Microstructure Modeling of Polymer Blends
in Complex Flows
Fredrick R. Phelan Jr.
Multiphase Material Group, Polymer Division, NIST
Tuesday, December 18, 2001 15:00-16:00,
Room 145, NIST North (820)
Gaithersburg
Tuesday, December 18, 2001 13:00-14:00,
Room 4511
Boulder
Abstract:
Polymer blends are mixtures of two or more polymers that are usually processed
in a phase-separated state in which droplets are suspended in a matrix phase.
The fluid mechanical deformation experienced by the mixture during the
processing causes the drops to deform, breakup and/or coalesce, which alters
the local size, shape and orientation of the microstructure. Since the
structural properties of the blend are in large part determined by the
structure of the droplet-phase, there is great incentive to modle the
evolution of teh blend morphology during processing. Modeling of polymer
blends in complex flows such as injection molding is highly complicated
by the fact that that the non-homogeneous deformation inherent to such flows
leads to large spatial gradients in microstructure. Since drop densities
may be as high as 1.E11 drops per cubic centimeter,
modeling of such flows using rigorous
multi-phase methods is untenable, as no single unit cell structure can be
used to represent the entire medium. For this reason, we are investigating
a multi-scale modeling approach for such flows. Volume averaged methods which
compute the average microstructure within a meso-volume that is larger than
the length scale of the mixture, but much smaller than overall volume are
used to predict overall average flow characteristics. Rigorous two-phase
simulations using diffuse interface methods are being used to model the
details of flow at the drop level. Combining these two approaches, we hope
to satisfy the need for both gross information such as pressure drop important
to a process engineer designing tooling, and detailing information on
microstructure important to materials engineer interested in properties.
Contact: A. J. KearsleyNote: Visitors from outside NIST must contact
Robin Bickel; (301) 975-3668;
at least 24 hours in advance.
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