טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMiezner Meiran
SubjectParametric Study of Double Emulsion Droplet Generation in
a Microfluidic Device
DepartmentDepartment of Aerospace Engineering
Supervisor Dr. Ian Jacobi


Abstract

Commercial fluorescent tracer particles used for particle image velocimetry (PIV) in fluid mechanics and particle dispersion experiments, are available in a very limited range of densities, and are prohibitively expensive for largescale experiments. Therefore, a method for producing tracer particles with a wide range of densities, in a robust and inexpensive way is highly desirable.

In this study, we extend an earlier microfluidic system of double emulsion droplets generation in a co-flow microcapillary device, using salt-water solution to control droplet density.

We analyzed the sources of polydispersity in size of the droplets in our primary system, to compare it with commercial particles. We found the flow driven system we used was a source of fluctuation in the flow, resulting in high polydispersity in particles size. We improved our droplet production by building a pressure-driven operation that reduces polydispersity of the droplet’s size and thus reduces polydispersity of its density as well.


Measuring droplets size to get polydispersity is challenging, since the production rate is extremely high. Therefore, we had to automate the measuring process by writing an image analysis code, which iterates over thousands of images for every run in the experiment, detecting and measuring the inner and outer layer of all the droplets in the focus plane.


To obtain fluorescent droplets, the outer layer of the droplets was dyed. Using a commercial liquid dye resulted in a very low fluorescence intensity with respect to the intensity obtained from commercial particles.

Replacing the commercial liquid dye with Nile-Red, when used in  low concentration in the outer layer of the particle, was found to produce higher fluorescence intensity than the intensity of particles dyed with the maximum concentration of the liquid dye, and also results in higher intensity than that of the commercial particles.


We optimize the fluorescence and polydispersity of the resulting particles as a function of chemistry and flow properties and examined the robustness and operating limits of the new system. Finally, we validated the sufficiency of the fluorescent response of the fabricated particles in a realistic experimental environment.