Another important class of self-assembly is field-directed assembly. An example of this 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.
Regardless of the mechanism driving self-assembly, people take self-assembly approaches to materials synthesis to avoid the problem of having to construct materials one building block at a time. Avoiding one-at-a-time approaches is important because the amount of time required to place building blocks into a target structure is prohibitively difficult for structures that have macroscopic size.
Once materials of macroscopic size can be self-assembled, those materials can find use in many applications. For example, nano-structures such as nano-vacuum gaps are used for storing energy  and nuclear energy conversion. At this point, one may argue that any chemical reaction driving atoms and molecules to assemble into larger structures, such as precipitation , could fall into the category of self-assembly. However, there are at least three distinctive features that make self-assembly a distinct concept.
First, 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. This is generally not true in chemical reactions , where an ordered state may proceed towards a disordered state depending on thermodynamic parameters. The second important aspect of self-assembly is the predominant role of weak interactions e.
These weak interactions are important in materials synthesis for two reasons. First, weak interactions take a prominent place in materials, especially in biological systems. For instance, they determine the physical properties of liquids, the solubility of solids, and the organization of molecules in biological membranes. Second, in addition to the strength of the interactions, interactions with varying degrees of specificity can control self-assembly. Self-assembly that is mediated by DNA pairing interactions constitutes the interactions of the highest specificity that have been used to drive self-assembly.
The third distinctive feature of self-assembly is that the building blocks are not only atoms and molecules, but span a wide range of nano- and mesoscopic structures, with different chemical compositions, functionalities,  and shapes. Examples also included microparticles with complex geometries, such as hemispherical,  dimer,  discs,  rods, molecules,  as well as multimers. These nanoscale building blocks can in turn be synthesized through conventional chemical routes or by other self-assembly strategies such as Directional Entropic Forces.
More recently, inverse design approaches have appeared where it is possible to fix a target self-assembled behavior, and determine an appropriate building block that will realize that behavior. Self-assembly in microscopic systems usually starts from diffusion, followed by the nucleation of seeds, subsequent growth of the seeds, and ends at Ostwald ripening.
The thermodynamic driving free energy can be either enthalpic or entropic or both. The growth rate is the competition between these two processes. Important examples of self-assembly in materials science include the formation of molecular crystals , colloids , lipid bilayers , phase-separated polymers , and self-assembled monolayers. Recently, the three-dimensional macroporous structure was prepared via self-assembly of diphenylalanine derivative under cryoconditions, the obtained material can find the application in the field of regenerative medicine or drug delivery system.
Chen et al. This self-assembly method can be used for generation of diverse sets of symmetrical and periodic patterns from microscale materials such as hydrogels , cells, and cell spheroids. Self-assembly extends the scope of chemistry aiming at synthesizing products with order and functionality properties, extending chemical bonds to weak interactions and encompassing the self-assembly of nanoscale building blocks at all length scales.
In self-assembling structures, the scientist must predict this minimum, not merely place the atoms in the location desired. Another characteristic common to nearly all self-assembled systems is their thermodynamic stability. For self-assembly to take place without intervention of external forces, the process must lead to a lower Gibbs free energy , thus self-assembled structures are thermodynamically more stable than the single, unassembled components. A direct consequence is the general tendency of self-assembled structures to be relatively free of defects. An example is the formation of two-dimensional superlattices composed of an orderly arrangement of micrometre-sized polymethylmethacrylate PMMA spheres, starting from a solution containing the microspheres, in which the solvent is allowed to evaporate slowly in suitable conditions.
In this case, the driving force is capillary interaction, which originates from the deformation of the surface of a liquid caused by the presence of floating or submerged particles. These two properties—weak interactions and thermodynamic stability—can be recalled to rationalise another property often found in self-assembled systems: the sensitivity to perturbations exerted by the external environment. These are small fluctuations that alter thermodynamic variables that might lead to marked changes in the structure and even compromise it, either during or after self-assembly.
The weak nature of interactions is responsible for the flexibility of the architecture and allows for rearrangements of the structure in the direction determined by thermodynamics. If fluctuations bring the thermodynamic variables back to the starting condition, the structure is likely to go back to its initial configuration.
This leads us to identify one more property of self-assembly, which is generally not observed in materials synthesized by other techniques: reversibility. Self-assembly is a process which is easily influenced by external parameters. This feature can make synthesis rather complex because of the need to control many free parameters. Yet self-assembly has the advantage that a large variety of shapes and functions on many length scales can be obtained. The fundamental condition needed for nanoscale building blocks to self-assemble into an ordered structure is the simultaneous presence of long-range repulsive and short-range attractive forces.
By choosing precursors with suitable physicochemical properties, it is possible to exert a fine control on the formation processes that produce complex structures. Clearly, the most important tool when it comes to designing a synthesis strategy for a material, is the knowledge of the chemistry of the building units. For example, it was demonstrated that it was possible to use diblock copolymers with different block reactivities in order to selectively embed maghemite nanoparticles and generate periodic materials with potential use as waveguides.
In it was proposed that every self-assembly process presents a co-assembly, which makes the former term a misnomer.
This thesis is built on the concept of mutual ordering of the self-assembling system and its environment. The most common examples of self-assembly at the macroscopic scale can be seen at interfaces between gases and liquids, where molecules can be confined at the nanoscale in the vertical direction and spread over long distances laterally. Examples of self-assembly at gas-liquid interfaces include breath-figures , self-assembled monolayers and Langmuir—Blodgett films , while crystallization of fullerene whiskers is an example of macroscopic self-assembly in between two liquids.
Self-assembly processes can also be observed in systems of macroscopic building blocks. These building blocks can be externally propelled  or self-propelled. For some systems, the components' interaction preferences are programmable.
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The self-assembly processes can be easily monitored and analyzed by the components themselves or by external observers. In April , a 3D printed plastic was combined with a "smart material" that self-assembles in water,  resulting in " 4D printing ". People regularly use the terms " self-organization " and "self-assembly" interchangeably. As complex system science becomes more popular though, there is a higher need to clearly distinguish the differences between the two mechanisms to understand their significance in physical and biological systems.
Both processes explain how collective order develops from "dynamic small-scale interactions". Self-assembly requires components to remain essentially unchanged throughout the process. Besides the thermodynamic difference between the two, there is also a difference in formation. The first difference is what "encodes the global order of the whole" in self-assembly whereas in self-organization this initial encoding is not necessary.
However, this does not take into account the essential role of energy in driving biochemical reactions in cells.
Self-assembly - Wikipedia
The systems of reactions in any cell are self-catalyzing but not simply self-organizing as they are thermodynamically open systems relying on a continuous input of energy. Phenomena from mathematics and computer science such as cellular automata , random graphs , and some instances of evolutionary computation and artificial life exhibit features of self-organization. In swarm robotics , self-organization is used to produce emergent behavior.
In particular the theory of random graphs has been used as a justification for self-organization as a general principle of complex systems. In the field of multi-agent systems , understanding how to engineer systems that are capable of presenting self-organized behavior is an active research area. If the solution is considered as a state of the iterative system, the optimal solution is the selected, converged structure of the system. These emerge from bottom-up interactions, unlike top-down hierarchical networks within organizations, which are not self-organizing.
Norbert Wiener regarded the automatic serial identification of a black box and its subsequent reproduction as self-organization in cybernetics. Eric Drexler sees self-replication as a key step in nano and universal assembly. By contrast, the four concurrently connected galvanometers of W. Ross Ashby 's Homeostat hunt , when perturbed, to converge on one of many possible stable states. Nyquist stability criterion. Warren McCulloch proposed "Redundancy of Potential Command"  as characteristic of the organization of the brain and human nervous system and the necessary condition for self-organization.
In the s Stafford Beer considered self-organization necessary for autonomy in persisting and living systems. He applied his viable system model to management. It consists of five parts: the monitoring of performance of the survival processes 1 , their management by recursive application of regulation 2 , homeostatic operational control 3 and development 4 which produce maintenance of identity 5 under environmental perturbation.
Focus is prioritized by an alerting "algedonic loop" feedback: a sensitivity to both pain and pleasure produced from under-performance or over-performance relative to a standard capability. In the s Gordon Pask argued that von Foerster's H and Hmax were not independent, but interacted via countably infinite recursive concurrent spin processes  which he called concepts.
His strict definition of concept "a procedure to bring about a relation"  permitted his theorem "Like concepts repel, unlike concepts attract"  to state a general spin-based principle of self-organization. His edict, an exclusion principle, "There are No Doppelgangers " means no two concepts can be the same. After sufficient time, all concepts attract and coalesce as pink noise. The theory applies to all organizationally closed or homeostatic processes that produce enduring and coherent products which evolve, learn and adapt.
The self-organizing behaviour of social animals and the self-organization of simple mathematical structures both suggest that self-organization should be expected in human society. Tell-tale signs of self-organization are usually statistical properties shared with self-organizing physical systems. Examples such as critical mass , herd behaviour , groupthink and others, abound in sociology , economics , behavioral finance and anthropology. In social theory, the concept of self-referentiality has been introduced as a sociological application of self-organization theory by Niklas Luhmann For Luhmann the elements of a social system are self-producing communications, i.
For Luhmann human beings are sensors in the environment of the system. Luhmann developed an evolutionary theory of Society and its subsystems, using functional analyses and systems theory. In economics, a market economy is sometimes said to be self-organizing. Paul Krugman has written on the role that market self-organization plays in the business cycle in his book "The Self Organizing Economy". Neo-classical economists hold that imposing central planning usually makes the self-organized economic system less efficient. On the other end of the spectrum, economists consider that market failures are so significant that self-organization produces bad results and that the state should direct production and pricing.
Most economists adopt an intermediate position and recommend a mixture of market economy and command economy characteristics sometimes called a mixed economy. When applied to economics, the concept of self-organization can quickly become ideologically imbued. Enabling others to "learn how to learn"  is often taken to mean instructing them  how to submit to being taught.
Self-organised learning S. The self-organizing behavior of drivers in traffic flow determines almost all the spatiotemporal behavior of traffic, such as traffic breakdown at a highway bottleneck, highway capacity, and the emergence of moving traffic jams. In — these complex self-organizing effects were explained by Boris Kerner 's three-phase traffic theory. Order appears spontaneously in the evolution of language as individual and population behaviour interacts with biological evolution.
Self-organized funding allocation SOFA is a method of distributing funding for scientific research.
In this system, each researcher is allocated an equal amount of funding, and is required to anonymously allocate a fraction of their funds to the research of others. Proponents of SOFA argue that it would result in similar distribution of funding as the present grant system, but with less overhead. Most scientists would agree with the critical view expressed in Problems of Biological Physics Springer Verlag, by the biophysicist L. Blumenfeld, when he wrote: "The meaningful macroscopic ordering of biological structure does not arise due to the increase of certain parameters or a system above their critical values.
These structures are built according to program-like complicated architectural structures, the meaningful information created during many billions of years of chemical and biological evolution being used. Of course, Blumenfeld does not answer the further question of how those program-like structures emerge in the first place.
His explanation leads directly to infinite regress. In short, they [Prigogine and Stengers] maintain that time irreversibility is not derived from a time-independent microworld, but is itself fundamental. The virtue of their idea is that it resolves what they perceive as a "clash of doctrines" about the nature of time in physics. Most physicists would agree that there is neither empirical evidence to support their view, nor is there a mathematical necessity for it. There is no "clash of doctrines. In theology , Thomas Aquinas — in his Summa Theologica assumes a teleological created universe in rejecting the idea that something can be a self-sufficient cause of its own organization: .
Since nature works for a determinate end under the direction of a higher agent, whatever is done by nature must needs be traced back to God, as to its first cause. So also whatever is done voluntarily must also be traced back to some higher cause other than human reason or will, since these can change or fail; for all things that are changeable and capable of defect must be traced back to an immovable and self-necessary first principle, as was shown in the body of the Article.
From Wikipedia, the free encyclopedia. It has been suggested that Spontaneous order be merged into this article. Discuss Proposed since May Further information: Spontaneous order. See also: Self-assembly and Self-assembly of nanoparticles. Further information: Biological organisation.
Main article: Self-organization in cybernetics. Main article: Spontaneous order. Main article: Three-phase traffic theory. Autopoiesis Autowave Self-organized criticality control Free energy principle Information theory Constructal law Emergence. Journal of Materials Chemistry A. International Journal of Signs and Semiotic Systems.
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Self-organization in Biological Systems. Princeton studies in complexity reprint ed. Princeton University Press. Retrieved Cellular Automata: A Discrete Universe. World Scientific. Self-organization and Emergence in Life Sciences.
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