Interactions between Block Copolymers and Single-Walled Carbon Nanotubes in Aqueous Solutions: A Small-Angle Neutron Scattering Study

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• 作者：Meirav Granite ; Aurel Radulescu ; Wim Pyckhout-Hintzen ; Yachin Cohen
• 刊名：Langmuir
• 出版年：2011
• 出版时间：January 18, 2011
• 年：2011
• 卷：27
• 期：2
• 页码：751-759
• 全文大小：1167K
• 年卷期：v.27,no.2(January 18, 2011)
• ISSN：1520-5827

文摘

The amphiphilic copolymers of the Pluronic family are known to be excellent dispersants for single-walled carbon nanotubes (SWCNT) in water, especially F108 and F127, which have rather long end-blocks of poly(ethylene oxide) (PEO). In this study, the structure of the CNT/polymer hybrid formed in water is evaluated by measurements of small-angle neutron scattering (SANS) with contrast variation, as supported by cryo-transmission electron microscopy (cryo-TEM) imaging. The homogeneous, stable, inklike dispersions exhibited very small isolated bundles of carbon nanotubes in cryo-TEM images. SANS experiments were conducted at different D₂O/H₂O content of the dispersing solvent. The data for both systems showed surprisingly minimal intensity values at 70% D₂O solvent composition, which is much higher than the expected value of 17% D₂O that is based on the scattering length density (SLD) of PEO. At this near match point, the data exhibited a q^鈭? power law relation of intensity to the scattering vector (q), indicating rodlike entities. Two models are evaluated, as extensions to Pederson鈥檚 block copolymer micelles models. One is loosely adsorbed polymer chains on a rodlike CNT bundle. In the other, the hydrophobic block is considered to form a continuous hydrated shell on the CNT surface, whereas the hydrophilic blocks emanate into the solvent. Both models were found to fit the experimental data reasonably well. The model fit required special considerations of the tight association of water molecules around PEO chains and slight isotopic selectivity.