Recent Research Developments

Index of Recent Research News
May 14, 2003
    Soft polymer shells for hard nanostructures

    Recent research on the synthesis of inorganic nanostructuresÖincluding nanospheres, nanorods, nanotubes, and many other nano-objectsÖoffers scientists a diverse ‹nano-toolboxŠ with which to build complex, composite nanomaterials. However, in order to make these objects compatible with the chemistry and processing of composite materials, their nano-surfaces will have to be tailored to their environment. For many of the complex and exotic nanomaterials currently being synthesized, traditional surface chemistry is poorly suited to this task. Recent work by graduate student Youngjong Kang and professor T. Andrew Taton (reported this month in J. Am. Chem. Soc. ASAP, ja034082d) suggests that an alternative approach to modifying the surfaces of nanostructures is to wrap nano-objects in amphiphilic copolymer shells, and then to crosslink the polymer coats to make them permanent.

    Scheme for forming amphiphilic nanocoats around single-walled carbon nanotubes. Amphiphilic block copolymer surfactants are first assembled around hydrophobic SWNTs, and then the hydrophilic blocks are chemically crosslinked via EDC-amide chemistry to form a permanent shell. Inset: TEM image of an encapsulated SWNT.

    Kang and Taton have demonstrated this approach first on single-walled carbon nanotubes (SWNTs). SWNTs are notoriously difficult to disperse in solvents and polymer matrices, and the strong van der Waals attraction SWNTs have for one another usually drives them to form tangled mats and ropes. Although this might be solved by chemically modifying the polyaromatic surface of the nanotubes, this can drastically change the electrical and mechanical properties of SWNTs. However, Kang and Taton found that SWNTs can be encapsulated inside micelles made from polystyrene-poly(acrylic acid) copolymer, and that these micellar shells can be crosslinked to form uniform ‹nanocoatsŠ. Once these nanocoats have been formed, they are not removed by hydrophilic or hydrophobic solvents, by compositing the coated nanotubes with polymer matrices, or by high-temperature materials processing. As a result, this report may not only improve the formation of SWNT composites, but also help stabilize dispersions of the many nano-objects that materials chemists can now synthesize.

    Encapsulated SWNTs suspended in: (A) water; (B) THF; (C) chloroform; (D) 1% agarose gel; (E) 1% agarose gel, after drying; (F) styrene-butadiene elastomer.

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Next scheduled update: May 28, 2003.

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