Jim Dempsey weighs in on the Pugno paper…

The estimable Jim Dempsey (again, via Andy Price) weighs in on the Pugno controversy and Dr. Brad Edwards comments on it.  Writes Mr. Dempsey;

Brad, your response was a good “well wait a minute” response. In particular, from my unfounded point of view, I key in on your statement:

– assumes that all CNTs will be damaged (it appears to be on a 100 nm length) and that
– none of them interact with each other in a supportive manner.

One of the major factors in building suitable SE tether material is in obtaining adequate supportive interaction without the expense of unwieldy excess mass. Anyone familiar with traditional cordage understands that supportive interaction is the key element in constructing a reliable defect tolerant cord (tether in this case).

As a thought experiment assume one were to produce 100,000KM long SWNT.  Assume you were to somehow clamp only the ends of the bundles. Given this scenario (and excluding Van der Vaal’s or electrostatic interaction) any defect subsequently introduced into a given SWNT in the bundle would weaken the bundle by one SWNT capacity. It is a virtual certainty that given the length of each SWNT this unsupportive bundle would quickly degrade. By the introduction of a suitable supportive interaction mechanism, the load bearing capacity of a damaged SWNT can bypass the local of the defect. In reading Pugno’s paper there appears to be no anticipation that a suitable supportive interaction mechanism could be found any time soon.

I am optimistic. I believe the problem is solvable, I believe it will be solved; I believe it will be solved within 5 years. But what would I know; I am not a molecular chemist.

If I “were” a molecular chemist, I would be a brash molecular chemist, I would buck the establishment, I would not be afraid to say “why not”.

I would take what little I do know, and inject this knowledge into an unrestricted pool of properties and characteristics, then draw upon this to produce subsequent precursor knowledge which goes back in the knowledge pool, and repeat the process until the solution is found.

Our current problem of finding the ideal (an acceptable) supportive interaction mechanism could potentially be an ideal candidate for genetic programming (see: http://www.genetic-programming.com/johnkoza.html).

What we know is:

Using an Atomic Force Microscope you can place and move about individual atoms on a flat crystalline surface.

We know that a supposedly flat crystalline surface at the atomic scale is bumpy.

We know that given different specimen atoms for a given surface will have different affinities to “stick” within depressions of the bumpy surface.

Given this knowledge:

I would begin experimentation with a graphene planar surface.  The experimentation preferably could be performed by way of genetic programming as it would be much faster and more comprehensive than physical lab work.

The elusive prey would be that which causes good “stiction”.  Something that “falls” deep into the surface but does not penetrate the surface. The test subjects need not be limited to atomic (ionic or charge neutral) selections but would also include molecular forms.

Next, with this reasonably large collection of potential candidates, reconfigure the simulation (or lab tests).

Then experiment with “dusting” the SWNT and bundling the SWNT to determine an optimal candidate and dusting density which produces good protection against slippage between SWNT and who’s dusting density is commensurate for the anticipated probability of environmental damage to the SWNT.

Added to the mix I would experiment with collecting various numbers of said dusted SWNT bundled and held together with a cladding.  The purpose of this cladding is not to add tensile strength but to ensure a tight binding of the SWNT bundles such that the stiction from the dusting can do its work.

The said above dusted, bundled and cladded SWNT’s would be produced in large quantities and would exhibit the mechanical and processing properties of micro fibers. Call these DBCSWNT (Dusted, Bundled, Cladded SWNT).

The above DBCSWNT would be placed en mass into a binding mixture of PET or PET-like agent and drawn many times to ensure good alignment and packing density of the DBCSWNT. Then after evaporation of solvent and curing of binder the end result is a thread of any desired length and diameter. The cross section of which need not be circular. Hexagonal cross section might be a better choice.

These threads would then be twisted or braided into larger diameter cordage (fractional mm) which is finally incorporated into the ribbon.

To date, and without being privy to what is being done, experimentation is being performed by placing the SWNT directly into the PET or PET-like agent, i.e. the stiction dusting and cladding steps above are omitted. It is my gut feel that the key to or breakthrough to manufacturing suitable tether material is in the stiction dusting and cladding components of the above mentioned process. But then, what to I know, I am not a molecular chemist.
 
Jim Dempsey

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