Revision as of 12:17, 12 April 2021

A single hydrogen atom is deposited onto a cylindrical crystolecule under construction. The tooltip used here is the HDon tool that has been theoretically analyzed in the paper: "A Minimal Toolset for Positional Diamond Mechanosynthesis". See tooltip chemistry

By smartly crafting the temporal trajectory of the potential wells for tool-tip and work-piece-surface mechanosynthesis can be made vastly more efficient than "normal chemistry".

This kind of mechanosynthesis:

• is fully positionally constrained
• applies forces and torques

Full positional constraint is a prerequisite for applies forces and torques.

Unnaturality of the process

Force applying mechanosynthesis is a rather unnatural process. Unnatural chemistry so to say.
Some natural enzymes may be able to provide sufficient positional constraint such
that some small forces and torques are involved in bond reconfigurations.
But anything there is minute compared to the magnitude of forces and torques that
will be involved in force applying mechanosynthesis will use.

Where force applying mechanosynthesis will be performed

This would be performed in the molecular mills of future gem-gum factories. For:

• picking molecules up into machine phase
• Tooltip preparation in a tooltip preparation cycle. Making molecules into reactive moieties.
• Final deposition of moieties onto the crystolecules under assembly (under synthesis).

Factors influencing expectable throughput

Factors increase throughput:

• The forces and torques allow to massively speed up chemical reactions.
• The forces and torques make almost all attempts for reaction succeed unlike normal chemistry where its often more the reverse.

Factors decrease throughput:

• Unavoidably fat fingers reduce the number of reaction sides per volume compared to natural chemistry.
• Slow down of machinery speeds at the smallest scales to reduce dynamic friction in the many superlubricating nanoscale bearings.

While decreased spacial reaction site density cancels out with the increased temporal reaction frequency quite a bit
it is still important to keep the individual assembly cells (as in: volume per active reaction site) as small as possible.
This leads to a hard coded standard part factory line manufacturing design as the natural chice for the lowest assembly level.

Research and development (R&D)

Sate of experimental results

There have been successful experiments with silicon, and hydrogen on silicon.
Albeit this was done with non atomically precise tips. And thus still very crude.

Sate of theoretical modelling

Extended simulations have been performed on mechanosynthesis of diamond and other pure carbon compounds (allotropes).
See: Tooltip chemistry

More advanced quantum mechanically accurate simulations are needed compared to
the simulation of molecular machine elements where
often much simpler and more scalable molecular dynamics simulations suffice.

Aspects of (force applying) mechanosynthesis that may come unexpected

When mechanosynthesis is designed to minimize energy dissipation high reliability and near reversibility can be archived at the same time. To do this the reactant moiety must on encounter favor the initial structure and must then be smoothly transformed into a configuration that sufficiently favors the product structure. Multiple retries (conditional repetition) can further lower power dissipation by a good chunk.
See Nanosystems 13.3.6. Error rates and fail-stop systems b. Energy dissipation caused by chemical transformations.

If e.g. ethyne is used as resource material (that is the carbon is not drawn from atmospheric CO₂) and the excess hydrogen is recombined to water diamondoid mechanosynthesis is exoergic. [Todo: check balance when storing compressed hydrogen?]
See Nanosystems 14.4.8 Energy output and dissipation The excess energy of mechanosynthesis can be used to drive mechanosynthesis.

A pre-organized polarized local atomic environment can create a very high local electric field at the mechanosynthesis site lowering the transition state energy and increasing reaction rate. This effect can surpass the one a polar solvent can have.
See Nanosystems 8.3.3. Basic capabilities provided by mechanosynthesis b. Eutactic "solvation."

When spins are misaligned (repulsive parallel singlet state) pressing the reactants together to fast can slow down the reaction instead of speeding it up. Spin flips in tool-tips (to create an anti-parallel bonding singlet state) can be influenced by nearby massive atoms with high spin orbit coupling.
See Nanosystems 8.4.3.b Radical coupling and inter system crossing (Wikipedia: Intersystem crossing)

Short sloppy (that is non-diamondoid) hydrocarbon chains can be made by tensioning the already produced part and doing manipulations near one of the two tips with a third one. See: Mechanosynthesis of chain molecules.

Suggestive memorization help for the concept of mechanosynthesis

• Stiffness combined with …
  
• … forceful and skillfull repeated reziprocative interaction on …
  
• … tightly bond partners is the key to …
  
• … reliable success when trying to reach the desired reaction.
  

(More of this: "Accidentally suggestive")

Why forces (and torques) between atoms are rarely mentioned in chemistry and physics

Precisely because this is very difficult to do experimentally. Usually one talks about energies which are much more easily measurable via various forms of spectroscopy.

Even with our current day macroscopic scanning probe microscopy which
provides a direct means for probing such forces this is quite difficult.

• Bond forces can be derived from the changes of energy with bond distance (first spacial derivative)
• Bond Stiffnesses can be derived from the changes of force with bond distance (second spacial derivative)

From the equilibrium bond energy alone (as found in bond dissociation energy tables) bond forces can not be derived.

There are quite good classical (non quantum mechanical) approximation models for forces and torques between. These are used in molecular dynamics simulations.

Related

• The various forms of Mechanosynthesis
• Mechanosynthesis
• Raw materials
• Mechanosynthesis core

External links

• Wikipedia: Bond-dissociation_energy