Generation Of Sub-Wavelength Acoustic Stationary Waves In Microfluidic Platforms: Theory And Applications To The Control Of Micro-Nanoparticles And Biological Entities.

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Presented in this dissertation are the theoretical modeling and experimental results of a novel method for manipulating micro and nanoparticles in an acoustically actuated microfluidic glass capillary. Here, the PZT (Lead Zirconate Titanate)glass capillary actuator mechanism performs bioanalytical methods such as collection, separation and mixing at microscale, at low voltage drives, enabling production of battery operated inexpensive portable microfluidic systems. Analytical and finite element modeling of the vibrational modes of the fluid filled thick walled cylindrical capillary has been also studied. Torsional, longitudinal and flexural modes and their dispersion relationships are presented. Through the excitation of the various vibrational modes of the silica capillary, sub-wavelength acoustic pressure modes in the microfluidic cavity are formed. More than 20 such sub-harmonic modes are generated harmonically in the 20kHz2MHz regime whereas naturally occurring radial modes have a cut off frequency around 9 MHz. The amplitude of these stationary acoustic pressure fields are high enough to generate nonlinear acoustic forces and streaming effects for micro and nanoparticle manipulation. Theoretical models explaining the generation of the sub-wavelength modes and acoustic radiation forces are developed. Generation of an effective macroscopic electric field as a result of the collection of charged colloidal particles under acoustic forces has been observed. This self generated field causes fast collective diffusion of nanoparticles and can counterbalance the acoustic radiation forces, so a method for calibrating acoustic force field with respect to the collective electrostatic repulsion and the Zeta potential of particles is introduced. A silicon bulk microfabricated actuator enabling different bioanalytical capabilities such as collection, separation and mixing of analytes on a single bulk-PZTsilicon microfluidic platform at low voltage drives is also demonstrated. Presented experimental results include: collection of micro and nanoparticles, colloidal systems and biological entities such as bacteria and cells; separation of micro and nanoparticles with respect to acoustic contrast factor; planar chipscale centrifugation of blood; separation of microparticles with respect to size; and controlled oscillating bubble dynamics at the microscale, which are all obtained in the PZT-glass capillary actuator driven with a typical function generator at around 100 milliwatts of power consumption.

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