Richard Feynman is lauded as the grandfather of the nanotechnology revolution. In 1959, he gave a talk to the American Physical Society entitled "There's Plenty of Room at the Bottom", paving the way for a generation of technologies exploiting our understanding of very small scales.
The Reach of Nanotechnology
Nanotechnology is no longer the stuff of science fiction, or even abstruse research. Scientists are manufacturing better catalytic converters, delivering tiny doses of drugs to cells and even making stain-repellant clothing, all thanks to the ability to order the very small to their liking. The titanium oxide in high-end sunscreen and new "easy-clean" ceramics are evidence of nanotechnology in action. The world of scientific interest is, quite literally, getting smaller.
Cost-Effective Manufacturing of Nanotubes, Nanowires and Nanodots
Cheaper ways to make the nanotubes used in high-density storage devices, and the nanowires and nanodots used in thin film solar cells and nanosolar devices, are of particular importance to researchers and manufacturers alike.
There is, however, a major bottleneck on the march towards successful large-scale production of nanomaterials, and that is cost. Manipulation at the molecular level is expensive and fraught with error, and as such scientists are turning to innovative methods to get their nano-soldiers in line without the costly business of manually forcing them into order.
What is needed is a class of nanomaterials that naturally 'grow' into the structures needed for industrial applications, without costly human interference. These materials exist through the magic of self-assembly, a set of technologies that have the potential to complete the nano-revolution. Physicists, chemists and biologists are working together to build things the way nature does it - by exploiting the underlying interactions between molecules.
Self-assembly and Diblock Copolymers
One such molecule, brought to us by advances in polymer science, is the diblock copolymer, the doyenne of self-assembly. Diblock copolymers are long, thin, molecular strands containing two linked chains of single molecules called monomers in a structure such as:
A-A-A-B-B-B
Ensure that 'A' monomers repel 'B' monomers and place large numbers of these molecules in a high-temperature 'melt', and interesting things happen. Entropy causes polymers to coil up, but repulsive interactions between the 'A' and 'B' monomers would favour stretched polymers. The interplay of these competing interactions as the temperature, and thus the entropy, of the system increases, causes remarkably complex structures to emerge.
In its lowest temperature state, a diblock copolymer melt will form alternating sheets of 'A' and 'B' monomers. The 'A' and 'B' sides of the polymer are bonded and can never escape each other completely, so they take the next best option and form into layers - a phenomenon known as microphase separation.
As the temperature, and thus the entropy, of the system increases, other microphases begin to emerge. First, we see the sheets break up into long, regular, thin cylinders. Then they break again into tiny, perfect spheres. Finally, at very high entropy, the coiling takes over and the melt becomes completely disordered.
Confine a diblock copolymer melt to a cylinder and even more interesting things happen. Corkscrews, donut shapes and double helices are all within the reach of the phase separation of this versatile molecular artisan.
Consequences for Solar Cell Manufacturing and Storage Devices
These discoveries, made experimentally in the last twenty-five years and only understood theoretically in the last fifteen, have wonderful consequences for the scale and cost of nanomaterial production. If we understand diblock copolymer melts well enough, we will be able literally to 'grow' lithographic templates, on tiny scales, to make sheets of nanotubes, nanowires and nanodots crucial for applications in everything from thin film solar cells and high-density storage media, to quantum computers. IBM announced in 2003 that they had used self-assembly to make prototype transistors.
More deeply, this new way of thinking about manufacturing marks a leap forward in our ability to control our environment. From the assembly line to the self-assembly line, scientists are increasingly looking to exploit, rather than to control, natural processes. This idea has a depth of reach that only decades of further research can bring to fruition.
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