an inexpensive method for pdms-pdms bonding in fabrication of microfluidic device koh kai seng, the...
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AN INEXPENSIVE METHOD FOR PDMS-PDMS BONDING
IN FABRICATION OF MICROFLUIDIC DEVICE
Koh Kai Seng,The University of Notitngham Malaysia Campus
The Second Conference on Advances in Microfluidics and Nanofluidics and Asian-Pacific International Symposium on Lab on Chip5th-7th January 2011, Singapore
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TABLE OF CONTENT
Introduction Experiments Result and discussion Conclusion
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INTRODUCTION
Poly(dimethylsiloxane) (PDMS) has been widely used in microfluidic applications.
Sealing has been the key challenges in microfluidic fabrication. Reversible bonding, irreversible bonding.
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Reversible bonding Irreversible bonding
Reusable. Not reusable.
Able to sustain low pressure Able to sustain relatively high pressure (200-700kPa)
Natural bonding Surface property modification.
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Conventional sealing techniques require Costly equipments.(Oxygen plasma) Time consuming. (Partial curing technique) Involve complicated steps. (Oxygen plasma) Reliability and repeatability are always at the
centre of argument.
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Piranha solution is used because More economical, Time saving, Involve less complicated steps. Relatively high reliability and repeatability
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BONDING MECHANISM
First stage: Dehydration of hydrogen and oxygen into water
unit.
Second stage: H2SO4 + H2O2 → H3O
+ +H2O4- + O∙Reactive atomic
oxygen species
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+
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Bonding mechanism:
Si O Si O Si
CH3
n
PDMS surface
O∙
O∙ → H2O → OH- + OH-
CH3O·
OH-
OH
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EXPERIMENT METHOD
Sealing procedure: PDMS samples with strings embedded in it were
solidified. The samples were cut into 2cm × 2cm square piece
each.
Piranha solution concentrated Sulfuric acid (96wt%) & Hydrogen peroxide(30wt%) at 3:1 weight ratio.
Interfaces of two PDMS are drenched into the solution for a define interval.
Next, both surfaces attached and bounded together followed by thermally curing of 70°C for 60 minutes.
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RESULT & DISCUSSION
2 methods are used to test bonding power:• Tensile strength test• Leakage test
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Drenching time (sec)
Tensile strength (kPa)
1 2 3 AveageStandard
Deviation (%)
0 20 13 24 19.00 29.30
15 69 59 72 66.67 10.21
30 102 94 100 98.67 4.22
45 189 200 217 202.00 6.98
60 125 132 124 127.00 3.43
75 32 50 54 45.33 25.85
Table 1: Tensile strength (kPa) against drenching time (sec) at 3:1 weight ratio of Piranha solution
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Table 2: Calibration of tensile strength of string (kPa)
MaterialTensile strength (kPa)
1 2 3 Average
String 500 473 486 486.33
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PIRANHA SOLUTION USING HNO3
(65WT%) + H2O2 AT 3:1 WEIGHT RATIO
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Drenching time (sec)
Tensile strength (kPa)
1 2 3 Aveage
Standard Deviation
(%)
0 20 25 24 23.00 11.50
15 32 28 34 31.21 10.21
30 48 44 47 46.19 4.22
45 59 62 58 59.45 3.43
60 88 94 102 94.57 6.98
75 72 87 72 76.82 11.22
Table 3: Tensile strength (kPa) against drenching time (sec) at 3:1 weight ratio of Piranha solution
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Figure 1: Graph average tensile strength (kPa) against drenching time (sec)
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Sustaining time of the PDMS-PDMS interfaces is within the range of 20-30 seconds.
0 10 20 30 40 50 60 70 800
50
100
150
200
250
Graph Tensile strength (kPa) against sealing time (sec)
Surfuric acid(96wt%)Nitric acid(65wt%)
Drenching time, (sec)
Tensile s
trength
,(k
Pa)
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Optimum drenching time is 45 seconds. Reaction ends at around 65±5seconds.
Pure Sulfuric acid remains. (limiting reactant is Hydrogen peroxide). PDMS surface will be attacked.
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Leakage test Water is pumped into closed channels for 5
minutes at 5,20,50µl/min. No leakage detected!!
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CONCLUSION
An inexpensive polymer-based sealing technique, using piranha solution (3:1 weight ratio) is demonstrated and quantitative result is shown.
This irreversible bonding techniques is able to sustain a mechanical strength of (200±20kPa).
Water is injected into closed microchannels at different flowrates and no leakage occurred up to a flowrate 0.3ml/hr.
In future work, optimization of the bonding strength using the same method will be investigated.
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THANK YOU FOR YOUR ATTENTION.
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