Self-assembly

and

beyond

Outline

• What is X?
• Colloidal X
• Nanoscale X
• Beyond X

X = Self-assembly

What is it?

Self-assembly is the formation of structures via the interaction of the constituents.

Most of the time*, self-assembly refers to weakly-interacting components that are able to diffuse and explore configurations until they (may) reach the state of thermodynamic equilibrium.

* Not always, you can have non-equilibrium self-assembly, or modular robots that act deterministically, etc.

Colloidal SA

What? Colloidal spheres (a few microns in size)

How? Depletion attraction. Microparticles surrounded by nanoparticles. When microparticles come close, nanoparticles don't fit in between and entropy then favours microparticles to stick together so that nanoparticles have more free volume to explore

What do we see?

Clusters form that are free energy minima.

Free energy proportional to number of connections.

Therefore minima = maximum number of connections.

BUT, there are many structures with the same number of connections.

Enumerating them turns out to be surprisingly hard. Need computers' help.

Can we program this?

Yes.

Use DNA coating.

But there are limits

Nanoscale SA

i.e. shrink by 1000

What? DNA

How? Watson-Crick base pairing

DNA Origami

DNA Origami

Also variant called DNA bricks, doesn't need base single strand

3D DNA origami

Functional DNA structures (machines)

Problems with self-assembly

• Slow (hours, days, weeks, depending)
• Inefficient (low yield, specially for large or complex structures).

Beyond self-assembly

Beyond Equilibrium -> Non-equilibrium self-assembly. Active matter, pattern formation

Hierarchical self-assembly -> Build small building blocks, then put them together, and so on

Direct assembly:

• Guided/patterned assembly
• Build a better tool to help you assemble (life does it with ribosomes)

A Nano 3D printer?

Watch Eric Drexler's presentation on the Oxford Martin School website for more.