In this video ( "Mechanosynthesis - Ralph Merkle & Robert Freitas" )
R.Freitas says that you don’t take mechanosynthesized stuff apart again.
See here: (Jump forward to 47:42)
Guy in audience: "If I place a germanium incorrectly which tool do I use to get it off."
R.Freitas "You don't."
So the Set described in the there discussed tooltip paper
( http://www.molecularassembler.com/Papers/MinToolset.pdf )
is not reversible in the bond-topology-state.
The set was also not simulated in a way that maximizes reversibility in energy but instead in a way that
makes it somewhat reliable at 300K (E_react = 0.40 eV gives P_react = 2*10^-7)
and extremely reliable at 80K (E_react = 0.40 eV gives P_react = 5*10^-26 at)
But most importantly the reactions where considered standalone and uncoupled to others.
According to E.Drexler mechanosynthesis can be made to archive very high levels of energy reversibility:
... reliable mechanochemical operations can in some instances approach thermodynamical reversibility in the limit of slow
motion. ... ... The conditions for combining reliability and near reversibility are, however, quite stringent: reagent moieties must on encounter have structures favouring the initial structure, then be transformed smoothly into structures that, during separation, favour the product state by ~ 145 maJ (to meet the reliability standards assumed in the present chapter). ...
* "smoothly" I think means forces times movements must be captured in the machine phase background. Holding against pulling force - preventing ringing snapping.
* Furthermore I think that one needs to couple multiple reactions with E_react-one<<kB*T energy-loss per deposition/abstraction
together to E_react-all>kB*T as a whole to prevent the single reactions from running backwards.
I made a 3D model for visualizing the qualitative progression of the energy wells that is necessary for a energetically reversible mechanosynthetic operation. This model is quantitatively disconnect from any particular physical process like e.g. hydrogen abstraction.
The question is:
Can one imply from energetical reversibility to bond-topological reversibility?
Surely it seems difficult to rip out a carbon from the centre of a flat diamond say 111 surface.
But if the atomically flat plane does not have macroscopic size one can start from the edges where less than three of four bonds are inaccessible. Astoundingly there was an AFM experiment conducted where on an atomically flat surface buried tin atoms where controllably flipped with silicon atoms and vice versa (surface-to-tip).
They used a lot of tapping and akin to what E.Drexler describes as "conditional repetition"
I think to find an answer to this question is highly relevant for recycling (in the advanced end of the technology spectrum)
The official nano-factory video says something like "the only waste products are clean water clean air and heat".
But what about the product itself once its microcomponents become obsolete?
If mechanosynthesis can't be made bond-topologically reversible from the early on start the only way to get rid of obsolete versions would be by:
* burning them - only possible if they don’t form slack due to incorporated Si,Al,Ti,...
* dissolving them (Sodium beam treatment, Acids, ...)
If even that will not be done we might sink deeply into diamondoid waste.
I think that might be the most severe and most overlooked danger of APM.