Single-walled carbon nanotubes (SWNTs) are dispersed in water via wrapping with short segments of single-stranded DNA (ssDNA). Small angle neutron scattering suggests a power-law exponent that is consistent with clustered nanotubes and hence marginal stability. The SWNT-ssDNA complex is used to stabilize dispersions of hydrophilic colloidal particles with the nanotubes adhered to the surface of the colloids. Near-infrared fluorescence microscopy demonstrates the interfacial band-gap fluorescence of these SWNT-coated particles, suggesting potential routes to novel platforms and applications.
Small-angle neutron scattering has been combined with equilibrium dynamic light scattering to study shearinduced mixing in a diluted high-molecular-weight polymer blend. The data show an enhancement of critical fluctuations upon dilution and are found to collapse onto a universal scaling curve containing no free parameters. This scaling curve is motivated by the theoretical predictions of Onuki and Kawasaki for undiluted binary mixtures. The data also appear to suggest that ''Fisher renormalization'' is relevant in this diluted pseudobinary polymer mixture, consistent with a previous dynamic-light-scattering study. ͓S1063-651X͑96͒52005-2͔ PACS number͑s͒: 61.25.Hq, 64.60.Fr, 64.60.Ht
Optical measurements of the structure and morphology of phase-separating polymer blend under simple shear flow have been performed and the results are compared with computer simulations of sheared phase-separating binary mixtures with viscous asymmetry in the fluid components. Information about the structure is obtained from the two-point composition correlation function. Both experiment and simulation suggest subtle differences in the shear response depending on whether the more viscous phase is dispersed or continuous. Measurements of the string width along the neutral direction suggest power-law decay in the shear rate with an exponent of 1/3 when the more viscous phase is dispersed. The simulations suggest that the mean string width, measured along the velocity-gradient direction in the two-dimensional model calculation, exhibits power-law decay in the shear rate with an exponent of 1/3 independent of which phase is dispersed.
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