I'm trying to make micropatterns on acrylic to use it as a mold for PDMS. The first time I tried this, PDMS got stuck to the micropattern area of acrylic, even though I made a silanization to the acrylic before spin-coating PDMS on it. I also tried to use glass instead of acrylic, but though I had no problems with the peel-off, the method I'm using to make the pattern was fracturing the glass, so I was searching for a better and more homogeneous alternative to glass.
Any suggestion to improve the peel-off from acrylic or to use another material as a mold are very welcome! Thank you!
You can use SU8 micropatterned film on silicon. You would be able to peel off the PDMS from a few micron features by proper silanization process.
PDMS sticks well to hydrophobic surfaces. Most likely, by silanizing the acrylic you are making it more hydrophobic than it is initially. I would think rather in the direction of making the acrylic surface a bit more hydrophillic, maybe by partial hydrolysis.
Morteza Amjadi and Emanuel Cooper, thank you for your suggestions!
Teflon (PTFE) coating on the mold is a good solution for us. PDMS doesn't stick and you can peel it off without troubles.
Thank you, Andrea Valsesia, I will try your suggestion as soon as possible!
Jinxin Lang, I did not test my PDMS films regarding the elasticity modulus, so I do not know how their modulus will change, sorry!
By the way, how do you do the coating of your mold with teflon, Andrea Valsesia? Do you use spin-coating? Do you anneal the film after spin-coating? Can you give me some indications regarding temperature and time? Thank you!
Teflon is deposited by plasma coating, no experience with spin-coating of this material sorry
Depending on the method of patterning the acrylic, you may be having problems with texture that silanization will not fix. We sometimes use machined acrylic for casting PDMS and often find that the tooling marks make parts difficult to demold. For large scale defects like tooling marks from machining, I like to use PVA as a mold release. It is possible to apply submicron coatings by spin coating using a 2% solution. I also use acetal instead of acrylic if the part does not need to be transparent.
Hi Pan,
I solved the problem by making a treatment of my mold as follows: in a desiccator I placed the mold and a plastic petri dish with 2 drops of trichloro(1H, 1H,2H, 2H-perfluorooctyl)silane and then the mold was desiccated for 30 min. After that the mold becomes much more hydrophobic, so the PDMS films are easily peeled off. When I use the mold for the first time after the treatment, the first film does not peel off so easily (it tends to tear up because it sticks to the mold in some parts). To solve this I just make a thick film so that it does not tear up during the peel off, and then I can peel off thinner films from the mold without any issue.
If you try this approach, let me know if it helped you!
Regards
Hi Andreia,
Thank you so much for illustrating your method in such detailed fashion. I wanted to first try some easy ways, so I simply sprayed some WD-40 on my mold and used compressed air to blow most of it away, with a thin layer left working as a demolder. Then I tried another kind of PDMS in our lab which was softer. And this method turned out to be good as I could pull out my whole device intact.
Thanks anyway for sharing your experience.
Best regards
Hi Pan,
I want to use soft pdms for my devices. Currently, I am using usual one with ratio 20:1. This takes long time to cure. Can you please tell more about this other kind of pdms that is softer?
Hi Andreia dos Santos
Please can I ask you how much was the volume of your '2 drops of trichloro(1H, 1H,2H, 2H-perfluorooctyl)silane'?
Did you keep any specific amount of trichloro(1H, 1H,2H, 2H-perfluorooctyl)silane?
Many thanks
Pan Zuo, you mentioned using a Teflon mold for your PDMS work. Did you happen to try pouring the PDMS over the mold without any coating to the teflon surface? Did PDMS peel off the teflon surface without sticking? I'm up to a similar task now and I was using oil to coat the Teflon before pouring PDMS, but the oil forms an uneven coat and leads to bubbles in the PDMS peel
Apurva Godbole , I just sprayed some WD-40 on the mold and used compressed air to blow most of it off, just as my former answer suggested. This method worked fine for my purpose, though it was a little bit sticky when I tried to peel it off. After some trials, you'll get used to it. My project didn't require me to make very smooth and accurate PDMS stuff, so a little bit bubbles or slightly uneven surfaces didn't matter for me. I recommend you trying to blow most of the oil off, then have a try.
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