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SUMMARY:Does shear induced demixing resemble a thermodynamically driven in
 stability? - Joseph Peterson\, DAMTP
DTSTART:20190129T130000Z
DTEND:20190129T140000Z
UID:TALK116908@talks.cam.ac.uk
CONTACT:Etienne Fodor
DESCRIPTION:In most theoretical and experimental studies of multi-componen
 t complex fluids\, it is implicitly assumed that if a fluid is well-mixed 
 at rest\, it will remain well mixed in flow.  To leading order\, this may 
 be a reasonable first approximation for many materials and many applicatio
 ns.  However\, there is an abundance of experimental evidence to show that
  well-mixed polymer melts and solutions can fractionate or even demix in t
 he presence of a sufficiently strong shear flow.  These phenomena are scie
 ntifically interesting but also industrially pertinent\; millions of pound
 s of polymers are processed every day\, and unexpected compositional inhom
 ogeneity can negatively impact operating conditions and/or product quality
 .\n\nTheoretical studies on compositionally inhomogeneous flows of polymer
  melts and solutions have typically made use of two-fluid models\, wherein
  the molecular details of each species are coarse-grained into a set of su
 perimposable continuum fluids.  The relative motions of the two fluids are
  restricted by frictional drag\, and the collective motions of the two flu
 ids are restricted by incompressibility of the overall velocity field.  In
  the present talk\, we employ a two-fluid model of semi-dilute entangled p
 olymer solutions to consider whether the linear and nonlinear dynamics of 
 a shear induced demixing instability.  We will present a summary of result
 s for linear stability\, nonlinear evolution\, and provide a visual compar
 ison to the results of a thermodynamically driven model of demixing.  Fina
 lly\, we make use of an asymptotically limiting version of the model to de
 termine whether shear induced demixing resembles a thermodynamically drive
 n demixing instability\, as has often been assumed.  We will show that\, s
 urprisingly\, the answer to this question depends on the nature of the imp
 osed deformation (e.g. steady vs. unsteady flow).
LOCATION:MR11\, CMS
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