Juan David Gutierrez-Franco Mechanical Engineering Allan Hancock - - PowerPoint PPT Presentation

Juan David Gutierrez-Franco Mechanical Engineering Allan Hancock College Mentor: Meysam R. Barmi Advisor: Prof. Carl Meinhart Mechanical Engineering

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Why is microfluidics important?

 Reduction of laboratory size, analysis

time, and sample needed

 Micro Total Analysis System (μTAS)

 Lab-on-a-Chip (LOC)  Microarrays

 Portable and easily controllable

devices for chemical and biological applications

Lab-on-a-Chip (LOC)

http://gigaomized-green- demo.blogspot.com/2011/02/lab-on- chip-what-is-this.html

Microarray

http://i.i.com.com/cnwk.1d/i/ne/p/2 007/fluidigm-007_550x367.jpg

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2cm 10cm

The Big Picture

 Mixing chemicals to perform

experiments

Mixing Evaporation

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Evaporation of solvent

Goals of the Project

 To understand the physics of

electrowetting on open and closed systems

 To create and test open

surface electrowetting devices

 To lower required voltage to

move droplet

 To control the evaporation

rate of the droplet

Closed System Open System Evaporation

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Lab-on-a-Chip mixing chemicals

Lab-on-a-Chip performing chemical reactions

http://www.chem.utoronto.ca/staff/WHEELER/html/Main.htm

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2.5 mm

Electrowetting

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Droplets containing different chemicals need to be

• mixed. The movement is done with electrowetting.

Research Method: Electrowetting

 Apply voltage to

droplets on chips to achieve electrowetting without electrolysis.

 Try different solution

concentrations, dielectrics, voltages and frequencies.

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1.5 cm 2.5 cm

Research Method: Electrowetting

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1M KCl solution 4V 1kHz gold electrode

• 5.0

5.0 15.0 25.0 35.0 45.0 55.0 65.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Contact Angle Change (°) Voltage (V)

Contact Angle Change vs. Voltage f=100 Hz 2.0 M KCl

Research Method: Electrowetting

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Saturation is seen once the contact angle does not change while increasing voltage.

Electrowetting Electrolysis Saturation

Higher molarity solutions show better response to voltage at 1 kHz

Concentration Electrowetting Electrolysis 1 M KCl 4 V 6 V 0.1 M KCl 24 V 16 V 0.01 M KCl 120 V 90 V

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 1 M KCl solution showed the lower voltage needed to cause

electrowetting.

 As molarity dropped, electrolysis occurred sooner than

electrowetting.

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.0 5.0 10.0

Molarity vs. Voltage 300 Hz

Electrowetting Electrolysis Voltage (V) Molarity

Effect of Molarity on Electrowetting and Electrolysis

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KCl solution on gold electrode with no dielectric.

0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 0.0 5.0 10.0 15.0

Molarity vs. Voltage 1 kHz

Electrowetting Electrolysis Voltage (V) Molarity

 As molarity and frequency drop, electrolysis occurs

sooner.

Molarity Effect on Contact Angle Change

12 0.0 10.0 20.0 30.0 40.0 50.0 60.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0

Contact Angle Change vs. Voltage f=300 Hz

0.1 M 0.5 M 1.0 M 2.0 M Voltage (V) Contact Angle Change ( ) 0.0 10.0 20.0 30.0 40.0 50.0 60.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0

Contact Angle Change vs. Voltage f=1000 Hz

0.1 M 0.5 M 1.0 M 2.0 M Contact Angle Change ( ) Voltage (V)

 Actuation voltage is same for all cases.  Saturation is reached sooner by the higher molarity

solutions.

Evaporation

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Once the droplets are mixed, the solvent needs to be evaporated.

Research Method: Evaporation

 Made of two

layers: Ti/Pt (200/2500Å)

 Resistance is

measured

 Resistance relates

linearly to temperature

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Resistive Temperature Detector (RTD)

Calibration of RTD

 Fabrication can alter properties of

the RTD

 Calibration is needed for each chip

 Readings of resistance at known

temperature used for calibration of RTD.

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38.5 39.0 39.5 40.0 40.5 41.0 41.5 296.0 301.0 306.0 311.0 Resistance (Ω) Temperature (K)

Calibration RTD Sample 1

R = 0.1532T - 6.6023

140.0 145.0 150.0 155.0 160.0 295.0 300.0 305.0 310.0 315.0 Resistivity (nΩ*m) Temperature (K)

Average Resistivity RTD

Evaporation Time

 Evaporation rate was measured and plotted vs. temperature  As temperature increases, the rate of evaporation of droplets

increases.

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0.0 1.0 2.0 3.0 4.0 5.0 305.0 310.0 315.0 320.0 325.0 330.0 Evaporation Rate (nL/s) Temperature (K)

Evaporation Rate vs Temperature

Summary



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Future Plans

 Find dielectric that decreases voltage needed for

electrowetting and prevents electrolysis.

 Find way to dewet a droplet after electrowetting occurs.  Control the evaporation rate of the droplet using a peltier

heater and the reading of the resistance of the RTD.

 Combination of electrowetting and evaporation devices.

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Acknowledgments

 INSET Program organizers

 Jens-Uwe Kuhn  Dr. Nick Arnold  Prof. Megan Valentine  Arica Lubin

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 Microfluidics Lab

 Prof. Carl Meinhart  Meysam R. Barmi  Irvin Martinez

Thank you for your attention

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Summer 2011

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Definitions

 Electrowetting: modification of the properties of the droplet’s

surface by applying electricity.

 Modifies contact angle and surface tension.  Surface from hydrophobic to hydrophilic

 Microfluidics: use of small volumes of fluid to perform tasks

(reactions, movement, mixing)

 Free Surface: system where the droplet is in contact with the air.  Hydrophobic: repels water  Hydrophilic: attracts water

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Contact Angle

 Distance at which the

liquid (droplet) and vapor (air) interface meets a solid surface.

 If the angle is:

 >90  surface is

hydrophilic

 <90  surface is

hydrophobic

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Electrolysis

 KCl is present in solution as

ions

 Once voltage is applied,

positive ions (K+) go to the negative electrode and negative ions (Cl-) go to the positive electrode

 K gains an electron

 Forms potassium atoms

 Cl loses an electron

 Forms chlorine atoms

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Electrolysis happening

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Residue seen on chips

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Desired residue after electrowetting Residue when electrolysis occurs (7V) Residue when electrolysis occurs (100V)

Electrowetting Effect

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Before After

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Before After

Change in diameter of droplet after electrowetting

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~4mm ~5mm Before After

RTD Cross-Section

 Two layers

 200 Å Titanium

 Acts as adhesive

 2500 Å Platinum

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Peltier Cooler

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 Used to cool or heat chips.  Positive voltage on red cable

cools the top surface and heats the bottom surface

 Negative voltage on red cable

heats the top surface and cools the bottom surface

Evaporation Rate Curve



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