Revision as of 15:34, 5 January 2014

Diamondoid molecular elements (DMEs) are structural elements or machine elements at the lower physical size limit. They often are highly symetrical. Since metals are unsuitable (they lack directed bonds and tend to diffuse) diamondoid materials must be used.

• DM machine elements (DMMEs) (examples) like bearigs and gears have completely passivated surfaces.
• DM structural elements (DMSEs) (example) are minimally sized structural building blocks that are only partially passivated. They expose multiple radicals on some of their surfaces that act as AP welding interfaces to complementary surfaces. The step of connecting surface interfaces is done in assembly level II and is irreversible.

Name suggestion: since DMEs are somewhat of a cross between crystals and molecules why not call them "crystolecules"

• DME ... Diamodoid Molecular Element (stiff - small - minimal)
• DMME ... D.M. Machine Element
• DMSE ... D.M. Structural Element

Diamondoid molecular machine elements

Images of some examples.

Types

Bearings

[Todo: describe incommensurate superlubrication & pullout bearing effect & "binary" effect]

Fasteners

[Todo: describe locking mechanisms: hierarchical; barrier; difference to makro; covaconn;...]

Others

[Todo: gears, pumps, telescoptc rods .... DME issues lack of ball curvature & DMSEs?]

Sets

Minimal set of compatible DMMEs

In electric circuits there is one topological and three kinds of basic passive elements.
Adding an active switching element one can create a great class of circuits.
0) fork node; 1) capacitors; 2) inductors; 3) resistors

Those passive elements have a direct correspondences in rotative or reciprocating mechanics namely:
0) planetary or differential gearbox [*]; 1) springs; 2) inertial masses; 3) friction elements
[*] and analogons for reciprocating mechanics

But there are limits to the electric-mechanic analogy. Some mechanic elements often differ significantly from their electric counterparts in their qualitative behavior. Two examples of elements quite different in behaviour are:

• transistors & locking pins
• transformers & gearboxes

With creating a set of standard sizes of those elements and a modular building block system to put them together creating rather complex systems can be done in a much shorter time.
Like in electronics one can first create a schematics and subsequently the board.

To do: Create a minimal set of minimal sized DMMEs for rotative nanomechanics. Modular housing structures standard bearings and standard axle redirectioning are also needed.

To investigate: how can reciprocating mechanics be implemented considereng the passivation bending issue

Diamondoid molecular structural elements

An example of a diamondoid molecular structural element (DMSE). The bright red spots are open bonds.

sets

[Todo: describe standardized building block systems]

General properties

DMEs with carbon, silicon carbide or silicon as core material can be can have internal structure like

• diamond / lonsdaleite
• or other possibly strained sp³ configurations.

Due to the lack of defects the ultimate tensile strength of larger DMEs lies above diamond of thermodynamic origin.

Forces from compressive and tensile stresses

It can be helpful or at least satisfying to get something of an intuitive understanding for the consistence or "feel" of DME components.

As the size of a rod of any material shrinks linearly (in all three dimensions) the area of the cross section shrinks quadratically. Consequently when keeping tension/compression stress constant the forces fall quadratically and one arrives at very low forces. [Sacling law: longitudinal force ~ length^2] This can be seen nicely in the low seeming inter-atomic spring constants. E.g. the equilibrium position spring constant of an bond in diamond (sp3 carbon-carbon-bond) is about 440nN/nm or 0.44daN/cm (1daN~1kg).

In order to get a feel for these forces one can transform atomic spring constants unchanged to the macrocosm. This can be done by letting the number of parallel and serial bonds grow equally so that the changement of stiffness through serial and parallel connection of bonds compensate. Here for convenience 10,000,000,000 bonds are assumed to be chained serially. We must apply this scaling to the number of parallel bonds too but here it divides up in each dimension of the cross-section sqrt(10^10) = 100,000. With the diamond bond (C-C sp3) length of 1.532Amstrong and area per bond of 6.701Amstrong^2 = (2.59Amstrong)^2 one gets a diamond string (with square cross-section) of 1.532m length and 25.9um thickness side to side (half a hair) that retains the atomic spring constant of 440N/m or 0.44daN/cm (1daN~1kg) If you bind up a half liter bottle of water with that (somewhat dangerous knife like) string it will bend around 1cm.

Putting one end of the sting in a vacuum filled square piston that seals tightly shows how little effect everyday pressures have at the micro and nanocosmos. Taking 1bar = 10^5N/m^2 ambient pressure the string experiences a force of only 67.1µN and elongates 0.152µm an invisible amount.

Though as seen bonds are rather compliable DMEs are still hard diamond since hardness is closely related to tensile and compressive stress which is scale invariant. The small force representation of high pressures might be a bit counterintuitive and hard to grasp.

By making the compliance at the nanolevel experiencable the model with the weight on the one bond equivalent diamond string should make one (maybe obvious) practical thing clear. That it is very effective to focus forces.

In mechanosynthesis conical tips can easily focus forces down to a more compliable size level. Not much of a size difference is needed. Nanoscale manipulators in the machine phase can hold back on their supporting structures they're mounted to. It is easy to create DMEs with high internal strains such as strained shell cylindrical structures, press fittings, structures under high tensile stress and more. Great amounts of elastic energy can be stored (permanently or temporarily).

Example of safely usable pressures from Nanosystems section 2.3.2.: Assuming ~1% strain the required stress is ~1% of diamonds young modulus. 10nN/nm^2 = 10GPa = 1000daN/mm^2 (1daN~1kg) this is 20% of the tensile strength of macro-scale diamond with natural flaws. Flawless mechanosynthetically assembled diamond will be capable of handling more stress.

[Todo: add info about shearing stress]

Surfaces

When viewing the thickness of a surface as the distance from the point of maximally attractive VdW force to the point of equally repulsive VdW force (experienced by some probing tip) the thickness of the surface relative to the thickness of the diamondoid part is enormous. This makes DMEs somewhat soft in compressibility but not all that much as can be guessed by the compressibility of single crystalline graphite which is a stack of graphene sheets.

[Todo: add further relevant scaling laws & example calculation]

VdW sticking

[Todo: add calculation of how much surface is needed to securely overcome the characteristic thermal energy]

Acceleration tolerance

[Todo: add calculation of a block on a neck model]