The “Music” of Core−Shell Spheres and Hollow Capsules: Influence of the Architecture on the Mechanical Properties at the Nanoscale

• Published in: Nano letters 2008-10, Vol.8 (10), p.3194-3199
• Main Authors: Still, T, Sainidou, R, Retsch, M, Jonas, U, Spahn, P, Hellmann, G. P, Fytas, G
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Low-dimensional structures (superlattices, quantum well structures, multilayers): structure, and nonelectronic properties; Mechanical and acoustical properties of condensed matter; Mechanical properties of nanoscale materials; Physics; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties)
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl801500n

We report on the first measurement of elastic vibrational modes in core−shell spheres (silica−poly(methyl methacrylate), SiO2−PMMA) and corresponding spherical hollow capsules (PMMA) with different particle size and shell thickness using Brillouin light scattering, supported by numerical calculations. These localized modes allow access to the mechanical moduli down to a few tens of nanometers. We observe reduced mechanical strength of the porous silica core, and for the core−shell spheres a striking increase of the moduli in both the SiO2 core and the PMMA shell. The peculiar behavior of the vibrational modes in the hollow capsules is attributed to antagonistic dependence on overall size and layer thickness in agreement with theoretical predictions.