Phonons are the quanta of the acoustic field and can be considered as vibrational energy and information carriers. Structured materials that can manipulate the flow of elastic energy are termed phononics, in analogy to the control of light by photonic crystals. 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 development of microfabrication techniques 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 triggering applications in optomechanics and telecommunications. The key function in phononics 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 harnessing one-component hybrid materials exemplified by polymer grafted (inorganic core) nanoparticles (GNP). GNPs combine strong vibration resonant core (size and elasticity) and transformative polymer conformation depending on physical (graft length, grafting density) parameters. Scrutinizing structure-controlled mechanics and metamaterial behavior helps establish a reliable predictive power that will open new application pathways of soft-matter-based high-frequency phononics.
George Fytas is affiliated member of IESL/FORTH and External Member of the Max Planck Institute for Polymer Research in Mainz. He has received the BS in Chemistry Department of the University of Athens and the PhD with from the Technical University of Hannover in Germany. He performed his postdoc research in SUNY at Stony Brook in USA and received his habilitation from the University of Bielefeld in Germany. George Fytas trained 32 PhD students and 16 postdocs who all have successful carriers worldwide. He has received a large number of awards and distinctions, among which he was awarded with an ERC Advanced Grant in 2015. His mission is the basic understanding and prediction of the behavior and tunability of unconventional physical properties of structured soft materials with spatiotemporal complexity.
Hosted by Juan Sebastián Reparaz, ICMAB-CSIC