Interplay between orientation and lift forces on non-spherical particles in complex fluids

Purdue University, West Lafayette IN

Investigators

Abstract

Viscoelastic suspensions are polymeric fluids containing particles. These systems are everywhere in our daily lives, for example, found in foods, consumer products, coatings, adhesives, and pastes (e.g., 3D printing). These systems are also common in biological fluids (e.g., mucous, blood, bacterial suspensions). One interesting feature of viscoelastic suspensions is that particles in such fluids acquire lift forces during pressure-driven flows that drive them toward specific regions in the fluid. This phenomenon is important in polymer processing because it determines the final structure of the materials. It is also important in microfluidic technologies where flow is used to separate biological suspensions by particle size and shape. While the lift forces are well-studied for spherical particles, little is known about how particle shape affects the lift because the phenomenon is highly coupled to the particle orientation, which itself is a function of the flow. This award will perform experiments, simulations, and theories to characterize the motion of non-spherical particles in polymeric fluids and quantify the coupling between the lift and orientation for different flow rates, particle geometries, fluid properties, and channel confinement. This information is valuable for processing rod-like and disk-like particles in viscoelastic suspensions in the applications mentioned above, as it provides design guidelines for the migration time and final location for different particle shapes. This study specifically will perform microfluidic experiments where one flows a dilute suspension of spheroids (prolate and oblate) through a tube. Different fluids and channel sizes will be used, allowing one to systematically vary the fluid properties and channel confinement. The particle’s 3D position and orientation distribution at different channel locations will be visualized using holography, allowing one to obtain long-time particle positions and rate of migration. Direct numerical simulations and theories will complement the studies, developing relationships for lift forces in this geometry as well as other geometries that are important for fluid characterization. Both investigators will create demos about complex fluids for Purdue’s Women in Engineering Program, as well as create similar exhibits for elementary school students at Imagination Station, a local science center. These exhibits will be run by undergraduates working in the respective labs and an honors engineering society advised by the investigators. Lastly, undergraduates from underrepresented communities will be recruited for research through Purdue’s SURF program. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.