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SUMMARY:Contr. Talk 7 - Spherical Harmonics Expansion show Chain Retractio
 n
DTSTART;VALUE=DATE-TIME:20181211T090000Z
DTEND;VALUE=DATE-TIME:20181211T092000Z
DTSTAMP;VALUE=DATE-TIME:20260523T152609Z
UID:indico-contribution-486@lindico453.srv.lu.se
DESCRIPTION:Speakers: Anine Borger (Niels Bohr Institute\, University of C
 openhagen)\nThe mechanical properties of polymer melts under deformation a
 re well described by the tube model developed in the 1970s by de Gennes an
 d Doi and Edwards. In the model\, the restricted motion of a chain due to 
 its neighbors is modeled as if the chain ia confined to a tube. However\, 
 the validity of the tube model for rapid deformations compared to the mole
 cular relaxation was recently questioned [1]. They proposed a new analysis
  method for anisotropic 2D small angle (neutron) scattering\, SANS\, data 
 for uniaxially extended polymer melts expanding the data in spherical harm
 onics to ease the separation of the isotropic and anisotropic contribution
 s. Using this method\, they looked for the signature of chain retraction\,
  see below\, during relaxation after deformation which is a cornerstone of
  the tube model. The signature was absent in their data which lead them to
  conclude that chain retraction either does not occur or that it is shield
 ed by some other non-linear effect not yet included in the model. However\
 , we employ the same analysis also on SANS data for a polystyrene melt of 
 about a factor of five lower molar mass stretched more than a factor of te
 n more\, and we do see the proposed signature in the harmonics: The minimu
 m in the expansion coefficient of the leading anisotropic contribution to 
 the scattering pattern shifts towards larger q as the relaxation times app
 roaches the Rouse time\, τR. We therefore conclude that the relaxation of
  the molecular stretching and orientation are decoupled\, or in other word
 s that the chain retracts\, which supports the tube model.\nChain retracti
 on arises during relaxation if the deformation is fast enough to not only 
 orient the chains but also stretch them. The hypothesis of the tube model 
 is that the relaxation of the stretching of the molecule happens on a fast
  time scale\, τR\, through a Rouse-like process whereas the relaxation of
  the orientation happens on a much slower timescale through repetition. Th
 at these timescales are well separated causes the molecule to shrink in al
 l dimensions for t∼τR does it relax back to its equilibrium shape.\n\nh
 ttps://lindico453.srv.lu.se/event/67/contributions/486/
LOCATION:Elite Hotel Ideon Tera
URL:https://lindico453.srv.lu.se/event/67/contributions/486/
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