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Self-Assembling Nanorods: Berkeley Lab Researchers Obtain 1, 2 and 3D Nanorod Arrays and Networks

2012-02-01 20:10
A relatively fast, easy and inexpensive technique for inducing nanorods - rod-shaped semiconductor nanocrystals - to self-assemble into one-, two- and even three-dimensional macroscopic structures has been developed by a team of researchers with the U.S. Department of Energy (DOE)в s Lawrence Berkeley National Laboratory (Berkeley Lab). This technique should enable more effective use of nanorods in solar cells, magnetic storage devices and sensors. It should also help boost the electrical and mechanical properties of nanorod-polymer composites. Leading this project was Ting Xu, a polymer scientist who holds joint appointments with Berkeley Labв s Materials Sciences Division and the University of California (UC) Berkeleyв s Departments of Materials Sciences and Engineering, and Chemistry. Xu and her research group used block copolymers - long sequences or blocks of one type of monomer bound to blocks of another type of monomer - as a platform to guide the self-assembly of nanorods into complex structures and hierarchical patterns. Block copolymers have an innate ability to self-assemble into well-defined arrays of nano-sized structures over macroscopic distances. Future work will look at assembling nanorods into tetrapod and other shapes. Transmission electron micrograph (a) shows cadmium sulfide nanorods forming arrays that are aligned and oriented parallel to the cylindrical microdomains of block copolymers. Schematic drawing (b) illustrates copolymers with nanorods. Nanoletters - Direct Nanorod Assembly Using Block Copolymer-Based Supramolecules Ours is a simple and versatile technique for controlling the orientation of nanorods within block copolymers, Xu says. By varying the morphology of the block copolymers and the chemical nature of the nanorods, we can provide the controlled self-assembly in nanorods and nanorod-based nanocomposites that is critical for their use in the fabrication of optical and electronic devices. Nanorods - particles of matter a thousand times smaller than the stuff of todayв s microtechnologies - display highly coveted optical, electronic and other properties not found in macroscopic materials. To fully realize their vast technological promise, however, nanorods must be able to assemble themselves into complex structures and hierarchical patterns, similar to what nature routinely accomplishes with proteins. Xu and her research group first enlisted block copolymers as allies in this self-assembly effort in 2009, working with the spherical nanoparticles commonly known as quantum dots. In that study, they lashed quantum dots to block copolymers via a mediator of small adhesive molecules. In this latest development, Xu and her group again made use of adhesive molecules, but this time to mediate between the nanorods and supramolecules of block copolymers. A supramolecule is a group of molecules that act as a single molecule able to perform a specific set of functions. Block copolymer supramolecules self-assemble and for...
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