Pulsed laser characterization of multicomponent polymer acoustic and mechanical properties in the sub-GHz regime
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T. Pezeril Institute for Soldier Nanotechnologies, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
D.H. Torchinsky Institute for Soldier Nanotechnologies, Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
J. Yoon Institute for Soldier Nanotechnologies, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
S.E. Kooi Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
E.L. Thomas Institute for Soldier Nanotechnologies, Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
K.A. Nelsona) Institute for Soldier Nanotechnologies, Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (Received 28 September 2006; accepted 14 November 2006)
We investigated the acoustic properties in the sub-GHz frequency regime of a multilayer system comprising alternating 100-nm scale TiO2/poly(methyl methacrylate) (PMMA) layers through a laser photoacoustic method, impulsive stimulated thermal scattering (ISTS). The acoustic dispersion curves were determined, and the mechanical properties were extracted from the experimental results.
I. INTRODUCTION
The mechanical behavior of multicomponent materials that contain ordered or partially ordered domains can be markedly different from those exhibited by each individual neat component.1 This opens the possibility to optimize mechanical properties of materials for specialized applications based on the manner in which the individual components are combined and structured. Amorphous polymers such as poly(methyl methacrylate) (PMMA) and nanocrystalline materials such as titania (TiO2) are particularly attractive for many engineering applications due to their intrinsic properties including transparency, relatively high moduli, and their ease of
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0081 J. Mater. Res., Vol. 22, No. 3, Mar 2007
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processibility, which enables a wide range of systematically variable multicomponent morphologies to be produced.2,3 In multilayer systems with these components, it should be possible to control the mechanical behavior, as well as the acoustic properties including phase and group velocity dispersion and phononic and possibly phononic band gap structure, by controlling the ordering and thickness of each individual layer and/or by optimizing the number of layers.4 We have used multilayer structures of PMMA and TiO2 nanoparticles as model systems to understand the mechanical behavior of complex multilayer stacks. A better understanding of the mechanical properties of these types of systems will be used in the design of new materials for energy-dissipation applications.5 Our study involved the use of a laser photoacoustic method, impulsive stimulate
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