(39d) Microfluidic Strategies to Mix Highly Viscous and/or Non-Newtonian Fluids

The decreases
in volume and improvements in system control afforded by microfluidics have
been taken advantage of by researchers in fields ranging from cell biology to
catalysis with the idea of a complete ?lab on a chip? becoming a realistic goal. 
However, the application of microfluidics has been limited in cases where the
fluids involved are highly viscous, are of significantly different viscosities
and/or are non-Newtonian in nature.  This is especially true of strategies for
mixing highly viscous fluids on the microscale.

Functionally,
the rate of fluid flow in a microfluidic device can be affected by the applied
pressure, the device geometry, the viscosity of the fluid, and the time for
flow.  Thus, in order to successfully maintain flow in a microfluidic
environment with increasingly viscous fluids there are a limited number of
parameters which must be considered during the device design.  We discuss here
these design rules and apply them to drive fluid flow in a microfluidic mixer
capable of mixing fluids at the 20 nL level [1].  The viscosities of the
solutions to be mixed here differ by a factor of ~30; 2.45×10^-2 Pa-s
for a monoolein lipid phase (1-monooleoyl-rac-glycerol, Fluka), versus
7.98×10^-4 Pa-s for an aqueous phase.  Furthermore, the resulting
mixture has a viscosity that is a factor of ~10⁵ larger (~48.3 Pa-s
at a shear rate of 71.4 s^-1) than the viscosity of the aqueous phase
and exhibits non-Newtonian behavior [2].

References:

[1]  Perry, S. L.; Roberts, G. W.; Tice,
J. D.; Gennis, R. B.; Kenis, P. J. A., Cryst Growth Des 2009 (in
press, DOI: 10.1021/cg900289d).

[2]  Bonacucina, G.; Palmieri, G. F.;
Craig, D. Q. M., Journal of Pharmaceutical Sciences 2005, 94,
2452-2462.