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 Lab-on-a-Chip (LOC) Micro Total Analysis System ( μ TAS) http://gigaomized-green- Lab-on-a-Chip (LOC) demo.blogspot.com/2011/02/lab-on- chip-what-is-this.html Microarrays 2cm Portable and easily controllable devices for chemical and biological 10cm applications 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 Evaporation of solvent experiments 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 Open System surface electrowetting devices To lower required voltage to move droplet Evaporation To control the evaporation rate of the droplet 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 7 2.5 cm
Research Method: Electrowetting 1M KCl solution 4V 1kHz gold electrode 8
Research Method: Electrowetting Contact Angle Change vs. Voltage f=100 Hz 2.0 M KCl 65.0 55.0 Contact Angle Change (°) 45.0 Electrolysis 35.0 Electrowetting Saturation 25.0 15.0 5.0 -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 vs. Voltage 300 Hz Molarity vs. Voltage 1 kHz 2.00 2.00 1.75 1.75 Electrowetting Electrowetting 1.50 1.50 Molarity Molarity 1.25 1.25 Electrolysis Electrolysis 1.00 1.00 0.75 0.75 0.50 0.50 0.25 0.25 0.00 0.00 0.0 5.0 10.0 0.0 5.0 10.0 15.0 Voltage (V) Voltage (V) KCl solution on gold electrode with no dielectric. As molarity and frequency drop, electrolysis occurs sooner. 11
Molarity Effect on Contact Angle Change Contact Angle Change vs. Voltage Contact Angle Change vs. Voltage f=1000 Hz f=300 Hz 0.1 M 60.0 60.0 Contact Angle Change ( ) Contact Angle Change ( ) 0.5 M 50.0 50.0 1.0 M 40.0 40.0 0.1 M 2.0 M 30.0 30.0 0.5 M 20.0 20.0 1.0 M 10.0 10.0 2.0 M 0.0 0.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 Voltage (V) 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 Resistance relates Resistive Temperature Detector (RTD) 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 . Average Resistivity RTD Calibration RTD Sample 1 160.0 41.5 Resistivity (n Ω *m) 41.0 155.0 Resistance ( Ω ) 40.5 150.0 40.0 39.5 145.0 39.0 R = 0.1532T - 6.6023 140.0 38.5 295.0 300.0 305.0 310.0 315.0 296.0 301.0 306.0 311.0 Temperature (K) Temperature (K) 15
Evaporation Time Evaporation rate was measured and plotted vs. temperature Evaporation Rate vs Temperature 5.0 Evaporation Rate (nL/s) 4.0 3.0 2.0 1.0 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 Microfluidics Lab Jens-Uwe Kuhn Prof. Carl Meinhart Dr. Nick Arnold Meysam R. Barmi Prof. Megan Valentine Irvin Martinez Arica Lubin 19
Thank you for your attention Summer 2011 20
21
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 <90 surface is hydrophobic 23
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 Residue when Residue when after electrowetting electrolysis occurs electrolysis occurs (7V) (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
Recommend
More recommend
