This video shows the self-assembly of molecules called pyrenes. In the video, three pyrene molecules come together and stack one on top of the other. The world is a sticky place at the nano-scale. When molecules come close to one another, they tend to stick together through something known as 'weak interactions' and this is one way that molecules can self assemble.

In this case, even though the molecules are stuck together, they can slip along each other - think of a magnet stuck on a refrigerator door: it's hard to pull the magnet away from the door but it's easy to slide it on the door.

Ph.D. Student
Biomedical Engineering

If you make sheet out of the pyrene structure you get something called graphene and when graphene stacks up like in the video, you get graphite - the stuff that makes up pencil lead!

So how can we take advantage of self these assembled molecules? Most slippery stuff is wet, right? But what if you want to lubricate something without getting it wet? Well it turns out that when graphene self assembles to make graphite, since the graphene sheets slide along each other this lets you make a dry lubricant! Check out this second video of graphite self-assembling!

Scientists use this idea of self-assembly to help make nanoscale devices. One type of molecule that can self assemble is called an alkane thiol. There is a sulfur (thiol) group on one end and a long hydrophobic tail on the other. Having a hydrophobic tail means that the tail part of the molecule doesn't like water. When a solution of these molecules are squirted on to gold, they self-assemble to form a thin layer. This is because the sulfur group is attracted to the gold and the hydrophobic tails pack together to push away the water in the solution. When they are done self-assembling, the layer is only one molecule deep. It is called a self-assembled monolayer. If we use a very powerful microscope we can see a self-assembled monolayer.

How can we see how this self-assembly process works? One way is through simulations, like the one shown on the right. Powerful computer simulations can calculate all the forces that make molecules self assemble, and show the assembly process in slow motion. The molecules move around in the solution, and over time, they become attracted to the surface and spontaneously organize into a self-assembled monolayer.

Assistant Professor
College of Nanoscale Science and Engineering
University at Albany