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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)

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