Editing Copolymer (section)

==Microphase separation==<!-- [[Microphase separation]] redirects here -->

[[File:Sbs block copolymer.jpg|thumb|right|SBS block copolymer in [[Transmission electron microscopy|TEM]]]]

Block copolymers can "microphase separate" to form periodic [[nanostructures]],<ref>Hamley, I.W. "The Physics of Block Copolymers" – Oxford University Press, 1998.</ref><ref>Hamley, I.W. "Developments in Block Copolymer Science and Technology" – Wiley, 2004.</ref> such as styrene-butadiene-styrene block copolymer. The polymer is known as [[Kraton (polymer)|Kraton]] and is used for shoe soles and [[adhesive]]s. Owing to the microfine structure, transmission electron microscope or [[Transmission electron microscopy|TEM]] was used to examine the structure. The butadiene matrix was stained with [[osmium tetroxide]] to provide contrast in the image. The material was made by [[living polymerization]] so that the blocks are almost [[monodisperse]] to create a regular microstructure. The [[molecular weight]] of the polystyrene blocks in the main picture is 102,000; the inset picture has a molecular weight of 91,000, producing slightly smaller domains.

[[Image:SBSstructure.svg|thumb|right|SBS block copolymer schematic microstructure]]

Microphase separation is a situation similar to that of [[oil]] and [[water]]. Oil and water are immiscible (i.e., they can phase separate). Due to the incompatibility between the blocks, block copolymers undergo a similar phase separation. Since the blocks are covalently bonded to each other, they cannot demix macroscopically like water and oil. In "microphase separation," the blocks form [[nanometer]]-sized structures. Depending on the relative lengths of each block, several morphologies can be obtained. In diblock copolymers, sufficiently different block lengths lead to nanometer-sized spheres of one block in a matrix of the second (e.g., [[Polymethyl methacrylate|PMMA]] in polystyrene). Using less different block lengths, a "hexagonally packed cylinder" geometry can be obtained. Blocks of similar length form layers (often called [[lamella (materials)|lamellae]] in the technical literature). Between the cylindrical and lamellar phase is the [[gyroid]] phase. The nanoscale structures created from block copolymers can potentially be used to create devices for computer [[memory]], nanoscale-templating, and nanoscale separations.<ref>{{cite journal | last1 = Gazit | first1 = Oz | last2 = Khalfin | first2 = Rafail | last3 = Cohen | first3 = Yachin | last4 = Tannenbaum | first4 = Rina | author4-link = Rina Tannenbaum | year = 2009 | title = Self-assembled diblock copolymer "nanoreactors" as catalysts for metal nanoparticle synthesis | journal = Journal of Physical Chemistry C | volume = 113 | issue = 2| pages = 576–583 | doi = 10.1021/jp807668h }}</ref> Block copolymers are sometimes used as a replacement for phospholipids in [[model lipid bilayer]]s and [[liposome]]s for their superior stability and tunability.<ref>{{cite journal | last1=Meier | first1=Wolfgang | last2=Nardin | first2=Corinne | last3=Winterhalter | first3=Mathias | title=Reconstitution of Channel Proteins in (Polymerized) ABA Triblock Copolymer Membranes | journal=Angewandte Chemie International Edition | publisher=Wiley | volume=39 | issue=24 | date=2000-12-15 | issn=1433-7851 | doi=10.1002/1521-3773(20001215)39:24<4599::aid-anie4599>3.0.co;2-y | pages=4599–4602| pmid=11169683 }}</ref><ref>{{cite journal | last1=Zhang | first1=Xiaoyan | last2=Tanner | first2=Pascal | last3=Graff | first3=Alexandra | last4=Palivan | first4=Cornelia G. | last5=Meier | first5=Wolfgang | title=Mimicking the cell membrane with block copolymer membranes | journal=Journal of Polymer Science Part A: Polymer Chemistry | publisher=Wiley | volume=50 | issue=12 | date=2012-03-11 | issn=0887-624X | doi=10.1002/pola.26000 | pages=2293–2318| bibcode=2012JPoSA..50.2293Z | doi-access=free }}</ref>

Polymer scientists use [[thermodynamics]] to describe how the different blocks interact.<ref>{{cite journal|author-link1=Frank S. Bates |author-link2=Glenn H. Fredrickson | last1 = Bates | first1 = Frank S.  | last2 = Fredrickson | first2 = Glenn H. | year = 2014 | title = Block Copolymer Thermodynamics: Theory and Experiment | journal = Annual Review of Physical Chemistry | volume = 41 | pages = 525–557 | doi = 10.1146/annurev.pc.41.100190.002521| bibcode = 1990ARPC...41..525B | pmid = 20462355}}</ref><ref>{{cite journal | last1 = Chremos | first1 = Alexandros | last2 = Nikoubashman | first2 = Arash | last3 = Panagiotopoulos | first3 = Athanassios | year = 2014 | title = Flory-Huggins parameter χ, from binary mixtures of Lennard-Jones particles to block copolymer melts | journal = J. Chem. Phys. | volume = 140 | issue = 5| pages = 054909 | doi = 10.1063/1.4863331 | pmid = 24511981 | bibcode = 2014JChPh.140e4909C }}</ref> The product of the degree of polymerization, ''n'', and the Flory-Huggins [[interaction parameter]], <math>\chi</math>, gives an indication of how incompatible the two blocks are and whether they will microphase separate. For example, a diblock copolymer of symmetric composition will microphase separate if the product <math>\chi N</math> is greater than 10.5. If <math>\chi N</math> is less than 10.5, the blocks will mix and microphase separation is not observed. The incompatibility between the blocks also affects the solution behavior of these copolymers and their adsorption behavior on various surfaces.<ref>{{cite journal | last1 = Hershkovitz | first1 = Eli | last2 = Tannenbaum | first2 = Allen | author2-link = Allen Tannenbaum | last3 = Tannenbaum | first3 = Rina | author3-link = Rina Tannenbaum | year = 2008 | title = Adsorption of block co-polymers from selective solvents on curved surfaces | journal = Macromolecules | volume = 41 | issue = 9| pages = 3190–3198 | doi = 10.1021/ma702706p | pmid = 20976029 | bibcode = 2008MaMol..41.3190H | pmc=2957843}}</ref>

Block copolymers are able to self-assemble in selective solvents to form micelles among other structures.<ref>Hamley, I.W. "Block Copolymers in Solution" – Wiley, 2005.</ref>

In thin films, block copolymers are of great interest as masks in the lithographic patterning of semiconductor materials for applications in high density data storage. A key challenge is to minimise the feature size and much research is in progress on this.<ref>{{cite journal | last1 = Hamley | first1 = IW | year = 2009 | title = Ordering in Thin Films of Block Copolymers: Fundamentals to Potential Applications | journal = Progress in Polymer Science | volume = 34 | issue = 11| pages = 1161–1210 | doi = 10.1016/j.progpolymsci.2009.06.003 }}</ref>