Nanoscale actuators

This is basically about xxx-mechanical converters.
Where xxx is electrical, chemical, optical, thermal, …

Actuators in early atomically precise manufacturing

For early technology levels (level 0 and level 1) of the incremental path there are several options.

Early optical actuation

This is about optomechanical converters based on molecules that change shape in response to
a change of electronic configuration in response to a photon lifting one (or more?) electron(s) to a higher energy molecular orbital.

Optically activated shape changing molecules may easily be overloaded

This exerts very little force.
If a bond is under too much load optical actuation will likely not happen.
The right way to make optomechaniocal actuators from light activated molecules is likely to
organize light activated molecules collectively where each acts only against a
weak non-bonded interaction (way weaker than the covalent bond that gets flipped in orientation).

Forces on bonds will change Fermis golden rule for optically induced electronic state transitions

Fermis golden rule for electronic transitions activated by incoming light.
Mechanical loads on the bonds (bonds being represented by the electronic state of bonding molecular orbitals)
will likely change transition rates in non-trivial ways.
It should be possible (and already quite challenging) to make a first order linear approximation.
Hopefully a first order approximation will be sufficient for the forces and light to expect.
(TODO: Investigate whether it has been investigated how mechanical loads on bonds influence Fermis golden rule.)

The issue of photo-bleaching

Irreversible damage to light activated configuration changing molecules.
An highly undesired physical effect.
Perhaps this effect can be reduced by orders of magnitude via:

• integration into machine phase - keeping it away form other chemical species that migh catalyze dgradation
• choice of the right type of molecule

Example molecules

See external links.
(wiki-TODO: Add example molecules.)

Solvation mixture change based pseudo actuation

The prime example here are likely DNA walkers.
By consecutive mixing in of short DNA strands a walker can be moved along a chain of
DNA strands that are about equidistantly strung along some transport-rail-backbone.
Which may or may not be stiff and straight.

Note that the actuation applies no active force here.
Transport is only due to thermal motion and dissipation of energy for binding at the next site.
This the "pseudo" prefix to actuation.
This is related to non-equilibrium Brownian ratchet actuation.

Changing of salt concentration can induce selfassembly as has been experimentally shown.
Maybe this could be used for actuation too somehow.

In any case these forms of actuations are very slow.
Going to microfluidics where change of composition of solution can be much quicker should allow for massive speedup.
But reaching speeds possible by e.g. electrostatic actuation is probably unlikely.
For more advanced systems (dry gas or vacuum environment) solution chemistry based actuation is
fundamentally inferior to electrostatics based actuation.

Early electrostatic actuation

To note here is maybe:

(1) Conductive electrolyte can shield external electric off fields quite a bit, which is rather undesirable.
Fields are not shielded off fully though as working experiments show. (2) Some early foldamer technologies like structural DNA nanotechnology may
not work in dried out conditions without water or other polar ion carrying solvent.

There where successful experiments of electrostatically actuating a rod of structural DNA nanotechnology
and this was orders of magnitude faster than all the preceding means of actuation by adding or (more difficult) removing chemical species like e.g.:

• adding (short) oligomer DNA strands for site-specific-locking after free thermal motion
• changing salt concentrations for larger scale selfassembly or disassembly

Nanoscale actuation by pressure (advanced and early APM)

Actuation by variations of pressure for foldamer systems has not been investigated by 2022 is seems.
(wiki-TODO: Investigate whether actuation by pressure has been investigated in the context of foldamer technology.)

There where some proposals in conjunction with the now long outdated molecular assembler concept of using pistons for actuation of nanorobotics. Potential issues are:

(A) A naive implementation has only one single communication channel and does global broadcasting to all nanomachinery.
(B) Thermal motion fluctuations in actuation may be more pronounced.
The smaller the pistons the less the impacts of the gas/fluid molecules average out.
Though the rotor of an electrostatic motor is also subject to at least one thermal engery packet (1/2*k_BT)?
This statement may be wrong. Stuff to think about.

I short: One will want to link together as much of machine phase as stiffly as possible in order to
get as close down to the theoretical lower limit of (1/2*k_BT) as possible for
the entire fully interlinked machine phase "mechanical circuitry".

Actuators in gem-gum tech

At the level of gem-gum technology:

• crystolecule based electrostatic motors will be able to feature exceptionally high power densities (Source Nanosystems).
• chemomechanical converters – basically specialized molecular mills just for the conversion of energy

Related

• Energy conversion
• Motor-muscle

External links

• Wikipedia: Fermi's golden rule

Actuation by optomechanical conversion

Some suggested light activated molecules on the slides here: [1] (Slide 16 & 17) – 5 August 2015
1) BODIPY FL 2) BODIPY R6G 3) BODIPY TMR 4) BODIPY 581/591 5) BODIPY TR 6) BODIPY 630/650
Related: Wikipedia: BODIPY

Early electrostatic actuation

A demonstration of electrostatic actuation of
self assembled foldamer structures (Structural DNA nanotechnology)
in solution (fast data injection)
– Name of paper: "A self-assembled nanoscale robotic arm controlled by electric fields"
– Authors: "Enzo Kopperger1,*, Jonathan List1,*, Sushi Madhira2, Florian Rothfischer1, Don C. Lamb2,3,4, Friedrich C. Simmel1,4,†"
– Pdf: https://diyhpl.us/~nmz787/pdf/A_self-assembled_nanoscale_robotic_arm_controlled_by_electric_fields.pdf