Actually, Dow Corning recommends the following for Sylgard 184:

~48 hours at room temperature

45 minutes at 100°C (212°F)

20 minutes at 125°C (257°F)

10 minutes at 150°C (302°F)

Please take a look at its product data sheet. I have attached it for Sylgard 184 from Dow Corning here.

Did you add curing agent? what is the time for baking ? And did you treat the PDMS chip in 1 wash n-pentane / 2 wash of iso-propanol ?

PDMS was prepared at a mixing ratio of 10:1 (base to curing agent). Baking time is around 10h. And I didn't treat with n-pentane and IPA. In fact, I don't know how the treat works. What is it for?

Dear Geunyong,

Based on your explanations, I think your PDMS is not in fact polymer and is an oligomer. I believe, there should be some problems with the cross-link of your PDMS pre-polymer with its curing agent.

Dear Kashaninejad,

In fact, I followed the instruction in data sheet for PDMS.

I used mixing ratio of 10:1, and cured it in 65 degree Celsius for more than 10 hours which is longer time than recommended one.

Is there any problem?

For Sylgard 184 after mixing we put it in oven for less than 120 min at about 70 degrees. I think 10 hour-time for baking is not necessary.

Actually, Dow Corning recommends the following for Sylgard 184:

~48 hours at room temperature

45 minutes at 100°C (212°F)

20 minutes at 125°C (257°F)

10 minutes at 150°C (302°F)

Please take a look at its product data sheet. I have attached it for Sylgard 184 from Dow Corning here.

There should be no problem with the long cure time. I often leave fluidics in the oven over the weekend and they never have problems. Our lab even does a 200OC anneal for 4 hours with no noticeable degradation in optical quality. If the PDMS is mixed well before curing and not tacky when it comes out of the oven, then it is cured.

I would suggest that you may have some structure in the surface of the PDMS that gives you a poor interface between the aqueous phase and the solid phase. This structure could be the cells adhered to the PDMS channels, or may be structure from your casting master that results in a hydrophobic surface that traps small air bubbles that are behaving like an array of disorganized lenses.

You should post some images of the channels with and without the aqueous phase and with and without cells.

Maybe you did not mix properly the PDMS with the curing agent. You have to mix very dynamically and have a lot of bubbles before putting the mix into degasing chamber !