Recent Research Developments

Nanotube-Directed Alignment in Anisotropic Materials

Anisotropic materials exhibit different properties depending on the direction they are observed. For example, some anisotropic polymers are rigid in one direction but rubbery in another, or transparent when viewed from one angle and opaque from a different angle. For many anisotropic materials, anisotropy is determined by a localized, preferred molecular or supramolecular ordering. Optimizing the anisotropic properties of such materials requires that the orientation of individual domains be closely controlled over macroscopic distances. Members of the Taton Group are developing methods to achieve coalignment of anisotropic materials by using rigid nanoscale rods to align anisotropic organic materials.  Graduate students Randy Mrozek and Byeong-Su Kim, and undergraduate Vince Holmberg, have reported in the December issue of Nano Letters that single-walled carbon nanotubes will nucleate the growth of oriented, liquid-crystalline polymer (LCP) domains (Nano Letters 2002, 12, 1665-1668). In a pure liquid­crystalline polymer (such as Kevlar® aramid), domains typically grow as spherulites, with polymer molecules oriented radially from the nucleating center. However, when carbon nanotubes were present in a model LCP, domains grew as uniformly colored spheroids, indicating a single molecular orientation. The coupling of preferential nucleation and controlled domain growth may allow for the production of bulk LCP materials by orienting a small amount of SWNT seeds prior to domain formation. This work is expected to aid in the development and application of macroscopically ordered, nanostructured composites which may have enhanced anisotropic properties compared to their relatively disordered parent materials.

Scheme for aligning anisotropic materials with nanorods.



Time-lapse images of liquid crystalline domains growing from an isotropic polymer melt. The sample on the left contains less than 0.001% carbon nanotubes, and these nanotubes serve as seeds to template the growth of uniform, football-shaped domains. On the right, cooling pure liquid crystalline material results in fan-shaped and spherulitic textures.

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