High Frequency Acoustics in Colloid-Based Meso- And Nanostructures by Spontaneous Brillouin Light Scattering

ISBN-13: 9783642264214 / Angielski / Miękka / 2012 / 144 str.

Tim Still

Opis

Materials that can mold the ?ow of elastic waves of certain energy in certain directions are called phononic materials. The present thesis deals essentially with such phononic systems, which are structured in the mesoscale (1 lm), and with their individual components. Such systems show interesting phononic properties in the hypersonic region, i.e., at frequencies in the GHz range. It is shown that colloidal systems are excellent model systems for the realization of such phononic materials. Therefore, different structures and particle architectures are investigated by Brillouin light scattering, the inelastic scattering of light by phonons. Both the mechanical properties of the individual colloidal particles, which manifest in their resonance vibrations (eigenmodes), as well as the acoustic propagation in colloidal structures have been investigated. The measurement of the eigenmodes allows for new insights into physical properties at the mesoscale, e.g., con?nement effects, copolymer behavior, or the non-destructive determination of nanomechanical properties of core-shell particles, supporting the working groups aim to achieve a deeper understanding of 'soft mechanics' at small length scales. Another novel contribution assigned to this thesis is the ?rst experimental rea- zation of a phononic band gap arising from the interaction of these particle - genmodes with the effective medium band (hybridization gap). This ?nding already gave new impulses to the whole ?eld of phononics.

Spis treści

Basics and Brillouin Light Scattering.- Methods.- The Vibrations of Individual Colloids.- Phononic Behavior of Colloidal Systems.- Smaller than Colloids: Characterization of Stable Organic Glass.- Concluding Remarks.- Appendix: Scattering Geometry.

Blurb

The present thesis deals with the exploration of phononic properties of meso- and nanostructured colloid-based composite materials at hypersonic (GHz) frequencies. The emerging field of phononics, the mechanical analogue of photonics, treats the propagation and manipulation of acoustic waves in structured materials. Due to their widely tunable properties (size, density, etc.) and their ability to self-assembly, polymer colloids are ideal systems to realize hypersonic phononics, which are investigated by Brillouin light scattering herein. Therefore, both the mechanical and physical properties of the individual colloidal particles, which manifest in their resonance vibrations (eigenmodes), as well as the acoustic propagation in colloidal structures have been investigated.