Hypersonic phononic materials

Speaker: Prof. George Fytas
Affiliation: Max Planck Institute for Polymer Research, Mainz, Germany
Link to MSTeams meeting

Phonon propagation in architected soft materials reveals a wealth of unexpected findings not only near the Brillouin zone (BZ) but also at long wavelengths compared to the structure periodicity. The submicron fabrication enables control of the flow of acoustic waves in the GHz region that commensurate the light in the visible spectrum through opening of structure-and component related stopbands and direction dependent elasticity. The key function is the dispersion relation, ω (q) (frequency vs wave vector), which can nowadays be recorded by Brillouin light scattering (BLS) and a fraction of it by pump-probe picosecond acoustic techniques. Recent selected examples of polymer and colloid based hypersonic phononics will be presented: (i) The uniqueness of BLS for the determination of the complete elasticity of anisotropic materials utilizing both the magnitude and the vector nature of q in the linear acoustic regime of ω (q). (ii) Interference and strong resonance induced bandgaps at and below BZ and the impact of the local structure. (iii) Unexpected strong resonance-enhanced photothermal energy conversion in transparent soft opals associated to the high density of states.

[1] Z. Wang, et al “Tunable thermoelastic anisotropy in hybrid Bragg stacks with extreme polymer confinement” Angew. Chem.Int.Ed. 2020,59,1286;
[2] W. Cheng et al. ”Observation and tuning of hypersonic bandgaps in colloidal crystals” Nat.Mater. 2006, 5, 830 and T. Still et al “Simultaneous Occurrence of Structure-Directed and Particle-Resonance-Induced Phononic Gaps in Colloidal Films” Phys.Rev.Lett. 2008, 100, 194301;
[3] Alonso-Redondo, E.et al “A new class of tunable hypersonic phononic crystals based on polymer-tethered colloids” Nat.Comm. 2015, 6 8309;
[4] Y. Cang et al “Unexpected Strong Resonance-Enhanced Photothermal Energy Conversion in Transparent Soft Opals” Adv.Mater. 2021 doi.org/10.1002/adma.202170013

Seminar language: English
Chairman: Prof. Jarosław W. Kłos