(282e) Flow Induced Segregation In Suspensions of Mixtures of Deformable Capsules In Confined Geometries Using the Boundary Integral Method

Flow induced segregation in mixtures of deformable particles
is relevant in many problems including the separation or detection of diseased
RBCs from their normal counterpart. These systems also serve as a model
for investigating the flow behavior of drug delivery particles in circulation.
In this work, we develop a fast O(NlogN) method for solving the Stokes flow
boundary integral equation in an arbitrary geometry. The acceleration
in the method is provided by the use of General Geometry
Ewald Like Method (GGEM) for computing the Green's function
in the geometry of interest. This algorithm is employed to
study sheared suspensions of mixtures of deformable capsules
with different rigidities in a slit geometry. Most results are
presented for suspensions with a volume fraction
of phi=0.2, with the constituent particles' capillary number being
Ca=0.2 (stiff) and Ca=0.6 (floppy). It is found that
in a suspension of primarily stiff particles, the mean wall
normal position of both the stiffer and the floppy particle
are comparable. With increasing concentrations of the floppy
particle, the mean position of the stiffer particle shifts
towards the wall. The particle concentration distribution
along the channel height reveals that the stiffer particles
tend to form a layered structure as evidenced by the presence
of distinct peaks; the strength of the peaks closer to the wall
increases with increasing concentration of the floppy particle.
In contrast, the floppy particles exhibit a near singly peaked
distribution around the centerline with  weak signs of layering.
A mechanistic theory is developed to explain the flow induced
segregation in mixtures of deformable particles under confinement.