The Effects of Nanoscopic Fillers on the Viscoelastic Response of Polymers
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The Effects of Nanoscopic Fillers on the Viscoelastic Response of Polymers Jean Harry Xavier*, J. Sokolov, M.H. Rafailovich, Department of Materials Science and Engineering, SUNY at Stony Brook. Stony Brook, N.Y. 11794. ABSTRACT We have used a technique developed by Brochard (Macromolecules, 2004, 37, 1470) using free standing thin films to study the viscoelastic response of filled-polymer films. Transmission Electron Microscopy (TEM) experiments reported that fillers were well distributed within the films, and therefore no clustering and interfacial segregation occurred. Results from Shear Modulation Force Microscopy (SMFM) measurements revealed that the glass transition temperature of the polymer (Tg) was depressed by 10°C relative to the bulk for Au (10 nm), and bulk like for Au (3 nm). The effects of colloidal fillers on the tracer diffusion coefficient (D) were studied using secondary ion mass spectrometry (SIMS), and results found that D was increased significantly for the Au 10 nm, and constant for the Au 3 nm. Values for zero shear rate viscosity extracted from the diffusion coefficient were compared to the shear strain calculated from the hole growth measurements, and theoretical predictions. Results were attributed to an increase in excluded volume when large particles were introduced into the matrix. * Corresponding author: Telephone: 631-632-4410, Fax: 631-632-5764, email: [email protected] INTRODUCTION The development of advanced materials from inorganic nanoparticle fillers represents actually a fast-growing area of science and technology due to the significant effect of these fillers in mechanical, dielectric, optical, and rheological properties of the polymeric materials 1,2. For most technological applications, nanoparticle fillers are commonly used in the form of thin films. Currently, such films are usually made by spincoating, spraying, or sometimes simple painting of nanoparticle-matrix mixtures 3. Previous experimental studies have been performed on the effects of filler nano-particles on the characterization of the polymer-filler interface 4 and the mechanical properties of the polymer films 5. However, less attention has been focused on the impact of fillers on the rheological properties of polymer thin films in the melt. Starr, et al 6 also found that for attractive surface interactions, slow dynamics near the surface occur, which results in an increase in viscosity and glass transition temperature (Tg). According to Jaber et al 7, for spherical fillers and size comparable to polymer radius of gyration (Rg), fillers induce orientation near the polymer surface, causing shear thinning. In this manuscript, we report observations on the effects of nanofillers on the viscoelastic response of polymer thin films using free standing films. The nanoparticles used for this project are similar to those used in the literature studies 8: 3 nm size and 10 nm Au formed by the one phase synthesis method using tetrahydrofuran (THF) as solvent 9 and functionalized with noctadecanethiol (C18H37SH
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