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Electrokinetic Flows in
Microfluidic Devices
Mentor: Gaurav Soni
Principle Researcher: Carl Meinhart
Department of Mechanical Engineering
SIMS Students:
Alesia Clemente, Peter Salazar, Scott Strutner, Trevor Wolfcale

Introduction
Electrokinetics: The study of fluid flow under the
influence of electric fields.
• Medical
• Rapid testing for Biological agents
• 2 Days 30 minutes
• Cheaper
• Smaller samples size
• Self contained test
• Portability
• User-friendly
• Physically preserve biological elements

Research Goals
• Transportation of micro fluids
• Mixing of reagents
• Pumping
• Separation
• Platelets
• DNA
• Research Goals:
• Modelling fluidic flows on
the micro scale when acted
upon by electric fields
• Mapping the velocity of micro
flows
Device on index finger

Device Geometry
ICEO Flow
chamber
125 μm deep
1 mm
20 mm
Gate Electrode
200 μm wide
10 mm
Driving Electrodes

Induced Charge Electroosmosis
(ICEO)
•Electric fields induce charge density on metal surfaces
+
+ -
-
- + - +
- +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires &
Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
+
+ -
-
- + - +
- +
+ -
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires &
Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
+ -
- + - +
-
+ + - - +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires &
Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
+ -
- + - +
-
+ + + - - - +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires &
Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
- + - +
-
+ + + + - - - - +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires &
Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
+ -
- -
+ + + + + - - - - - + +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires &
Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
•Electric fields induce charge density on metal surfaces
•Induced charges cause electric double layer formation
•Electric field becomes tangential
- -
+ + + + + + - - - - - - + +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
- -
+ + + + + + - - - - - -
+ +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
- -
+ + + + + + - - - - - -
+ +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
- + + + + + + - -
- - - - -
+ +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
+
-
--
+ + + + + +
-
- - - -
+
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
+ -
+ -
-
+ + + + -
- - -
+ +
-
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
+ -
+ -
-
+ -
+ + + +
-
-
- -
+
++++++++ ---------+++++++++ --------
Driving
Electrode 1
L
x
Driving
Electrode 2
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
+ -
+ -
+ -
-
+ -
+ + +
-
- +
-
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
- -
L
+
+
+ -
+ -
+ -
+ -
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
-
-
+
+
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
- -
+
+
+
+ -
+ -
+ -
-
-
-
+
+
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
- -
+
+
+
+
+ -
+ -
-
- -
-
+ +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
+ + + + +
+ -
-
- - - -
-
-
+ +
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~
V 0
Floating
For ICEO, see Squires & Bazant, 2004

Induced Charge Electroosmosis
(ICEO)
Electric field sets the double layer in motion
++++++++ ---------+++++++++ --------
Driving
Driving
Electrode 1
x
Electrode 2
L
~ V 0
Floating
For ICEO, see Squires & Bazant, 2004

Wafer Manufacture
•Clean wafer
-Acetone bath
•Apply photo resist
-Even on
centrifuge
•Expose and develop
-UV, Lay out
design
•Deposit Metal
-300nm thick Gold
•Lift off

Final Product

Epi-Fluorescent Microscope
Excitation filter
White light
CCD
Focusing lens
Filter cube
Computer
with μPIV
program
Hg lamp
Excitation light (λ=532nm)
Objective lens
Emitted light (λ=612nm)
Fluorescent particle solution

ICEO EXPERIMENT
1 mm
200 μm
Gate Electrode
Driving electrode 1 Driving electrode 2
~ V 0 =9 V max
Floating
10 mm

Micro Particle Image Velocimetry
•Micro Particle image velocity
• Two images, known Δt
• Sectioning off
• Comparing
• Movement vector

Micro Particle Image Velocimetry
•Micro Particle image velocity
• Two images, known Δt
• Sectioning off
• Comparing
• Movement vector

Micro Particle Image Velocimetry
1 mm
200 μm
Gate Electrode
Driving electrode 1 Driving electrode 2
10 mm
~
Floating
For μPIV, see Meinhart, Wereley & Santiago 1999

Horizontal Velocity Vector Field
10μm
sec

Results!
•Ion filled fluids flow at an average of 10μm/sec
•This is very fast for the micro scale
•Fast enough for use in practical applications
•The flows are in cyclic cycles

Thanks to…
Army Research Lab (for funding)
•
CNSI (for this program)
•
NSF (for funding CNSI and SIMS)
•
UCSB (for hosting all this)
•