Bottom-up fabrication: Self-Assembly

A key approach in the bottom-up fabrication technique is the self-assembly. Self-assembly in the classic sense can be defined as the spontaneous and reversible organization of molecular units into ordered structures by non-covalent interactions. The first property of a self-assembled system that this definition suggests is the spontaneity of the self-assembly process - the interactions responsible for the formation of the self-assembled system act on a strictly local level, or in other words, the nanostructure builds itself.

There are at least three distinctive features that make self-assembly a distinct concept:

Order

The self-assembled structure must have a higher order than the isolated components, be it a shape or a particular task that the self-assembled entity may perform.

Interactions

Self-assembled structures rely on slack interactions (e.g. Van der Waals, capillary, hydrogen bonds) with respect to more "traditional" covalent, ionic, or metallic bonds. Although typically less energetic by a factor of 10, these weak interactions play an important role in materials synthesis. It can be instructive to note how slack interactions hold a prominent place in materials, but especially in biological systems, although they are often considered marginal when compared to strong (i.e. covalent, etc.) interactions.

Building blocks

The building blocks are not only atoms and molecules, but span a wide range of nano- and mesocopic structures with different chemical compositions, shapes and functionalities. These nanoscale building blocks can in turn be synthesized through conventional chemical routes or by other self-assembly strategies.

There are two types of self-assembly: intramolecular self-assembly and inter-molecular self-assembly. Intramolecular self-assembling molecules are often complex polymers with the ability to assemble from the random coil conformation into a well-defined stable structure (secondary and tertiary structure). An example of intramolecular self-assembly is protein folding. Intermolecular self-assembly is the ability of molecules to form supramolecular assemblies (such as quaternary structure). A simple example is the formation of a micelle by surfactant molecules in solution.

Following is short video that demonstrates the self-assembly: