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| {{other uses|Self-construction (disambiguation)}}
| | Ed is what people contact me and my wife doesn't like it at all. My day occupation is an information officer but I've already utilized for an additional 1. She is really fond of caving but she doesn't have the time lately. Ohio is where his home is and his family loves it.<br><br>Also visit my homepage :: clairvoyants ([http://www.sivuland.biz/pods/show/great-hobby-advice-to-assist-get-you-going sivuland.biz]) |
| [[Image:Selfassembly Organic Semiconductor Trixler LMU.jpg|250px|thumb|STM image of self-assembled [[supramolecular]] chains of the [[organic semiconductor]] [[Quinacridone]] on [[Graphite]]. ]]
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| '''Self-assembly''' is a type of 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]].
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| Self-assembly can be classified as either static or dynamic. In ''static'' self-assembly, the ordered state forms as a system approaches [[Thermodynamic equilibrium|equilibrium]], reducing its [[Thermodynamic free energy|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-organization|self-organized]]".
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| == Self-assembly in chemistry and materials science ==
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| [[Image:DNA nanostructures.png|thumb|250px|The DNA structure at left (schematic shown) will self-assemble into the structure visualized by [[Atomic force microscope|atomic force microscopy]] at right. Image from Strong.<ref>{{cite journal|author=M. Strong|journal=[[PLoS Biology|PLoS Biol.]]|title=Protein Nanomachines|volume=2|issue=3|year=2004|pages=e73–e74|doi=10.1371/journal.pbio.0020073|pmid=15024422|pmc=368168}}</ref>]]
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| Self-assembly (SA) in the classic sense can be defined as ''the spontaneous and [[Reversible reaction|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 [[Emergence#Emergent_properties_and_processes|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''.
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| ===Distinctive features===
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| At this point, one may argue that any chemical reaction driving atoms and molecules to assemble into larger structures, such as [[precipitation (chemistry)|precipitation]], could fall into the category of SA. However, there are at least three distinctive features that make SA a distinct concept.
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| ====Order====
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| First, the self-assembled structure must have a higher [[Order (crystal lattice)|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 reaction]]s, where an ordered state may proceed towards a disordered state depending on thermodynamic parameters.
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| ====Interactions====
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| The second important aspect of SA is the key role of slack interactions (e.g. [[Van der Waals force|Van der Waals]], [[capillary action|capillary]], [[Pi-pi interaction|<math>\pi-\pi</math>]], [[hydrogen bond]]s) with respect to more "traditional" covalent, [[ionic bond|ionic]], or [[metallic bond]]s. Although typically less energetic by a factor of 10, these weak interactions play an important role in materials synthesis. It can be instructive to note how slack interactions hold a prominent place in materials, especially in biological systems, although they are often considered marginal with respect to "strong" (i.e. covalent, etc.) interactions. For instance, they determine the physical properties of liquids, the [[solubility]] of solids, and the organization of molecules in biological membranes.
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| ====Building blocks====
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| The third distinctive feature of SA 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, shapes and functionalities<ref>{{cite web |url=http://arxiv.org/abs/1202.2177 |title=Structural Diversity and the Role of Particle Shape and Dense Fluid Behavior in Assemblies of Hard Polyhedra |accessdate=23 June 2012 |archiveurl=http://arxiv.org/pdf/1202.2177v1.pdf|archivedate = 2012-02-10}}</ref>. Recent examples of novel building blocks include [[tetrahedron packing | polyhedra]] and [[Patchy Particles | patchy particles]]. These nanoscale building blocks (NBBs) can in turn be synthesised through conventional chemical routes or by other SA strategies such as [[Entropic force#Directional Entropic Force|Directional Entropic Forces]].
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| ===Examples===
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| Important examples of SA in materials science include the formation of molecular [[crystal]]s, [[colloid]]s, [[lipid bilayer]]s, [[phase-separated polymer]]s, and [[self-assembled monolayer]]s.<ref>{{cite journal|author=Whitesides, G.M.; Boncheva, M. |title=Beyond molecules: Self-assembly of mesoscopic and macroscopic components|journal= PNAS |year=2002|volume= 99|doi=10.1073/pnas.082065899|pmid=11959929|issue=8|pmc=122665|pages=4769–74}}</ref><ref name="whitesides_2005_science">{{cite journal|year=2005|journal=Science Progress|volume=88|pages=17–48|author=Whitesides, George M.; Kriebel, Jennah K.; Love, J. Christopher|doi=10.3184/003685005783238462|title=Molecular engineering of surfaces using self-assembled monolayers|pmid=16372593|issue=Pt 1}}</ref> The folding of polypeptide chains into proteins and the folding of nucleic acids into their functional forms are examples of self-assembled biological structures. 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. <ref> D. Berillo et al. Formation of macroporous self-assembled hydrogels through cryogelation of Fmoc–Phe–Phe Journal of Colloid and Interface Science 368 (2012) 226–230 </ref>
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| ===Properties===
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| Therefore, we can say that SA extends the scope of chemistry aiming at [[chemical synthesis|synthesising]] products with order and functionality properties, extending chemical bonds to weak interactions and encompassing the self-assembly of NBBs on all length scales.<ref name="ozin_2005_nanochemistry">{{cite book|author=Ozin and Arsenault|title=Nanochemistry: a chemical approach to nanomaterials|publisher=Cambridge: Royal Society of Chemistry|year= 2005|isbn=0-85404-664-X}}</ref> In covalent synthesis and polymerisation, the scientist links atoms together in any desired conformation, which does not necessarily have to be the energetically most favoured position; self-assembling molecules, on the other hand, adopt a structure at the thermodynamic minimum, finding the best combination of interactions between subunits but not forming covalent bonds between them. In self-assembling structures, the scientist must predict this minimum, not merely place the atoms in the location desired.
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| Another characteristic common to nearly all self-assembled systems is their ''[[thermodynamic stability]]''. For SA 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 [[superlattice]]s 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.<ref>{{cite journal|doi=10.1021/la00048a054|title=Mechanism of formation of two-dimensional crystals from latex particles on substrates|year=1992|author=Denkov, N.|journal=Langmuir|volume=8|pages=3183|last2=Velev|first2=O.|last3=Kralchevski|first3=P.|last4=Ivanov|first4=I.|last5=Yoshimura|first5=H.|last6=Nagayama|first6=K.|issue=12}}</ref>
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| 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 SA. 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 SA, which is generally not observed in materials synthesised by other techniques: ''reversibility''.
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| From what we have written so far, it should be evident that SA is a process which is easily influenced by external parameters: if this can make synthesis more problematic due to the many free parameters that require control, on the other hand it has the exciting advantage that a large variety of shapes and functions on many length scales can be obtained.<ref name=for>{{cite journal|doi=10.1126/science.1071063|date=Mar 2002|author=Lehn, Jm|title=Toward self-organization and complex matter|volume=295|issue=5564|pages=2400–3|issn=0036-8075|pmid=11923524|journal=Science}}</ref>
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| Generally speaking, the fundamental condition needed for NBBs to self-assemble into an ordered structure is the simultaneous presence of long-range repulsive and short-range attractive forces.<ref>{{cite journal|doi=10.1002/1521-3773(20020201)41:3<457::AID-ANIE457>3.0.CO;2-W|title=Open-Framework Nickel Succinate, [Ni7(C4H4O4)6(OH)2(H2O)2]⋅2 H2O: A New Hybrid Material with Three-Dimensional Ni−O−Ni Connectivity|year=2002|author=Forster, Paul M.|journal=Angewandte Chemie International Edition|volume=41|pages=457|last2=Cheetham|first2=Anthony K.|issue=3}}</ref> Figure [fig_sa_scheme] exemplifies SA occurring from building blocks made up of two different units (A and B) which are covalently linked (short-range attraction) and repel each other by long-range interactions (e.g. because A is hydrophobic and B is hydrophilic). Since the energy of the system will unfavour configurations where A is close to B, and still no macrophase separation is possible due to A—B covalent bonds, the system will adopt a configuration where the contact area between A and B is minimised. This results in a periodic ordered structure (in figure [fig_sa_scheme] this is exemplified by a lamellar structure). For a list of repulsive-attractive competing forces which can give rise to SA phenomena.<ref name=for/>
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| By choosing [[precursor (chemistry)|precursor]]s 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 [[block copolymer|diblock copolymers]] with different block reactivities in order to selectively embed [[maghemite]] nanoparticles and generate periodic materials with potential use as [[waveguides]].<ref>Oz Gazit, Rafail Khalfin, Yachin Cohen and Rina Tannenbaum "Self-Assembled Diblock Copolymer “Nanoreactors” as “Catalysts” for Metal Nanoparticle Synthesis" Journal of Physical Chemistry C 113 (2009) 576. http://dx.doi.org/10.1021/jp807668h</ref>
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| In 2008, Advances in Colloid and Interface Science published a study in which it was concluded that every self-assembly process in reality presents a co-assembly, which makes the former term a misnomer of a kind.<ref>Vuk Uskoković – "Isn't Self-Assembly a Misnomer? Multi-Disciplinary Arguments in Favor of Co-Assembly", Advances in Colloid and Interface Science 141 (1-2) 37 - 47 (2008). {{doi|10.1016/j.cis.2008.02.004}}</ref> The thesis is built on the concept of mutual ordering of the self-assembling system and its environment.
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| == Self-assembly at the macroscopic scale ==
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| Self-assembly processes can be observed in systems of macroscopic building blocks. These building blocks can be externally propelled<ref>{{cite journal|doi=10.1162/artl.1994.1.413|title=Dynamics of self-assembling systems: Analogy with chemical kinetics|year=1994|author=Hosokawa K.|journal=Artificial Life|volume=1|pages=413–427|last2=Shimoyama|first2=I.|last3=Miura|first3=H.|issue=4}}</ref> or self-propelled.<ref>{{cite journal|doi=10.1109/TRO.2006.882919|title=Autonomous self-assembly in swarm-bots|first4=Marco|last4=Dorigo|year=2006|first3=Francesco|author=Groß R.|journal=IEEE Transactions on Robotics|last3=Mondada|volume=22|pages=1115–1130|last2=Dorigo|first2=M.|issue=6}}</ref> Since the 1950s, scientists have built self-assembly systems exhibiting centimeter-sized components ranging from passive mechanical parts to mobile robots.<ref>{{cite journal|doi=10.1109/JPROC.2008.927352|title=Self-assembly at the macroscopic scale|year=2008|author=Groß R.|journal=Proceedings of the IEEE|volume=96|pages=1490–1508|last2=Dorigo|first2=M.|issue=9}}</ref> For systems at this scale, the component design can be precisely controlled. For some systems, the components' interaction preferences are programmable. The self-assembly processes can be easily monitored and analyzed by the components themselves or by external observers.
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| == Consistent concepts of self-organization and self-assembly ==
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| [[Self-organization]] and self-assembly are regularly used 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 is developed from "dynamic small-scale interactions" according to an article in a November/December 2008 issue of Complexity.[http://www3.interscience.wiley.com/journal/121358448/abstract?CRETRY=1&SRETRY=0] Self-organization is a nonequilibrium process where self-assembly is a spontaneous process that leads toward equilibrium. 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 these initial encodings are not necessary. Another slight contrast refers to the minimum number of units needed to make an order. Self-organization appears to have a minimum number of units whereas self-assembly does not. These terms are becoming more necessary as more is learned about natural selection. Eventually, these patterns may form one theory regarding the pattern formation in nature.<ref>{{cite journal|author=Halley, J. D. and Winkler, D.A. |year=2008|title=Consistent Concepts of Self-organization and Self-assembly|doi=10.1002/cplx.20235|journal=Complexity|volume=14|pages=10|issue=2}}</ref>
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| ==See also==
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| *[[Crystal engineering]]
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| *[[Autopoiesis]]
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| *[[Langmuir–Blodgett film]]
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| *[[Nanotechnology]]
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| *[[Pick-and-place machine]]
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| *[[Self-assembly of nanoparticles]]
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| ==References==
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| {{reflist}}
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| ==External links and further reading==
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| * Book chapter "Challenges and breakthroughs in recent research on self-assembly", Sci. Technol. Adv. Mater. 9 (2007) 014109 (96 pages) ('''''[http://dx.doi.org/10.1088/1468-6996/9/1/014109 free download]''''')
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| * Kuniaki Nagayama, ''[http://www.vega.org.uk/video/programme/70 Freeview Video 'Self-Assembly: Nature's Way To Do It]'', A Royal Institution Lecture by the Vega Science Trust.
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| * Paper [http://www.esi-topics.com/msa/ Molecular Self-Assembly]
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| * Paper [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=122665 Beyond molecules: Self-assembly of mesoscopic and macroscopic components]
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| * Whitesides, G. M. & Grzybowski, B. (2002) Science 295, 2418-2421.
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| * Pablo F. Damasceno, Michael Engel & [[Sharon Glotzer]] (2012) Science 337, 453-457
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| * Rothemund PWK, Papadakis N, Winfree E (2004) [http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0020424 ''Algorithmic Self-Assembly of DNA Sierpinski Triangles'']. PLoS Biol 2(12)
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| * Wiki: ''[http://c2.com/cgi/wiki?SelfAssembly C2 Self Assembly from a computer programming perspective].''
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| * Pelesko, J.A., (2007) [http://www.pelesko.com ''Self Assembly: The Science of Things That Put Themselves Together,''] Chapman & Hall/CRC Press.
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| * A brief page on DNA self-assembly ''[http://reza.nanodetails.com ''DNA Self Assembly for Nanotechnology'']
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| * A brief page on self-assembly at the University of Delaware [http://www.math.udel.edu/MECLAB/Projects/SelfAssembly/selfassembly1.htm ''Self Assembly'']
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| * Mohammadzadegan R, Sheikhi MH (2007) ''[http://www.informaworld.com/openurl?genre=article&issn=0892-7022&volume=33&issue=13&spage=1071 ''DNA Nano-Gears] Molecular Simulation 33(13); 1071-1081.
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| * [http://www.uni-ulm.de/~hhoster/personal/self_assembly.htm Structure and Dynamics of Organic Nanostructures]
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| * [http://www.uni-ulm.de/~hhoster/personal/metal_organic.htm Metal organic coordination networks of oligopyridines and Cu on graphite]
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| {{DEFAULTSORT:Self-Assembly}}
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| <!--Categories-->
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| [[Category:Nanotechnology]]
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| [[Category:Cell biology]]
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| [[Category:Systems theory]]
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| [[Category:Self-organization]]
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| [[pl:Samoorganizacja]]
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Ed is what people contact me and my wife doesn't like it at all. My day occupation is an information officer but I've already utilized for an additional 1. She is really fond of caving but she doesn't have the time lately. Ohio is where his home is and his family loves it.
Also visit my homepage :: clairvoyants (sivuland.biz)