There is a boatload of articles on Graphene and tube synthesis. However, I don't see a convincing mechanism on why only MWCNT is formed using the arc-plasma technique and not Graphene (single or multi-layer) or SWCNT (when no catalyst is used).
In other words:
Basically, Graphite is evaporated, and then the graphene sheets formed tend to settle in their lowest energy form, so they roll up to form MWCNT. But the explanation of these low energy is also the same for fullerene (or any form of fullerene), isn't it? I recently read an article where researchers used plasma to exfoliate into 1-3 layer graphene. But I was wondering why did this not form MWCNT if MWCNT is more thermodynamically stable?
Your comments, resources and logic are much appreciated!
Deepak Sridhar
The discussion relates to the topic of thermodynamics and kinetics of chemical reactions. Each reaction is characterized by initial substances, products, thermodynamic parameters (temperature, pressure ...), reaction rate, activation energy and other parameters. It depends on them which path the reaction will take and the thermodynamic stability of the product. The product may also be unstable. Under room conditions, diamond is in a thermodynamically unstable state. It is stable under high pressure and temperature. In the process of synthesizing graphene, tubes may have different options along the way. Specifically, we can talk about a certain size of a graphene sheet with distortion, without distortion, or tubes with or without a catalyst. For anyone interested in these questions, I recommend the book
https://authors.library.caltech.edu/25070/1/FundChemReaxEng.pdf
In the arc discharge technique you will make all kinds of carbon structures, including amorphous carbon, carbon onions and carbon nanotubes. It is far from only MWCNTs that are being produced. Usually the set-up is tuned in order to favour the formation of MWCNTs, but it is far from the only product that one will find in the collected soot.
How Arc plasma discharge technique used for generating MWCNTs, SWCNTs or other carbon nanomaterials, very much depends on the geometrical electrodes, catalysts and experimental controls.
I fully agree with Krister Sevensson. The following topic of arc discharge would answer your question in details.
https://www.sciencedirect.com/topics/engineering/arc-discharge
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