Piezochemical mechanosynthesis

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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".

Piezochemical mechanosynthesis (shorthands: piezomechanosynthesis or just piezosynthesis) is the high force, torque, and bending moment applying pick-and-place-assembly of single atoms and minimal molecule fragments (aka moieties) into larger structures. Target structures are typically highly polycyclic molecules out of stiff gemstone like compounds. What here is called crystolecules. Crystolecules do not occur in nature and cannot yet be produced via today's (2021 …) thermodynamic means of producton.

Conditions for piezichemical mechanosynthesis:

  • (1) trajectories of atoms and molecule fragments is fully positionally constrained (down to acceptable thermal vibration amplitudes)
  • (2) it applies (high) forces, torques, and bending moments

Full positional constraint (1) is a prerequisite for applicability of forces, torques, and bending moments (2).

Context

Piezosynthesis is an especially promising far term target of the bigger class of all types of mechanosynthesis.
The bigger class of mechamosynthesis just requires some (preferably higher) degree of positional constraint (1).
Mechanosynthesis in the wider sense does not require high forces. Assembly processes with only weak external forces or pretty much no external forces involved are also included.
If the requirement on positional constraint is weakened too much, then it's just semi mechanosynthetic assembly.
That is essentially what natural anabolic enzymes do. ("Anabolic" means building up. Enzymes are proteins that form or break bonds catalytically.)
If the requirement on positional constraint is pretty much removed all together than the assembly process is some form of the many forms of self assembly.

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 piezochemical mechanosynthesis.

Where force applying mechanosynthesis will be performed

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

Factors influencing expectable throughput

Factors that 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 that 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.

How this influences gem-gum factory design

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 design constraint leads to the optimal solution (natural choice) being such that it includes
many groups of factory lines. Each group piezosynthesizing one specialized standard part with no (or only small) variations.

The lines can be spatially compact in cross section due to each line being mostly hard-coded (think: spacer wedges)
There's no need for (necessarily much bigger) general purpose robotics that can make each part completely differently.
At least for the the lowest assembly level where the piezochemical mechanosynthesis happens.
Higher up in the hierarchy of convergent assembly increasingly more general purpouse assembly robotics can be integrated.

Related: Mechanosynthesis core
A possible "exception confirming to the rule": Piezosynthesis tuning core.

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.

See: Experimental demonstrations of single atom manipulation

Sate of theoretical modelling

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

Such more advanced simulations have been performed extensivly on mechanosynthesis of diamond and related pure carbon compounds (allotropes).
See: Tooltip chemistry and "A Minimal Toolset for Positional Diamond Mechanosynthesis (paper)"

Surprising facts

This is about 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 (parallel, unpaired, triplet sate) then 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, paired, singlet state) can be influenced by nearby massive atoms with high spin orbit coupling.
See Nanosystems 8.4.4.b Radical coupling and inter system crossing (Wikipedia: Intersystem crossing)
Related: Inter system crossing, Fun with spins

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 piezochemical 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 atoms.
These are used in molecular dynamics simulations.

Related

Analysis, theory, and ideas

  • Nanosystems Chapter 8 Mechanosynthesis => 8.5. Forcible mechanochemical processes

The basic duo

The surprising tricks

Types of chemistry

Places for unnatural tooltip piezochemistry

Superclasifications

External links

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