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.
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
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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+
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
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
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)
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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