Self-assembly

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Self-assembly is the fundamental principle which generates structural organization on all scales from molecules to galaxies. It is defined as reversible processes in which pre-existing parts or disordered components of a preexisting system form structures of patterns. Self-assembly can be classified as either static or dynamic. Static self-assembly is when the ordered state occurs when the system is in equilibrium and does not dissipate energy. Dynamic self-assembly is when the ordered state requires dissipation of energy. Examples of self-assembling system include weather patterns, solar systems, histogenesis and self-assembled monolayers. The most well-studied subfield of self-assembly is molecular self-assembly, but in recent years it has been demonstrated that self-assembly is possible with micro and millimeterscale structures lying in the interface between two liquids.

[edit] Molecular self-assembly

Molecular self-assembly is the assembly of molecules without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly, although in some books and articles the term self-assembly refers only to intermolecular 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 (quarternary structure). A simple example is the formation of a micelle by surfactant molecules in solution.

Self-assembly can occur spontaneously in nature, for example in cells (such as the self-assembly of the lipid bilayer membrane) and other biological systems, as well as in human engineered systems such as a Langmuir monolayer. It usually results in the increase in internal organization of the system. Biological self-assembling systems, including synthetically engineered self-assembling peptides and other biomaterials, have been shown to have superior handling, biocompatibility and functionality. These advantages are due directly to self-assembly from biocompatible precursors creating biomaterials engineered at the nano-scale.

Also, self-assembly is a manufacturing method used to construct things at the microscale, which is comprised of structures with at least one dimension that is less than 100microns. Many biological systems use self-assembly to assemble various molecules and structures. Imitating these strategies and creating novel molecules with the ability to self-assemble into supramolecular assemblies is an important technique in nanotechnology. In self-assembly the final (desired) structure is 'encoded' in the shape and properties of the molecules that are used, as compared to traditional techniques, such as lithography, where the desired final structure must be carved out from a larger block of matter. Self-assembly is thus referred to as a 'bottom-up' manufacturing technique, as compared to lithography being a 'top-down' technique. The synthesis of molecules for self-assembly often involves a chemical process called convergent synthesis. Microchips of the future might be made by molecular self-assembly. An example of self-assembly in nature is the way that hydrophilic and hydrophobic interactions cause cell membranes to self assemble.