Hello everyone,
I am using multilayer soft lithography to fabricate microfluidic devices. I am struggling to align the PDMS layers using a stereo microscope since both of the layers stick together and eventually do not move.
Is there a way to prevent them to stick with each other and align them eventually?
Read this article..
Article Finger-Powered Microfluidic Systems Using Multilayer Soft Li...
After plasma, add some ethanol between the two layer to align. It will lubricate the PDMS, allowing you to precisely align them. You'll just have to wait for the ethanol to evaporate. In my experience, the plasma bonding is still fine after that.
Bastien Venzac I have tried adding methanol and it resolved the problem of PDMS being sticky. However, the bonding did not work. I will try ethanol next time. Do you have any recommendations on how to avoid this issue?
I am working on on-ratio bonding. Both of the layers have 10:1 (base:curing agent) ratio.
You still need to add the ethanol quickly after the plasma treatment... Align, wait for the ethanol to evaporate. After less than a minute, the PDMS will be in contact and you can then move everything to an oven (an extra 15min, 60°C enhances the bonding).
However, PDMS bonding via plasma has always been for me the less reproducible step ever in soft-lithography ; and I worked in 6 different labs with 5 different plasma systems... Is your bonding OK and strong usually?
I have not yet tested with ethanol but I have tested with water.
I treat the device and a glass slide with argon plasma at ~100 mtorr for 3 minutes followed by quickly adding a few drops of water and aligning the PDMS layer on the glass slide followed by placing the device on a hotplate for ~20 minutes. The bonding works. However, PDMS-PDMS bonding is not very efficient using this approach.
Short thoughts about that:
- for PDMS bonding, I have mostly seen air or oxygen plasma, not argon. Argon plasma is used for cleaning (as it has a physical effect), while you are more searching for a chemical activation. I have no experience with argon plasma bonding, maybe check if in the literature it's used or not for that application.
- Going that line, plasma duration and power is really important. Even with air plasma, if your plasma is too long or too powerful, you will both activate the PDMS chains but also break them. Results: the short activated chains will stick super well to your second substrate, but they will also detach from rest of the PDMS part...
Some papers that might help you:
http://iopscience.iop.org/1742-6596/34/1/026
Article NOTE: Determining the optimal PDMS PDMS bonding technique fo...
Article Experimental study of PDMS bonding to various substrates for...
I remember in our lab we used the ethanol trick to align them, but only if it is completely critical, because as others mentioned, the bonding may not work as well. I ended up just doing it by eye and getting better at it, as it worked for my applications (I was making valves to block certain channels, and I left myself room for error).
I have found that 3D printed PLA guides have worked well for moulding and aligning PDMS chip layers. Glad to share a sample file.
Thanks everyone for answering. These are definitely helpful. I will try integrate these in my next experiments.
Christine Poon I would highly appreciate that. I have sent you a PM.
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