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Study of microfluidic measurement techniques using novel optical imaging diagnostics
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Novel microscale velocity and temperature measurement techniques were studied based on confocal laser scanning microscopy (CLSM) and optical serial sectioning microscopy (OSSM). Two microscopic measurement systems were developed, 1) a CLSM micro particle image velocimetry (PIV) system with a dual Nipkow disk confocal unit (CSU-10), a CW argon-ion laser and an upright microscope, and 2) an OSSM micro- particle tracking velocimetry (PTV) system with an epi-fluorescence microscope and a non-designed specimen to make a three-dimensional (3-D) diffraction particle image. The CLSM micro-PIV system shows a unique optical slicing capability allowing true depth-wise resolved vector field mapping. A comparative study is presented between the CLSM micro-PIV and a conventional epi-fluorescence micro-PIV. Both have been applied to the creeping Poiseuille flows in two different microtubes of 99-ÃÂµm (Re = 0.00275) and 516-ÃÂµm ID diameters (Re = 0.021). The CLSM micro-PIV consistently shows significantly improved particle image contrasts, the definition of "optical slicing" and measured flow vector fields more accurately agreeing with predictions based on the Poiseuille flow fields, compared to the conventional micro-PIV. The OSSM micro-PTV technique is applied for a 3-D vector field mapping in a microscopic flow and a Brownian motion tracking of nanoparticles. This technique modifies OSSM system for a micro-fluidic experiment, and the imaging system captures a diffracted particle image having numerous circular fringes instead of an in-focus particle image. The 3-D particle tracking is based on a correlation between the 3-D diffraction pattern of a particle and the defocus distance from a focal plane. A computational program is invented for the OSSM micro-PTV, and provides a 3-D velocity vector field with a spatial resolution of 5.16 ÃÂµm. In addition, a concept of nonintrusive thermometry is presented based on the correlation of the Brownian motion of suspended nanoparticles with the surrounding fluid temperature. Detection of fully three-dimensional Brownian motion is possible by the use of the OSSM, and the measured value of mean square displacement (MSD) is compared fairly well with Einstein's predictions.
Park, Jaesung (2005). Study of microfluidic measurement techniques using novel optical imaging diagnostics. Doctoral dissertation, Texas A&M University. Texas A&M University. Available electronically from