Download Final Presentation

Juan David Gutierrez-Franco
Mechanical Engineering
Allan Hancock College
Mentor: Meysam R. Barmi
Advisor: Prof. Carl Meinhart
Mechanical Engineering
1

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-greendemo.blogspot.com/2011/02/lab-onchip-what-is-this.html
2cm
10cm
Microarray
http://i.i.com.com/cnwk.1d/i/ne/p/2
007/fluidigm-007_550x367.jpg 2

The Big Picture
• Mixing chemicals to perform
experiments
Evaporation of solvent
Mixing
Evaporation
3

Goals of the Project
Closed System
• To understand the physics of
electrowetting on open and
closed systems
• To create and test open
surface electrowetting
devices
Open System
• To lower required voltage to
move droplet
• To control the evaporation
rate of the droplet
Evaporation
4

Lab-on-a-Chip mixing chemicals
2.5 mm
Lab-on-a-Chip performing chemical reactions
http://www.chem.utoronto.ca/staff/WHEELER/html/Main.htm
5

Electrowetting
Droplets containing different chemicals need to be
mixed. The movement is done with electrowetting.
6

Research Method: Electrowetting
• Apply voltage to
droplets on chips to
achieve
electrowetting
without electrolysis.
• Try different solution
concentrations,
dielectrics, voltages
and frequencies.
1.5 cm
2.5 cm
7

Research Method: Electrowetting
1M KCl solution 4V 1kHz gold electrode
8

Research Method: Electrowetting
65.0
Contact Angle Change vs. Voltage
f=100 Hz 2.0 M KCl
55.0
Contact Angle Change (°)
45.0
35.0
25.0
15.0
5.0
Electrowetting
Electrolysis
Saturation
-5.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0
Voltage (V)
Saturation is seen once the contact angle does not
change while increasing voltage.
9

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
• 1 M KCl solution showed the lower voltage needed to cause
electrowetting.
• As molarity dropped, electrolysis occurred sooner than
electrowetting.
10

Effect of Molarity on
Electrowetting and Electrolysis
Molarity
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
Molarity vs. Voltage 300 Hz
Electrowetting
Electrolysis
0.0 5.0 10.0
Voltage (V)
KCl solution on gold electrode with no dielectric.
Molarity
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0.00
Molarity vs. Voltage 1 kHz
Electrowetting
Electrolysis
0.0 5.0 10.0 15.0
Voltage (V)
• As molarity and frequency drop, electrolysis occurs
sooner.
11

Molarity Effect on Contact Angle
Change
Contact Angle Change ( )
Contact Angle Change vs. Voltage
f=300 Hz
60.0
50.0
40.0
0.1 M
30.0
0.5 M
20.0
1.0 M
10.0
2.0 M
0.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Voltage (V)
Contact Angle Change ( )
60.0
50.0
40.0
30.0
20.0
10.0
Contact Angle Change vs. Voltage
f=1000 Hz
0.1 M
0.5 M
1.0 M
2.0 M
0.0
0.0 2.0 4.0 6.0 8.0 10.0 12.0
Voltage (V)
• Actuation voltage is same for all cases.
• Saturation is reached sooner by the higher molarity
solutions.
12

Evaporation
Once the droplets are mixed, the solvent needs to be
evaporated.
13

Research Method: Evaporation
• Made of two
layers: Ti/Pt
(200/2500Å)
• Resistance is
measured
Resistive Temperature Detector (RTD)
• Resistance relates
linearly to
temperature
14

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.
Resistance (Ω)
Calibration RTD Sample 1
41.5
41.0
40.5
40.0
39.5
39.0
38.5
296.0 301.0 306.0 311.0
Temperature (K)
Resistivity (nΩ*m)
160.0
155.0
150.0
145.0
R = 0.1532T - 6.6023 140.0
Average Resistivity RTD
295.0 300.0 305.0 310.0 315.0
Temperature (K)
15

Evaporation Time
• Evaporation rate was measured and plotted vs. temperature
Evaporation Rate (nL/s)
5.0
4.0
3.0
2.0
1.0
Evaporation Rate vs Temperature
0.0
305.0 310.0 315.0 320.0 325.0 330.0
Temperature (K)
• As temperature increases, the rate of evaporation of droplets
increases.
16

Summary
•
17

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.
18

Acknowledgments
• INSET Program organizers
• Jens-Uwe Kuhn
• Dr. Nick Arnold
• Prof. Megan Valentine
• Arica Lubin
• Microfluidics Lab
• Prof. Carl Meinhart
• Meysam R. Barmi
• Irvin Martinez
19

Thank you for your
attention
Summer 2011
20

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
22

Contact Angle
• Distance at which the
liquid (droplet) and
vapor (air) interface
meets a solid surface.
• If the angle is:
• >90 surface is
hydrophilic
•

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
24

Electrolysis happening
25

Residue seen on chips
Desired residue
after electrowetting
Residue when
electrolysis occurs
(7V)
Residue when
electrolysis occurs
(100V)
26

Electrowetting Effect
Before
After
27

Before
After
28

Change in diameter of droplet after
electrowetting
~4mm
~5mm
Before
After
29

RTD Cross-Section
• Two layers
• 200 Å Titanium
• Acts as adhesive
• 2500 Å Platinum
30

Peltier Cooler
• 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
31

Evaporation Rate Curve
•
32