Repeating monomer of SiO(CH3) units.

Polymerization causes cross linking.

Visco elastic polymer (Based on ‘n’).

Intrinsically hydrophobic.

Biocompatible and Oxygen permeable.

H3C[SiO(CH3)2] nSi(CH3)3

Variety of Applications

Micro fluidics• Molds

• Devices

• Brain Slice Device

Microfluidic Devices

Hydrophobic because of the methyl groups.

Applications of PDMS require it to be hydrophilic.

Increased cell adhesion and less repulsion when incubating sample.

Hydrophilicity due to

Addition of a Silanol group.

Alteration of surface Chemistry.

Never regains its original hydrophobicity due to permanent scarring of surface.

Before Plasma Activation

After Plasma Activation

Erratic Behavior of PDMS after plasma activation.

Major instrumentation : plasma chamber.

Non uniform activation of plasma.

Variation – Humidity, atmospheric pressure, flow rate

1.5 CM

Vacuum Chamber

Schematic Representation of the Plasma Chamber

Spatial Location vs Contact Angle

22273237424752576267

1 2 3 4 5 6 7 8

Spatial Placement in Chamber

Con

tact

Ang

le

Least Hydrophobic = Best Area

Quantification Experiment

– Samples were not aged (10 per time frame).

– Bonding and contact angle was measured.

– Since the samples were not aged, could be used as a control

– Image J is used for measuring contact angles

Image J

60 PDMS samples

1 hour (10 samples)

2 hours (10 samples)

4 hours (10 samples)

5 hours (10 samples)

6 hours (10 samples)

3 hours (10 samples)

Contact angle Measurements

Quant. Bonding Measurements

PLASMA

ACTIVATION

Bonding vs. Time

1.3

5.2

10 9.58.3

5.3

0.9

0

2

4

6

8

10

0 1 2 3 4 5 6

Time (Hrs)

Qua

ntita

tive

Bond

ing

Str

engt

h

p < .005

Time frame of interest

Contact Angle vs. Time

21.2569

10

27.924734.6016 34.9736

42.175746.5485

9141924293439444954

0 1 2 3 4 5 6

Time (Hrs)

Cont

act A

ngle

(Deg

rees

) p < .0005

Time frame of interest

Contact Angle and Bonding Variation with Time

0

2

4

6

8

10

12

0 1 2 3 4 5 6

Time (Hours)

Qua

ntita

tive

Bon

ding

St

reng

th

10

15

20

25

30

35

40

45

50

Cont

act A

ngle

(D

egre

es)

Bonding Contact Angle

Time frame of interest

Test the effect of ageing after plasma activation.

Ageing before plasma activation decreases the rate of hydrophobic recovery.

Five samples for each time frame.

Compared to the control/quantification experiment.

In - house goniometer

Contact angle on a perfectly hydrophobic surface

60 PDMS samples

1 hour (10 samples)

2 hours (10 samples)

4 hours (10 samples)

5 hours (10 samples)

6 hours (10 samples)

3 hours (10 samples)

Contact angle Measurements

Quant. Bonding Measurements

PLASMA

ACTIVATION

A

G

E

I

N

G

Contact Angle vs Time

020406080

100120

1 2 3 4 5 6

Time (Hrs)

Cont

act A

ngle

(D

egre

es)

Aged Sample (1 hr) Aged Sample (2 hrs) Unaged Sample/ Control

Ageing after plasma activation increases the rate of hydrophobic recovery.

No significant difference between 1 hour aged samples and 2 hours aged sample.

Indicates that although ageing does have an effect, beyond a certain time frame, length of ageing does not matter.

• Self contained environment for micro fluidic liquids.

• Exploits PDMS’s strong affinity for Aluminum.

• Non uniform surface of Aluminum causes

The NSF and DoD for funding this work through grant number CTS 0630470

This project would not have been possible but for the patient oversight of Professor David Eddington and Dr. Javeed ShaikhMohammad. Their constant support and encouragement was invaluable in the completion of this line of research.

D. Bodas, C.k. Malek, Hydrophilization and Hydrophobic recovery of PDMS by oxygen plasma and chemical treatment – An SEM investigation, Sensors and Actuators B 123 (2007) 368-373.

B.H. Jo, et al., Three-dimensional micro-channel fabrication in polydimethylsiloxane (PDMS) elastomer, J. Microelectromech. Syst. 9 (1) (2000) 76–81.

J. Kim, M.K. Chaudhury, M.J. Owen, Hydrophobic recovery of polydimethylsiloxane elastomer exposed to partial electrical discharge, J.Colloid Interface Sci. 226 (2000) 231–236.

J. Kim, et al., The mechanisms of hydrophobic recovery of polydimethylsiloxane elastomers exposed to partial electrical discharges, J. Colloid Interface Sci. 244 (1) (2001) 200–207.

D. T. Eddington, et al., Thermal aging and reduced hydrophobic recovery of Polydimethylsiloxane, Sensors and Actuators B 114 (2006) 170-172.