Self-assembly

At the nanoscale, things are different. Think about your room at home. If you don’t work at putting stuff away, things become a mess. At the nanoscale sometimes things arrange themselves. This is a process called ‘self-assembly’. Molecules sometimes self-assemble, like soap forming a bubble when you blow air through a soapy loop. The soap molecules spontaneously form a bubble because they interact in a special way when they are around a lot of air and little bit of water. Soap bubbles are made from micelles, the molecules form a thin layer that then becomes a ball. So at the nanoscale, molecules sometimes self-assemble but only when the environment is also right.

Scientists use self-assembly to help make nanoscale devices. Molecules called ‘alkane thiols’ will self assemble. They have a sulfur (the thiol) group on one end and then have a long hydrophobic tail much like a lipid. Remember that hydrophobic means it hates water and lipids don’t like water. These molecules self-assemble to form a very thin layer when a solution of them in water is squirted on to gold. That is because the sulfur group is attracted to the gold and then long hydrophobic tails pack together to push away the water. When they finish self-assembling they form a layer that 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.

We can see the self-assembly process using simulations. Simulations are done on computers and all of the forces that make molecules self-assemble are calculated. If you watch this simulation you will see the molecules self-assemble on a surface of gold. The molecules move around and over time they are attracted to the surface.  As they begin to pack the surface, they organize because of the interactions between the long hydrophobic tails. This all happens spontaneously, it is fabrication without tools.