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CATEGORIES:DAMTP Statistical Physics and Soft Matter Seminar
SUMMARY:Does shear induced demixing resemble a thermodynam
 ically driven instability? - Joseph Peterson\, DAM
 TP
DTSTART;TZID=Europe/London:20190129T130000
DTEND;TZID=Europe/London:20190129T140000
UID:TALK116908AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/116908
DESCRIPTION:In most theoretical and experimental studies of mu
 lti-component complex fluids\, it is implicitly as
 sumed that if a fluid is well-mixed at rest\, it w
 ill remain well mixed in flow.  To leading order\,
  this may be a reasonable first approximation for 
 many materials and many applications.  However\, t
 here is an abundance of experimental evidence to s
 how that well-mixed polymer melts and solutions ca
 n fractionate or even demix in the presence of a s
 ufficiently strong shear flow.  These phenomena ar
 e scientifically interesting but also industrially
  pertinent\; millions of pounds of polymers are pr
 ocessed every day\, and unexpected compositional i
 nhomogeneity can negatively impact operating condi
 tions and/or product quality.\n\nTheoretical studi
 es on compositionally inhomogeneous flows of polym
 er melts and solutions have typically made use of 
 two-fluid models\, wherein the molecular details o
 f each species are coarse-grained into a set of su
 perimposable continuum fluids.  The relative motio
 ns of the two fluids are restricted by frictional 
 drag\, and the collective motions of the two fluid
 s are restricted by incompressibility of the overa
 ll velocity field.  In the present talk\, we emplo
 y a two-fluid model of semi-dilute entangled polym
 er solutions to consider whether the linear and no
 nlinear dynamics of a shear induced demixing insta
 bility.  We will present a summary of results for 
 linear stability\, nonlinear evolution\, and provi
 de a visual comparison to the results of a thermod
 ynamically driven model of demixing.  Finally\, we
  make use of an asymptotically limiting version of
  the model to determine whether shear induced demi
 xing resembles a thermodynamically driven demixing
  instability\, as has often been assumed.  We will
  show that\, surprisingly\, the answer to this que
 stion depends on the nature of the imposed deforma
 tion (e.g. steady vs. unsteady flow).
LOCATION:MR11\, CMS
CONTACT:Etienne Fodor
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