Why is nanotechnology the “new kid on the block” and in ten years become a major direction of cutting-edge research, one example could be a quantium leap in energy storage. What is wrong with the batteries that we use now, that nanotechnology could soon make them obsolete, you might ask?
In some ways the “dimension” of “nano”, is a very different one than the world of that of the macro, the one that we conscious about, all though both exist at the same time. For example, using biology as an example, the without the nano component, we would not be here today. The forces that predominate in the nano world make possible DNA, and the proteins and enzymes that are made from DNA make our very existence possible. Of course the flip side these predominating forces makes one of the ultimate nano “machine” possible, viruses but not all viruses are “bad.”
“Bacteriophages (phages) are viruses that infect bacteria. Typical phages have hollow heads (where the phage DNA or RNA is stored) and tunnel tails, the tips of which have the ability to bind to specific molecules on the surface of their target bacteria. The viral DNA is then injected through the tail into the host cell, where it directs the production of progeny phages often over a hundred in half an hour. These "young" phages burst from the host cell (killing it) and infect more bacteria…Therapeutic phages can potentially be developed against any bacterial infection. Obviously, because of their "mode of action", phages can not be used to treat viral infections (e.g., influenza or herpes).”[i]
These forces also make materials that in the nano state behave quite differently in the nano dimension. Combine the increased effect of thermal vibration and the so-called “weak” forces in the macro dimension, self assembly becomes possible as the necessary parts are vibrated until the achieve the correct position, or the jostling of the parts breaks up the wrong positions and forces the parts to try again and again until the get it “right.”
However, moving form biology/medical applications, in my RET-NANO course I’m working with Patricia Valenzuela on research improving the characteristics of lithium ion batteries so that a “super” lithium battery is produced. The “super” would imply faster charge (and discharge rates) and vastly improved cycling from the current 5,000 to 100,000 times; using nano technology changing not the efficient lithium canode, but the anode (graphite). Currently the cathode, graphite, is not a nano material that degrades rather quickly by the stress imposed by in the charging & discharging process. Other issues a result of intercalation of the graphite with lithium ions during the charging process, is the slow charge (and discharge) rate imposed by the relatively long distances involved with moving ions into the 2 dimensional planes of the graphite anode.
The study of lithium diffusion in carbon materials is of great interest in both theoretical and practical aspects. During recent two decades this process was studied mainly in connection with the development of lithium ion batteries. Such batteries have negative electrodes based on graphite and other carbon materials.[iii]
In Dr. Yury Gogotsi’s nanotecnology lab I am working with carbon nanotubes, filled with nano sized (~5NM) silicon particles using capillary action. Sonification is used to disperse the silicon particles into a solution. However, much like trying to put a camel through the eye of a needle, the origonal silicon particles must be reduced in size.
This requires hydrofluoric acid (HF) and nitric acid (HNO3) sometimes diluted with deionized water (to slow the reaction enough so that there is time to stop it as the 5 nm size is attained). The first samples of silicon particles we “nano-sized” with our solutions was 0.003 grams of Silicon, later we tried 0.006. HF will clear of a layer of SiO2. HNO3 then oxidizes the next layer of Si and HF the clears that layer of SIO2. One could compare this process to that of pealing and onion, layer bye layer. Again sonification is used to keep the silicon suspended in solution, while this size reduction proceeds.
When the correctly sized silicon particles are produced, photoluminescence is clearly seen under 254 nm ultra violet, the range in color can be from red to green. To slow desired reaction one the particle size is correct methanol is added. The particles are filtered out of solution using a ceramic filter holding a polyvinylidene fluoride (PVDF) membrane filter, and washing of the silicon continued until the pH was neutral.
Since silicon is very reactive in air (with oxygen, forming SIO2), it needed to be stabilized. For this we used 1-octadecene and ultra-violet cabinets, leading to the photoinitiated hydrosilylation of the silicon; some of the 1-octadecene reacted with the 4 hydrogen atoms on the silicon (like carbon, silicon has a valence of four). Part of the octadecene molecule removed the hydrogen atoms, the rest of the organic C-H chain, then bonded with the silicon. The excess 1-octadecene molecules were removed in a vacuum oven at 90 degrees celcius.
This product was then dispersed in toluene (which was not degassed and remained saturated with dissolved oxygen), and was capped to prevent evaporation, and also subjected to UV radiation. This time we wanted dissolved oxygen in the mixture, as the oxygen would then insert itself into between the silicon and the organic chain forming a secure double bond.
[i] http://www.phages.org/PhageInfo.html (accessed 7/26/2008) General Information about Bacteriophages
[ii] How Stuff Works (accessed 7/21/2008) http://electronics.howstuffworks.com/lithium-ion-battery.htm