Stiffness

 the less soft the nanomachinery the less imprecise the mechanosynthesis


Gradually introducing sufficient stiffness into atomically precise structures is of key importance for bootstrapping the far term goal of advanced nanofactories through a series of earlier increasingly more powerful atomically precise productive nanosystems.

Sufficient stiffness (more precisely: lattice scaled stiffness) is:

• necessary for sufficient suppression of thermal vibration amplitudes.
First sufficiently below the size of pre-produced atomically precise blocks and self-alignment/self-centering slots.
Later sufficiently below atom to atom distance to exponentially suppress misplacement errors.
• necessary to archive atomically precise positioning capability not just topological atomic precision
• necessary for making force applying mechanosynthesis possible
• one reason for the choice of gemstone like compounds as good base material / far term target material

Sufficient lattice scaled stiffness for early low stiffness systems

Usage of self assembled atomically precise base parts (aka "vitamins") allow for less stringent conditions on stiffness.
Only the lattice scaled stiffness must be sufficient for block based self centering assembly (which is not really callable "mechanosynthesis" yet).

How stiffness scales with size

The scaling law for stiffness is such that smaller structures have lower stiffness ("softer"). (wiki-TODO: Add math and graph.) Nanoscale diamond e.g. has a compliance that when interpreted at the macroscale lies in a very intuitively understandable range.
(See: The feel of atoms#Softness)

Main page: Lower stiffness of smaller machinery

Influence of stiffness on manipulator design

The choice of geometric design of nano-manipulators must be taken such that the compliance of the material is compensated for. Long skinny serial mechanics robotic arms (like many industry robots on the macroscale) are a bad choice for the deep nanoscale. Bulky parallel mechanic manipulators are a good choice.

This may be mostly an issue for molecular mills in assembly level 1.

Influence of stiffness on friction

More stiffness causes less or harder to excite degrees of freedom for thermal motion.
This allow for lower levels of friction.
See: Friction in gem-gum technology

The limit to zero stiffness in early systems

Unfolded foldamers basically have zero stiffness (or rather the concept of stiffness breaks down) due to
their chains of single bonds allowing for quite unconstrained freedom of rotation.

They can attain stiffness when they fold up though by formation of internal bonds like
hydrogen bonds, dative bonds, Van der Waals bonds, and sometimes even covalent crosslinking bonds.
Some for this property optimized de-novo proteins can attain quite significant stiffness.

Structural DNA nanotechnology is an interesting case. Even after assembly locally there is practically zero stiffness. On a larger scale there is stiffness albeit quite low one.

Consequences of this include:

General

• The SI unit of stiffness is newtons per square meter (N/m2)
• The inverse of stiffness is called compliance. Not softness which would be the inverse of hardness.