Synthesis and Patterning of Polymer Matrix Nanocomposites Using Femtosecond Laser-assisted Processing
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Synthesis and Patterning of Polymer Matrix Nanocomposites Using Femtosecond Laser-assisted Processing Travis J. DeJournett1 and James B. Spicer1 1 Dept. of Materials Science and Engineering, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, U.S.A. ABSTRACT We describe a scalable synthesis process for the production and patterning of polymer matrix nanocomposites (PMNCs) using femtosecond laser irradiation to target specific functional behaviors. A modified, in situ chemical vapor deposition (CVD), nanoinfusion process was used to nucleate and grow nanoparticles in the bulk of an optically transparent polytetrafluoroethylene-co-hexafluoropropylene (FEP) polymer matrix. Metallic nanoparticles synthesized with this process can have a strong optical absorption at their surface plasmon resonance (SPR) frequency and we have utilized this property to selectively irradiate and pattern nanocomposites via femtosecond, photothermal heating. If the nanoparticle environment includes species used for chemical vapor deposition, the heat causes a localized decomposition of the precursor species in the immediate vicinity of the nanoparticle leading to a variety of core-shell nanostructures. Using this processing scheme, we have grown shells of tungsten oxide around silver nanoparticles within the polymer matrix resulting in a 40 nm red shift in the SPR of the silver nanoparticles in regions of the material exposed to femtosecond laser pulses. This process has also been adapted to polymers containing tungsten oxide nanoparticles so that the photocatalytic behavior of the particles could be used to the decompose precursor species in the immediate vicinity of the irradiated nanoparticles. These results demonstrate that, by using optical masks and laser processing, it is possible to synthesize nanocomposites with a high degree of control over the location, composition, size, and distribution of nanoparticles within a polymer matrix resulting in patterned materials with tailored electrical, optical, and photocatalytic properties. INTRODUCTION Many polymer matrix nanocomposites are composed of a random distribution of nanoparticles within a solid polymer matrix. The material properties of these nanocomposites are determined by the size and type of nanofeatures, their distribution in the matrix, and their interaction with the bulk matrix material. Typically, these nanocomposites are engineered to have a specific property and are used as a coating to alter the material properties of a device or structure. They have been synthesized via CVD, thermolysis of chemical precursors, co-sputtering, evaporation, pulsed laser deposition, or by distributing nanoparticles within a liquid monomer solution that is subsequently polymerized. The polymer nanocomposites produced with these methods often result in a random distribution of nanoparticles, rods, cubes, etc. throughout the bulk of the polymer. It is desirable to be able to pattern polymer nanocomposites in order to tailor their material properties. This has recently been accompli
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