Editing Polymer physics (section)

==Flexibility and reptation==
Whether a polymer is flexible or not depends on the scale of interest.  For example, the [[persistence length]] of double-stranded [[DNA]] is about 50&nbsp;nm. Looking at length scale smaller than 50&nbsp;nm, it behaves more or less like a rigid rod.<ref>G.McGuinness, ''Polymer Physics'', Oxford University Press, p347</ref> At length scale much larger than 50&nbsp;nm, it behaves like a flexible chain.

[[Reptation]] is the thermal motion of very long linear, ''entangled'' basically
[[macromolecules]] in [[polymer]] melts or concentrated polymer solutions. Derived from the word [[reptile]], reptation suggests the movement of entangled polymer chains as being analogous to [[snake]]s slithering through one another.<ref name="Rubinstein">{{cite conference | url=http://www.aps.org/units/dpoly/resources/degennes.cfm | title=Dynamics of Entangled Polymers | publisher=American Physical Society | access-date=6 April 2015 | author=Rubinstein, Michael |date=March 2008  | conference=Pierre-Gilles de Gennes Symposium | location=New Orleans, LA}}</ref> [[Pierre-Gilles de Gennes]] introduced (and named) the concept of reptation into polymer physics in 1971 to explain the dependence of the mobility of a macromolecule on its length. Reptation is used as a mechanism to explain viscous flow in an amorphous polymer.<ref>{{Cite journal | last1 = De Gennes | first1 = P. G. | title = Entangled polymers | doi = 10.1063/1.2915700 | journal = Physics Today | publisher = American Institute of Physics | volume = 36 | issue = 6 | pages = 33–39 | year = 1983 | quote = A theory based on the snake-like motion by which chains of  monomers move in the melt is enhancing our understanding of rheology, diffusion, polymer-polymer  welding, chemical kinetics and  biotechnology|bibcode = 1983PhT....36f..33D }}</ref><ref>{{Cite journal | last1 = De Gennes | first1 = P. G. | title = Reptation of a Polymer Chain in the Presence of Fixed Obstacles | doi = 10.1063/1.1675789 | journal = The Journal of Chemical Physics | publisher = American Institute of Physics | volume = 55 | issue = 2 | pages = 572–579 | year = 1971 |bibcode = 1971JChPh..55..572D }}</ref>  [[Sam Edwards (physicist)|Sir Sam Edwards]] and [[Masao Doi]] later refined reptation theory.<ref>{{citation |title=Samuel Edwards: Boltzmann Medallist 1995 |publisher=IUPAP Commission on Statistical Physics |url=http://iupap.cii.fc.ul.pt/Boltz_Award/BA1995.html |access-date=2013-02-20 |url-status=dead |archive-url=https://web.archive.org/web/20131017061732/http://iupap.cii.fc.ul.pt/Boltz_Award/BA1995.html |archive-date=2013-10-17 }}</ref><ref name="flow">{{Cite journal | last1 = Doi | first1 = M. | last2 = Edwards | first2 = S. F. | doi = 10.1039/f29787401789 | title = Dynamics of concentrated polymer systems. Part 1.?Brownian motion in the equilibrium state | journal = Journal of the Chemical Society, Faraday Transactions 2 | volume = 74 | pages = 1789–1801 | year = 1978 }}</ref> The consistent theory of thermal motion of polymers was given by [[Vladimir Pokrovskii]]<ref>{{Cite journal | last1 = Pokrovskii | first1 = V. N. | doi = 10.1016/j.physa.2005.10.028 | title = A justification of the reptation-tube dynamics of a linear macromolecule in the mesoscopic approach | journal = Physica A: Statistical Mechanics and Its Applications | volume = 366 | pages = 88–106| year = 2006 |bibcode = 2006PhyA..366...88P }}</ref> 
.<ref>{{Cite journal | last1 = Pokrovskii | first1 = V. N. | title = Reptation and diffusive modes of motion of linear macromolecules | doi = 10.1134/S1063776108030205 | journal = Journal of Experimental and Theoretical Physics | volume = 106 | issue = 3 | pages = 604–607 | year = 2008 | bibcode = 2008JETP..106..604P | s2cid = 121054836 }}</ref><ref>{{Cite book|title=The Mesoscopic Theory of Polymer Dynamics, the second edition.|last=Pokrovskii|first=Vladimir|series=Springer Series in Chemical Physics |publisher=Springer, Dordrecht-Heidelberg-London-New York.|year=2010|volume=95 |isbn=978-90-481-2230-1|url=https://link.springer.com/book/10.1007%2F978-90-481-2231-8|pages=|doi=10.1007/978-90-481-2231-8 }}</ref>  Similar phenomena also occur in proteins.<ref>{{Cite journal
 | pmid = 11575938
| year = 2001
| last1 = Bu
| first1 = Z
| title = Dynamic regimes and correlated structural dynamics in native and denatured alpha-lactalbumin
| journal = Journal of Molecular Biology
| volume = 312
| issue = 4
| pages = 865–73
| last2 = Cook
| first2 = J
| last3 = Callaway
| first3 = D. J.
| doi = 10.1006/jmbi.2001.5006
| s2cid = 23418562
}}</ref>