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Smartphon Report Summary

Project ID: 694977
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - Smartphon (Small - and nano - scale soft phononics)

Reporting period: 2016-09-01 to 2018-02-28

Summary of the context and overall objectives of the project

• What is the problem/issue being addressed?
The propagation of elastic waves (acoustic waves or phonons) in architected matter is a generic problem that impacts many areas of material science. Phonon propagation in structure composite structures depends on many interrelated parameters (four for each solid component). This number increases further when anisotropy is introduced in the design of the structures. Besides the structural and elastic parameters, phononic behavior is further influenced by additional factors such as complex structural relaxation, confinement and interfacial effects. There is therefore rich unexplored and hardly predictable fundamental science that needs a supporting foundation to be established. The key quantity is the dispersion relation ω(k), that relates the frequency ω and the wave vector k of the propagating wave, in the composite matter. Engineering of ω(k) to allow propagation only on desired frequencies , polarizations and directions (metamaterials) requires control of both structure periodicity and component dimensions and elastic properties. Extension to high frequency phononics to enable simultaneous manipulation of hypersonic phonons and visible light needs organization in the submicron and nanometer scale range via self-assembly. This is a ubiquitous property of soft matter (polymers, colloids) that allows such fabrication of complex hierarchical structures with tailored and manifold functionalities.Many important questions in this young field of small-nano scale phononics are just being raised and require new conceptual and technical approaches to address them.

• Why is it important for society?
1).The advancement of a new field creates new knowledge in physics and engineering and challenges material nanofabrication. This know-how is being transferred to young scientists (PhD, Postdoc’s and visiting scholars) working in this program. 2) Mechanical properties and the stability of nanostructured materials are of paramount importance for a wide range of applications that comprise microelectronic, photonics, nano-electro-mechanical systems, nanofluidics, and biomedical technologies. Crowding, space-filling and confinement in soft condensed matter are conditions that can have severe effect on the material properties in particular at metastable states. 3) A detailed understanding of phonon propagation in soft nanostructured media is a precondition to access fundamental concepts such as heat management and phonon-photon interactions. The wastage through heat in ICT devices is estimated to be around 60% with energy consumption in the range of 100TWh (only in Germany) whereas strong opto-acoustic effect can find applications also in devices as nanoactuators. Other applications can emerge from the still unprecedented phonon-matter interactions.

• What are the overall objectives?
The project addresses challenging objectives at the frontiers of the involved research: a) Develop new capabilities for phonon management in mesoscopic soft matter. The integrated approach will generate the missing information for phonon band structure engineering as is necessary to tailor the dispersion relations for a particular application. b) Extend concepts and techniques from polymer and colloid physics into the new area of phononics. Structure and its component materials dictate the shape of the experimental phonon dispersion relations. Soft matter-based phononics utilize the main advantages of facile processing as well as architectural and topological changes of the constituent components. c) Determine cuurently unknown dimension-dependent thermo-mechanical properties. The ability to pattern substrates at the nanoscale has largely evolved as a result of advances in thin film technologies and electronics; the stability of nanostructured films is of paramount importance. d) Realize functional photonic devices based on soft matter systems. Since hPnC have lattice constants in the range of visible/near

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the first reporting period the performed work is summarized as follows:
1 Purchase of all approved equipment and hire of two PhD’s, two Postdocs and host a Humboldt Awardee and three visiting PhD’s (Spain and USA).
2. Build-up and operate a) the backscattering /transmission Brillouin light spectroscopy and b) the 3ω heat conductivity technique (project 2).
3. Fabrication and characterization of the elastic and photoelastic parameters of a periodic array of nanowalls (gratings) (project 1,2, Fig.3d).
4a. Synthesis/characterization of core/shell polymer colloids (project 1) and record the vibration spectrum at different temperatures through the glass transition (project 2). 4b. Thermomechanical behavior of polymer-tethered silica particles and their assembled films (project 1&2).
5.Measurement of a) heat conductivity in polymer nanocomposites (project 2) and b) thermomechanical properties of metal-polymer nanocomposites allowing specific interactions with the light (project 2,4) in collaboration with Prof.M.Retsch (ERC starting grant, University of Bayreuth).
6. Fabrication of wrinkled periodic polymer films (project 1) and record of the phonon dispersion along and normal to wrinkling periodicity (project 2).
7. Phonon propagation in biophononic hierarchical fibers: spider silk and silk worm fibers (project 2,3).
8. Response of the whispering modes of polymer spheres to unidirectional stretching, precursor experiment for optomechanical coupling (project 4)

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Over the period Sept.1,2016 to Feb. 28, 2018, the progress beyond the state-of- the-art reported in seven papers relates to :
(1) A new discovery concerning the phonon propagation in spider silk fibers (Nat. Mater. 2016, 15,1079). The hierarchical structure, the prestain and the nonlocal nonlinearity lead to unprecedented hypersonic stopband and an anomalous dispersion. In a Views & News (Nat. Mater.2016,15,1054) this explanation termed ‘dynamic” mechanics and this “discovery could drive the design of bio-inspired and biocompatible dynamic materials”.
(2) The heat conductivity- speed of sound relationship in metal oxide based polymer nanocomposites (J.Phys.Chem.C 2017,121, 25568. The dependence of heat conductivity on the sound velocity reported for amorphous polymers is not observed in this nanocomposites attributed to the increase of the phonon mean free path at high solid fraction.
(3). A counterintuitive dependence of the elastic modulus to local polymer structure in polymer-tethered colloids (Macromolecules 2017, 50, 8678). The sparsely polymer tethered systems reveal slow polymer chain dynamics and the assembled films display high modulus than would be anticipated from the effective medium (Wood’s) model.
(4) A robust phonon guiding in high aspect ratio photoresist gratings (Nanoscale 2017,9,2739 with cover image).. The phonon propagation in low and high aspect ratio nanowalls reveals differences in elastic and photoelastic properties related to the two-beam interference lithography fabrication determination of the mechanical properties in nanostructured material is of great importance of their fidelity.
(5) Application of whispering galley modes in polymer resonators detect surface birefringence (ACS Omega 2017,2, 9127 ). Contrary to the bulk glassy polystyrene, the stress -optical law coefficient is negative suggesting different segment orientation t the strain direction.
The “expected results until the end of the project” will relate to:
1. The mechanism of a new tunable optical absorption enhanced enhancement in soft opals not foreseen in the AdG and hence will be considered for an ERC proof of concepts application.
2. The establishment of the “particle vibration spectroscopy” (project 2) as a direct probe of surface mobility and interactions with great relevance to the glass transition phenomenon.
3. All four projects of this AdG.

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