Self-assembly
The term self-assembly (English self-assembly ), has not yet been defined in a uniform and is therefore defined very differently in diverse contexts. This is accompanied by the addition unclear distinction from the term self-organization, so that the use of both terms interchangeably and often occurs nonspecific. For the following definition and classification definitions are taken from the scientific literature and partially extended so that a clear and unambiguous definition is possible.
Definition
The term self-assembly refers to processes of structure and pattern formation, autonomously, ie without external influences such as directing by human intervention, expire. Compared with terms such as formation, training or templating ( German: about matrix-assisted matrix- directed assembly ) in which only processes are combined, the external impact on a system and thus on external information from the environment characterize certain shapes or patterns, the term is self-assembly defined by the following criteria:
- The process goes to existing, separate components (e.g., molecules).
- The result is a product of the information here are the individual components themselves contain (eg, charge, mass, shape, surface properties ) and determines their mutual interactions.
In anglistischen space we distinguish the two processes " self-assembly " and "self- organization" that is " self-assembly " and " self-organization". During self-organization describes the formation of non-equilibrium structures ( no thermodynamic minimum structures ), which describes the formation of self-assembly thermodynamic minimum structures. In the literature, this definition is not always clearly observed, so that - although the clear definition - both terms are used heavily mixed. At the same time especially in biological systems often occurs on a combination of both mechanisms. Examples of self-organization is the actin polymerization to actin filaments ( ATP is necessary ) that holds the structure formation is unbalanced. Self-assembly is for example observed upon crystallization, said ions are assembled on the thermodynamic minimum crystal structure.
Classification
After this conceptual definition of a classification can also be made into various types of self-assembly (based on where there is no different between the definition of parent and complex systems, so that here the definition of the aspect of symmetry has been added):
- Static self-assembly: Symmetrical structures that take a global or local thermodynamic equilibrium.
- Dynamic self-assembly: Ordered structures in systems with dissipative structure, ie, the symmetrical structure can be maintained only by absorbing energy.
- Matrix-assisted self-assembly: the structure is not solely determined by the interactions between the components, but also by regular patterns in the environment of the system (eg structure of a crystal surface ).
Is of great importance for a technological utilization of self-assembly is the ability to affect the selection or design of the components and their interaction so that the result of the self-assembly. In relation to nanotechnologies are used as components of atoms, molecules or nanoparticles into consideration, in particular for molecules due to the possibility of chemical designs a large margin of variability of the interactions is accessible. Join molecules as components in appearance is sometimes the term used in molecular self-assembly publications (eg ), without distinguishing between molecular and supramolecular associations. To take this difference into consideration, the following differentiation can be made:
- Molecular self-assembly: molecules combine to form a covalent structure, but with a certain degree of reversibility of the compounds is given in the formation of the aggregate. This is, for example, to macropolycyclic structures such as porphyrins and phthalocyanines.
- Supramolecular self-assembly: molecules spontaneously associate through non- covalent interactions (eg hydrogen bonds, van der Waals interactions ) to reversible systems. These include, for example, organic films or cell membranes.
Definition to the term self-organization
As with these definitions, the term self-assembly is relatively narrowly tailored, it also arises a possibility of demarcation to the term self-organization. This is useful if autonomous structure-forming processes are considered under the aspect of complexity: Processes that lead to a complexity of development, can be separated from those without complexity and development associate as conceptually distinct.
To make complexity in principle measurable size detectable, so that a clear statement about their change is possible, it can be defined as a measure of how much information is needed at least on the state of a process to predict its future behavior can (so-called statistical complexity).
Based on this definition, a process can be considered as self-organizing, if the statistical complexity increases as a function of time.
Pure self-assembly could be so clearly separate the light of all the above features by the lack of complexity of training and development of self-organization: If caused by self-assembly systems, the information about one of the elements simultaneously allows the prediction of the behavior and the position of all other elements, since it is highly ordered associations that form symmetries. In contrast, let broken symmetries that are not yet chaotic, however, complexity: The information alone over part of the structure is not sufficient to predict the properties and behavior of other parts. Complexity as a feature of self-organization forms and develops between order and disorder - the border region to chaos ( edge of chaos ), which arises for example when removing systems from thermodynamic equilibrium and thereby caused instabilities.