Latest revision as of 09:56, 9 June 2021

(also called: shape locking, positive locking, positive closure, form closure ...)

Usage against thermal Van der Waals bond breakage in the low nanoscale - hirachical locking

When the contacting area of two building blocks is made smaller then they wont stick together as strong as before. If the contacting area gets so low that the Van der Waals bonding energy falls in the range of the energy range of the thermal excitations it becomes likely that connections get knocked open just by chance.

Note that the critical surface area is rather small for room temperature and bulk (hydrogen terminated) diamond. A nice thing is that with linear rising contact area breakage probability for the VdW-bond falls exponentially thus areas that will never break are quickly reached.

Shape locking might be especially important for high temperature applications where small contact areas become insufficient to hold things together.
Although for

• some critical (quite small) contact area
• a given (huge) number of contacts – multiplied by – a given (long) timespan – (ergodic?) time-number-product

thermal excitations will melt the material before even ripping apart the first Van der Waals bond.
So risk of thermal-rip-apart of Van der Vaals bonds might not be relevant at all for all but the very smallest contact areas.
It would rather be a deliberate design choice to keep the contact area ultra low. If even possible. (spiky needle grabbing).

Since there seems to be no special time-number-product this is not a special number but a curve.

TODO (for solid diamond-diamond contact):

• Plot the chance of first-bond-rip over time-number-product for different contact-areas. (shifted falling logistic curve??)
• Plot the contact-area over the time-number-product for different chancces of first-bond-rip?
• Plot the chance of first-bond-rip over over contact-area for given time-number-product?

At small scales more for strength than for holding things together

Given the Van der Waals force is holding things together quite well for assembly purposes in small scales form closure is:

• rather a mean for strength against tensile and shearing loads
• rather than a mean for holding things together temporarily

Form closure becomes increasingly important as a connection mechanism with bigger scales.

• Like dust and dirt can get in the way of Van der Waals force at the macroscale.
• Like mass to surface area rises (and gravitation becoming relevant)

Hierarchical locking

To prevent building blocks from falling apart by accident (maybe only relevant for larger scales) one can chain shape locking together.
Part A can't be removed because part B is in the way. Part B can't be removed because part C is in the way. And so on and so forth.

The only removable element, the last in assembly and first in disassembly (LIFO last in first out) needs to be an energetic energy barrier (generalized clip – energetic locking). Nanoscale this can be Van der Waals force. The energy barrier must be strong enough to reliably withstand thermal fluctuations of the operation temperature. Likely the case.

Used can be:

• Van der Waals sticking with sufficient surface (and back-volume density)
• Clipping - a crystal deformation is needed to open the lock
  (unlike macroscopic gemstones up to ~30% deformation is possible in flawless crystolecules)
  When using clipping either one accepts significant energy loss or one gives the clips a shape that is grabbable.
• Sparsely packed covalent bonds - (only reopenable in practically perfect vacuum)
• Densely packed covalent bonds - (not reopenable at all - see: atomically precise disassembly)

Note that:

• If an energy barrier of the lower levels (a bunch of covalent bonds) is overcome first it leads to a complete destruction of the structure.
• Interfaces could be hierarchically locked with sliding planes. [todo: add info-sketch]

[todo: calculate the amount of reduction in probability of failure (in chained shape locking structures) depending on contact areas and temperatures]

Basic serial chains using shape locking

Examples for possible solutions of this problem (1D structure examples):

• sturdy chain that uses shape locking - leave to thingiverse
• serial hierarchical locking structure - leave to thingiverse

The necessary surface area for energetic locking via VdW sticking may be includable in a distributed form along the whole length of the chain [todo: investigate this].

Assembly forking = Disassembly merging

Note that too long chains make a parallel assembly process impossible. Thus chains should not be made longer than necessary. To reduce that issue in structures (we are deviating from linear chains now) one can include forkings in the shape lock chaining. That is at some point at least two parts need to be removed such that the held part can be removed. This can increasing accessible working spots and speed up both assembly and disassembly. The downside is that one ends up with many open ends that all need energetic locking.

Assembly merging = Disassembly forking

One can merge the shape lock chain such that one ends up with a tree converging topology in the order of assembly. That way one can resort to only one single energetic end lock. Many parallel chains of equal length that contact side by side could be tied together at their ends by turning 90° into single orthogonal chain at their ends. This would make A single 2D sheet. Many of those sheets could be tied together similarly to make a cuboid. To disassemble such a cuboid shaped assembly the process must start at a corner then work down an edge proceed along a surface and finally disassemble the whole volume. The disadvantage is that when starting the disassembly work there is only one point to work on.

Summary

Inclunding both merging and forking one ends up with a directed acyclic graph topology.

At temperatures around room temperature there probably wont be so much necessity of shape locking. [To investigate: How much shape locking is necessary in applications that are going to the limits of diamondoid materials]

There is a need for methods to find an optimum. The product should not resemble a challenging shape lock puzzle but something that is most practical.

Usage in bigger scales

To make assembly reversible with low energy turnover while retaining near full material strength

• Expanding ridge joint
• Recycling

Usage in hierarchies

...

Related

• Form closing interlocking
• Connection method
• Nanoscale connection method

External links

• Remotely related: Wikipedia: Mechanically interlocked molecular architectures (MIMAs)