By Cameron Chai
Researchers at the Lawrence Berkeley National Laboratory (Berkeley Lab) of the U.S. Department of Energy (DOE) have developed a fast and easy method to induce nanorods to self-assemble into 1-, 2- and 3-D macroscopic structures. This method may allow nanorods to be effectively used in sensors, solar cells and magnetic storage devices. The mechanical and electrical properties of nanorod-polymer composites can also be increased through this novel technique.
"This transmission electron micrograph (a) shows cadmium sulfide nanorods forming arrays that are aligned and oriented parallel to the cylindrical microdomains of block copolymers. The schematic drawing (b) illustrates copolymers with nanorods."
Block copolymers were used by the research team to direct the self-assembly of nanorods into hierarchical patterns and intricate structures. These copolymers are capable of self-assembling into distinct arrays of nano-sized structures with macroscopic separation distances.
Ting Xu, the project lead and a polymer scientist, informed that the new technique allows them to control the direction of nanorods inside the block copolymers. Self-assembly in nanorods as well as in nanorod-based nanocomposites can be obtained by changing the chemical nature of the nanorods and the structure of the block copolymers. This technique is vital for effective use of nanorods in the development of electronic and optical devices.
Nanorods have electronic, optical and other properties, which do not exist in macroscopic materials. However, to leverage their technological potential, nanorods should be capable of assembling themselves into hierarchical patterns and intricate structures that are similar to proteins.
Back in 2009, Xu and the research team were working with round nanoparticles, generally referred as quantum dots, and had taken block copolymers as partners in this self-assembly attempt. During that study, the researchers joined both block copolymers and quantum dots through tiny adhesive molecules. In the new technique, they again used the adhesive molecules to mediate between the supramolecules of block copolymers and nanorods.
The latest technique can create sequenced arrays of nanorods that are macroscopically joined with adjustable spaces between individual nanorods. This morphology produces plasmonics, a type of materials that offer potential applications in ultra-powerful optical microscopes and superfast computers.
The research has been published in the journal, Nano Letter.