The effects of polymer molecular weight on filament thinning<br/><br/>& drop breakup in microchannels

Tuesday, October 13, 2009 - 9:00am - 9:40am
EE/CS 3-180
Paulo Arratia (University of Pennsylvania)
In this talk, the effects of fluid elasticity on the dynamics
of filament thinning and drop breakup processes are
investigated in a cross-slot microchannel. Elasticity effects
are examined using dilute aqueous polymeric solutions of
molecular weight (MW) ranging from 1.5 x 10(^3) to 1.8 ×
10(^7). Results for polymeric fluids are compared to those for
a viscous Newtonian fluid. The shearing or continuous phase
that induces breakup is mineral oil. All fluids possess similar
shear-viscosity (~0.2 Pa s) so that the viscosity ratio between
the oil and aqueous phases is close to unity. Measurements of
filament thickness as a function of time show different
thinning behavior for the different aqueous fluids. For
Newtonian fluids, the thinning process shows a single
exponential decay of the filament thickness. For low MW fluids
(103, 104, and 105), the thinning process also shows a single
exponential decay, but with a decay rate that is slower than
for the Newtonian fluid. The decay time increases with polymer
MW. For high MW (106 and 107) fluids, the initial
exponential decay crosses over to a second exponential decay in which
elastic stresses are important. We show that the decay rate of
the filament thickness in this exponential decay regime can be
used to measure the steady extensional viscosity of the fluids.
At late times, all fluids cross over to an algebraic decay
which is driven mainly by surface tension.
MSC Code: