Self-assembly

Self-assembly is a process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction. When the constitutive components are molecules, the process is termed molecular self-assembly. Self-assembly is a process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of specific, local interactions among the components themselves, without external direction. When the constitutive components are molecules, the process is termed molecular self-assembly. Self-assembly can be classified as either static or dynamic. In static self-assembly, the ordered state forms as a system approaches equilibrium, reducing its free energy. However, in dynamic self-assembly, patterns of pre-existing components organized by specific local interactions are not commonly described as 'self-assembled' by scientists in the associated disciplines. These structures are better described as 'self-organized', although these terms are often used interchangeably. 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—in other words, the nanostructure builds itself. Although self-assembly typically occurs between weakly-interacting species, this organizaiton may be transfered into strongly-bound covalent systems. An example for this may be observed in the self-assembly of polyoxometalates. Evidence suggests that such molecules assemble via a dense-phase type mechanism whereby small oxometalate ions first assemble non-covalently in solution, followed by a condensation reaction that covalently binds the assembled units. This process can be aided by the introduction of templating agents to control the formed species. In such a way, highly organized covalent molecules may be formed in a specific manner. Self-assembled nano-structure is an object that appears as a result of ordering and aggregation of individual nano-scale objects guided by some physical principle. Self-assembled nanostructure arises in the strong non-equilibrium conditions. The most famous example of self-assembly phenomenon is the occurrence of the life on Earth. It is plausible to hypothesize that it happens because the sun generates a strong temperate gradient in its environment. This general idea has been confirmed in the experiment of self-assembly of carbon nanotubes. Another interesting example of self-assembly is the phenomenon of electrostatic trapping. In this case an electric field is applied between two metallic nano-electrodes. The particles present in the environment are polarized by the applied electric field. Because of dipole interaction with the electric field gradient the particles are attracted to the gap between the electrodes. Fabricating a crystal by placing atom after atom is not realistic. However self-assembly of crystals works well. Similarly fabricating a 3D nano-structure is not realistic as well. Self-assembly of 3D nano-structure becomes an easy and inexpensive way to fabricate them. Nano-structures such as nano-vacuum gaps are used for storing energy and nuclear energy conversion. Self-assembled tunable materials are promising candidates for large surface area electrodes in batteries and organic photovoltaic cells, as well as for microfluidic sensors and filters.