To understand the function of nanoscale materials we need to dip our toes into a discussion of quantum physics. One of the key precepts of quantum physics is that particles and energy waves called photons (like light) can only have distinct amounts of energy, as opposed to having any value of energy along a continuum. The differences between the energy states are called quanta. Quantum physics also tells us that fundamental particles, such as electrons or quarks, have a spin state, described as up or down. Spinning particles exist in pairs, one with up spin and one with down. It’s as though the nanoscale world is digital rather than analog. The most spectacular, everyday manifestation of quantum physics is the rainbow. The hot hydrogen and helium atoms in the sun give off photons of light of precise and specific energy values characteristic of their atomic structure. When refracted by raindrops we see these photons of light arrayed in the colors of the rainbow.
Other aspects of quantum physics are much harder to both understand and explain. Perhaps the most exotic is quantum entanglement, which stumped even Albert Einstein. Quantum entanglement works as follows: let electrons A and B be a spin pair with A spinning up and B spinning down. If energy is applied to A to flip its spin to down, B will immediately flip its spin to up. The amazing part of this process is that B’s spin will flip sooner than the time it would take for light to travel from A to B. This was at odds with Einstein’s view that no information or energy in the universe could travel faster than the speed of light. The mechanism responsible for quantum entanglement remains a mystery to this day.
The appeal of nanotechnology stems from the fact that the physical and chemical properties of materials less than 100 nanometers exhibit behavior based on quantum physics that are not apparent in larger objects. For example, at the nanometer scale copper turns from opaque to transparent, aluminum becomes flammable (even explosive), and carbon atoms can be assembled into nanotubes which are 100 times stronger than steel while having only one sixth of its weight. These changes in properties, of which we are only in our infancy of discovering, are what drive the interest in nanoscale devices.
While quantum physics calculations had long suggested that potentially useful, even revolutionary, devices could be made at the nanoscale level, construction of them was not really possible until the invention of the Scanning Tunneling Microscope (STM) in 1981. The STM works on another fascinating principle in quantum physics called quantum tunneling which, for the sake of brevity and to spare myself the challenge, I will leave unexplained. The beauty of the invention of the STM was the ability to image materials at the nanoscale level so you can see the individual atoms. Without this ability you could not “see” the nanomaterials you were attempting to construct.
With the STM in hand, research and entrepreneurship in nanotechnology took off. Current applications of nanomaterials include titanium dioxide particles in your sunscreen which are dramatically better at blocking UV rays compared to larger titanium dioxide particles, and the silver, bacteria-killing nanotubes which have been added to Band-Aids® to promote healing and socks to cut down on foot odor. You might think that silver is a rather expensive material to use for something as mundane as foot odor control. However, since the effectiveness of the silver nanotubes is directly dependent on their extraordinarily small size, a minute amount goes a long way. We’ll touch on silver nanotubes again later.
The potential for new inventions based on nanotechnology is hard to exaggerate. I like to think of it this way. Since the origin of our species millions of years ago, we have been utilizing the macro-scale (>100 nm) materials available to us on Earth to spectacular effect. Think rockets, iPads®, artificial joints and Cheez Whiz®. But with the advent of nanomaterials and their surprising and unique properties, it’s almost as though we have an entire new planet of materials to work with.
There are far too many potential applications of nanotechnology to include a comprehensive review, so here are several that I find intriguing.
- Nanoscale devices may result in dramatically improved solar cells. An improvement of solar cell efficiency from the current level of 20% to 40-50% would transform global electricity production.
- Quantum computers based on instantaneous quantum entanglement could result in machines that make today’s supercomputers look like the Model T.
- Nano-robots could be launched in the upper atmosphere to rebuild the ozone layer.
- Nanotechnology could provide dramatic improvements in fighting cancer. One approach I find promising is the construction of gold, chemoactive agent containing that have receptors which can bind to cancer cells. With this approach, chemotherapy could be delivered directly to tumors while sparing patients the ravages of having these toxic drugs coursing through their entire bodies.
Unfortunately, the same properties that make nanomaterials attractive, their small size and physical and chemical reactivity, make them potentially dangerous. Remember the socks with the silver, antibacterial nanotubes? When you run them through the laundry, some of the tubes wash off and enter local water-ways where they kill beneficial bacteria. The production and use of nanomaterials also presents significant respiratory risks. We already know that inhaling particulates from coal mining, smoking, or asbestos can cause lung cancer. Breathing in tiny, chemically-active nanoparticles would likely be far worse, a concern which is supported by laboratory studies with mice.
In the final analysis, nanotechnology shares the same characteristics as most new scientific developments, the potential to result in both great benefit and significant harm. Our challenge as a society will be to utilize them responsibly. Undoubtedly, we will make some mistakes along the way, but in the end the results are likely to amaze.
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