Molecular self-assembly is the process by which nanoparticles come together in a defined arrangement– with no assistance.
Self-assembly can be either intramolecular (it happens within one molecule) or intermolecular (two or more molecules involved).Commonly, the term molecular self-assembly refers to intermolecular self-assembly. Intramolecular assembly is usually referred to as folding.
Self-assembly can also occur spontaneously in a solution: the way that a group of soap molecules can “clump together” into an ordered group of molecules known as micelles or as a bilayer.
Figure 6.1 A micelle formed by soap molecules suspended in water
Figure 6.2 A bilayer formed by soap molecules
In both cases the “tails” of the molecules being non-polar are attracted and repelled from the polar solvent but the “heads” of molecule, being ionic, are attracted to the polar solvent.
Diagrams adapted from Mariana Ruiz Villarreal, LadyofHats (Own work) [Public domain], via Wikimedia Commons