Particle manipulation with oscillatory non-linear microfluidics

In this work, inertial and electro-inertial nonlinear phenomena arising in oscillatory microfluidic flows in the 10 - 1000 Hz range and their potential for manipulating microparticles are experimentally examined and supported with theory and simulation. First, the use of viscous streaming flows, which are steady secondary vortices emerging due to inertia near a solid surface immersed in an oscillatory background flow are considered. For a particular surface geometry, the viscous streaming vortices are shown to manifest in qualitatively distinct topological phases depending on the frequency. These phases are characterized by the configuration of centers and saddle points of the vortices. It is shown that particles can either be ‘attracted’ and trapped or ‘repelled’ and cleared away from the flow path around the boundary by choosing the geometry appropriately. The particle manipulation efficiency is found to improve with an increasing frequency above a minimum threshold below which particle manipulation is ineffective. Next, the cross-streamline inertial migration of particles in a quasi-2D channel flow to specific stable positions, known as inertial focusing, is examined in 10 - 1000 Hz oscillatory flows. It is found that oscillatory flows enable the focusing of much smaller particles than possible with conventional steady flow inertial focusing due to the large effective length (1 - 10 m) traveled by particles even in a relatively short channel (4 cm). In this case, there exists a critical frequency above which focusing efficiency decreases rapidly but below which it is constant, in contrast with steady streaming. Further, the oscillatory flows enable precise measurement of the migration velocities which can be directly compared against analytical theories and numeric simulations. A corresponding asymptotic theory is also derived and its prediction is compared against migration velocity and focusing position measurements to good concord. Finally, the Brownian limitation on inertial focusing is surpassed using cross-coupled nonlinear interaction between synchronized oscillatory hydrodynamic and electrokinetic effects, a technique referred to as Synchronized Oscillatory Electro-Inertial Focusing (SOEIF). SOEIF is demonstrated to be capable of manipulating particles up to 3 orders of magnitude smaller than the channel width (corresponding to Re_p<<0.001). The phase difference between the oscillatory flow and field is found to be a critical parameter and its effect is characterized by measurements of focusing position, efficiency, and migration velocities. It is found that the focusing position can be tuned to anywhere between the channel center and the wall by changing the phase difference between the field and flow. Additional measurements towards uncovering the precise mechanism of SOEIF are also presented.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Vishwanathan, Giridar

Contributors dc:contributor

• Juarez, Gabriel
• Smith, Kyle
• Chen, Qian
• Hilgenfeldt, Sascha

• Oscillatory microfluidics
• Nonlinear microfluidics
• Inertial microfluidics
• Electrophoresis
• Particle manipulation
• Acoustic streaming
• Electrokinetics

Statement dc:rights

• Copyright 2022 Giridar Vishwanathan

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115909

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115909