Imagine an ordinary box filled with an assortment of disorganized Lego pieces. Now, imagine taking that box and constantly shaking it. As you shake the box, you look down into it and realize that the Lego pieces have arranged themselves into various structures. Just by shaking the box, these tiny building blocks have fit their protrusions and crevices together to form new shapes.
This phenomenon — directed self-assembly — occurs in a wide range of constituent molecules. Whether they are macromolecules, proteins, colloids, or nanoparticles, these constituent molecules can arrange themselves into structures, such as spheres, ellipsoids and a host of other arrangements that could be potentially useful. Simply applying an external force can introduce interactions within the system of these particles to make them spontaneously assemble into certain structures.The external force used can vary widely as well, and can include electric and magnetic fields.
For example, take the directed self-assembly of magnetic particles under the influence of magnetic fields. When no external force is applied, these particles move randomly as dictated by Brownian motion (random thermal movement of particles suspended in fluid). This is akin to the box of disorganized Lego pieces. However, when an external magnetic field is applied to the particles, they rearrange themselves along the field lines into unique structures — similar to how shaking the box arranges the Lego blocks into structures. The ability to fine-tune these interactions can allow scientists to create a wide array of structures and functions by simply turning on a magnetic field.
The applications for directed self-assembly are endless. As the functionality of nanomaterials increases, the need to be able to synthesize them in profitable way also becomes an important issue. Directed self-assembly offers a low-cost, functional and large-scale method of fabricating these nanomaterials. Advances in technology have created nanomaterials capable of addressing global needs in the diverse areas of medicine, energy production, energy storage, separations, catalysis and data storage; directed self-assembly unlocks this potential so that it can be harnessed in a greater fashion. Instead of having to invest billions for new fabrication equipment each time a new advance is made with nanoscale semiconductors, for example, directed self-assembly allows manufacturing at a low cost and in a functional (possessing the ability to be scaled up) way. With directed self-assembly, the obstacles to unlocking the potential of nanotechnologies are removed.