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Electrokinetic Flow in Microfluidic

Devices

Mentor: Gaurav Soni

Faculty Advisor: Carl Meinhart (Mechanical Engineering)

Presenters: Sara Pham, Karina Almaraz,

Stephen Russ, and Andres Hofmann


Why Microfluidics

• Study of microfluidics is fairly new.

– Flow of fluids at macro level.

– Flow of fluids at micro level.

• “There is plenty of room at the bottom.” - Feynman

• Using a passive method with a force field like a

magnetic or a weak AC electric field is preferable.

• Further development of future biological

applications:

– Separating, concentration, mixing and pumping.


Laboratory Objectives

• To replicate the experiment and confirm results based

on previous tests.

• Obtain knowledge on what drives the flow of fluids on

the microscale.

• Measure and observe the velocity of fluids.

• To develop a new theory for the flow of fluids on the

micro level for an in depth level understanding.


Fabrication of Microfluidic Device

1.

Glass Wafer

2.

Spin Photoresist (PR)

3.

Photomask Exposure

4.

Development

5.

Metal Deposition

6.

Lift-off


Induced Charge Electro-osmosis (ICEO)

+

-

+

-

+

+

-

-

+

+

-

++++++++ ---------+++++++++ --------

Charges Change

~

Alternating Current

9 volts

163 Hz

Charges Change


Induced Charge Electro-osmosis (ICEO)

- -

++++++++

+ + + + + + - - - - - -

---------+++++++++

+ +

--------

Charges Change

Induced Charge

Charges Change

L

~

Alternating Current

9 volts

163 Hz


Induced Charge Electro-osmosis (ICEO)

+ -

+

- -

+ + + + - - - -

+ +

++++++++ ---------+++++++++

--------

Charges Change

Induced Charge

Charges Change

~

Alternating Current

9 volts

163 Hz


Fluorescence Microscope

1. Ionic solution deposited

on ICEO device

2. ICEO device placed

under microscope

3. AC power creates flows

4. Green light strikes

particles

5. Particles emit red light

6. CCD camera captures

red light

7. Computer processes

images to determine

velocity

C. Meinhart


Experimental Data Acquisition

1 mm

200 μm

Gate Electrode

10 mm

Driving

Electrode

~

AC 9V pp 163 Hz

1 mM KCl Solution with Fluorescent Particles

Driving

Electrode


Micro Particle Image Velocimetry (μPIV) Software

Image 1024x512

32x32 pixels

Image

Correlation

=

Time 1 Time 2

Displacement


T. Squires, C. Meinhart, G. Soni

Calculated Velocity of Flow

(Top View of Gate Electrode)

X-velocity (μm/s)

12

9

6

3

0

-3

-6

-9

-12

-100 -75 -50 -25 0 25 50 75 100

X (μm)

Maximum velocity was found to be approximately

12 micrometers (μm) per second (at 9 volts).


Achievements

• Studied the physics of Induced Charge

Electro-osmosis (ICEO)

• Demonstrated the existence of ICEO

using a microfluidic device

• Measured flow velocities using

Micro Particle Image Velocimetry


Thank you!

• Our mentor, Gaurav Soni!

• Faculty advisor, Carl Meinhart.

• All who supported and encouraged us.

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