, Thomas, primary, Marchesi D’Alvise, Tommaso, additional, Saak, Clara-Magdalena, additional, Pochylski, Mikolaj, additional, Harvey, Sean, additional, Synatschke, Christopher V., additional, Gapinski, Jacek, additional, Fytas, George, additional, Backus, Ellen H. G., additional, Weil, Tanja, additional, and Graczykowski, Bartlomiej, additional

Published
2021
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49. Stepwise noncovalent synthesis leading to dendrimer-based assemblies in water

Author

Hermans, Thomas M., Broeren, Maarten A.C., Gomopoulos, Nikos, Smeijers, A.F., Mezari, Brahim, Van Leeuwen, Ellen N.M., Vos, Matthijn R.J., Magusin, Pieter C.M.M., Hilbers, Peter A.J., Van Genderen, Marcel H.P., Sommerdijk, Nico A.J.M., Fytas, George, and Meijer, E.W.

Subjects
Dendrimers -- Research, Chloroform -- Usage, Chloroform -- Chemical properties, Chemistry
Abstract

A step-wise noncovalent synthetic procedure involving a preassembly step in chloroform is used to obtain dendrimer-based guest-host assemblies in water. The concepts of stepwise noncovalent synthesis have provided valuable tools for obtaining new supramolecular assemblies.

Published
2007

50. Multicomponent host-guest chemistry of carboxylic acid and phosphonic acid based guests with dendritic hosts: An NMR study

Author

Broeren, Maarten A. C., Meijer, E. W., de Waal, Bas F. M., van Genederen, Marcel H. P., Sanders, H. M. H. F., and Fytas, George

Subjects
Dendrimers -- Research, Phosphoric acid -- Chemical properties, Nuclear magnetic resonance spectroscopy -- Usage, Carboxylic acids -- Chemical properties, Chemistry
Abstract

A new methodology is introduced to get insights in the binding of carboxylic and phosphoric acid type guest molecules to dendrimers by making use of (super 13)C NMR and (super 31)P NMR. The method is applicable for any type of guest and host in chloroform and gives information about binding strength, binding stoichiometry and binding dynamics.

Published
2005

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