TECHNICAL ABSTRACTS promote the use of exposed Fe nanoparticles supported on different substrates for the growth of SWNTs, thereby utilizing some of the unique advantages offered by PECVD.[4] References: 1) Dai, H. J.; Rinzler, A. G.; Nikolaev, P.; Thess, A.; Colbert, D. T.; Smalley, R. E. Chem. Phys. Lett. 1996, 260, 471. (b) Sinnott, S. B.; Andrews, R.; Qian, D.; Rao, A. M.; Mao, Z.; Dickey, E. C.; Derbyshire, F. Chem. Phys. Lett. 1999, 315, 25. (c) Cheung C. L.; Kurtz, A.; Park, H.; Lieber, C. M. J. Phys Chem B 2002, 106, 2429. 2) Meyyappan, M.; Delzeit, L.; Cassell, A.; Hash, D. Plasma Sources Sci. Technol. 2003, 12, 205. 3) (a) Kato, T.; Jeong, G.; Hirata, T.; Hatakeyama, R.; Tohji, K.; Motomiya, K. Chem. Phys. Lett. 2003, 381, 422. (b) Kato, T.; Jeong, G.; Hirata, T.; Hatakeyama, R.; Tohji, K. Jpn. J. Appl. Phys. 2004, 43, L1278. (c) Li, Y.; Mann, D.; Rolandi, M.; Kim, W.; Ural, A.; Hung, S.; et al. Nano Lett. 2004, 4, 317. (d) Delzeit, L.; Nguyen, C. V.; Stevens, R. M.; Han, J.; Meyyappan, M. Nanotechnology 2002, 13, 280. 4) Amama, P. B.; Maschmann, M. R.; Sands, T. D.; Fisher, T. S. J. Phys. Chem. B 2006, 110, 10636.
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“Shear Flow In Entangled Polymers Investigated Using Confocal Microscopy And Particle Image Velocimetry”
Keesha A. Hayes*1, Mark R. Buckley2, Itai Cohen2 and Lynden A. Archer1 School of Chemical & Biomolecular Engineering, Cornell University, Ithaca, NY 14853 2Department of Physics, Cornell University, Ithaca, NY 14853
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Abstract We use confocal microscopy and particle image velocimetry to visualize flow of entangled polymers in a custom‐built, planar‐Couette rheometer. Polybutadiene solutions spanning a range of molecular weights (Mw=200K, 788K) and entanglement densities (8 ≤ N/ Ne ≤ 56) are seeded with 250‐300 nm particle tracers. When compared to traditional couette and cone & plate geometries, our narrow gap (~ 35 μm), small aspect ratio (as < 1/143) shear cell is a more rigorous setting for exploring banding in entangled polymers. With increasing imposed shear rate, violations of the boundary no‐slip condition become more severe and the difference between the imposed and measured shear rates increases. Despite these observations, importantly, the measured velocity profiles are generally linear, even for rates in the non‐Newtonian shear regime. This finding disagrees with recent reports that shear banding is a characteristic flow response of entangled polymers, and instead points to interfacial slip as an important source of strain loss. The measured shear rates and shear stresses are used to characterize slip. We find two slip regimes; the transition to the highly non‐linear second regime occurs at stresses comparable to the elastic modulus of the entangled polymer network. These results are consistent both with polymer slip theories and published data obtained using other techniques. 137