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Sökning: WFRF:(Bar Ilan Pri)

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1.
  • Ferreira Fernandes, Ricardo Manuel, et al. (författare)
  • Lateral Diffusion of Dispersing Molecules On Nanotubes As Probed by NMR
  • 2014
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:1, s. 582-589
  • Tidskriftsartikel (refereegranskat)abstract
    • Noncovalent dispersion of carbon nanotubes is essential to most applications but still poorly understood at the molecular level. The interaction of the dispersing molecule with the nanotube, wrapping or nonwrapping, still awaits consensus. Herein, we have studied by H-1 NMR diffusometry some features of molecular dynamics in the system of carbon nanotubes dispersed by triblock copolymer Pluronics F127 in water. The diffusional decays obtained at different diffusion times, Delta, are not single-exponential and have a complex Delta-dependent profile, ultimately implying that the polymer is observed in two states: free (in unimeric form) and nanotube-bound. Fitting a two-site exchange model to the data indicates that at any instant, only a small fraction of polymers are adsorbed on the nanotubes, with polydisperse residence times in the range of 100-400 ms. Most significantly, we further provide an estimate of D = (3-8) x 10(-12) m(2) s(-1) the coefficient of lateral diffusion of the polymer along the nanotube surface, which is an order of magnitude slower than the corresponding self-diffusion coefficient in water. The emerging picture is that of a nonwrapping mode for the polymer-nanotube interaction.
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2.
  • Frise, Anton, et al. (författare)
  • Polymer Binding to Carbon Nanotubes in Aqueous DispersionsStudied by NMR Diffusometry
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • The diffusion behavior of block copolymer Pluronic F-127 in aqueous dispersions of single-walled (SW) and multi-walled (MW) carbon nanotubes (CNT) has been studied by pulsed-field-gradient (PFG) 1H NMR spectroscopy. We show that the polymers are either free monomers or bound to the CNT and exchange between these two states. The residence times and relative populations in those states could also be obtained. For both classes of CNT, the residence time in the bound state was found to be similar and in the order of 10-100 milliseconds. Thermal gravimetric analysis (TGA) showed that the SWCNT concentration dispersed by F-127 was higher than that for MWCNT.
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