I mean realistically each layer line is 25ums at best so at the <10um level it’s gonna be bumpy no matter what. I’ll take some microscope images today of the mold and the PDMS cast and post them. GOnna be a few hours before they’re ready. I’m curious about it myself. I’m using the PDMS as a chemical reactor for nanostructure polymers. Don’t really care about the surface (at the moment - maybe it’s important in some way). Another thought I had is to try releasing the PDMS from the mold when it’s 80% cured. hypothesis: You might get a surface relevelling effect. Maybe worth a quick scan in the literature. I say this because I was impatient and released my PDMS too soon. I ripped it in one place during the detachment process. But when I checked a few hours later I couldn’t find the rip. The PDMS had self healed. I’m gonna check again for the rip and make sure I wasn’t dreaming.
Mold surface (greenish images) at 4x and 10x . best zoom I could get given geometry of microscope and mold itself.
PDMS orange coloured images at 4x and 10x (PDMS is transparent so used transmisision light not reflection). Can make out layer lines in some images.
The two scale bars on the wide area orange PDMS image should be like to 500um bar in the first green one.
Thanks a lot for the images. I think the 2nd orange PDMS image shows pretty rough surface of grey pro rein. I am experiencing the same with standard grey resin. I got the same kind of surface features with microscope.
https://pdfs.semanticscholar.org/8718/657a2b13dc22c7913ded5f22b998d7de7f7b.pdf look everyone! A paper on using clear and flexible resins as PDMS molds
I have the same problem: silicone does not catalyze. Has anyone found a definitive solution?
infinitely thank y
Just tried casting PDMS in Standard Gray.
I did a 5 min dirty IPA wash + 5 min clean IPA wash,
Followed by 0.5-1 h in a Gel Nail Curing UV chamber,
Then finally a wash with dish soap + water
Overall the PDMS cured fine, the only thing was a coating/thin layer of what seemed to be uncured PDMS on surfaces that were in direct contact with the mold. Maybe this just happens with the first casting as remnant resin reacts with the PDMS. I’m guessing that it can also be cleaned off during post-cleaning of the casted PDMS.
I might try some more things like soak the parts in water before washing with dish soap as OP suggested. Or maybe leave the part in the UV chamber for longer since I’m not using the official UV/405 nm curing equipment.
from the paper in post by play150:
“Since the PDMS cannot be polymerized into a cured part in contact with the surface of the molds, they are treated with oxygen plasma at high power (Harrick Plasma, Inc.) before molding for 2 min and then the parts are coated with fluorinated silane (Trichlorosilane, SigmaAldrich, Inc.) for 6 hours at 60 °C. Consequently, the cured parts will be removed easily from the master mold and the surface will not be not sticky…”
Interesting! I must’ve missed this when reading
This is exactly what “Curing inhibition” means. The PDMS within 0.2mm to the interface of the resin fails to cure, indefinitely, regardless the time and temperature.
I cured my grey molds in Form Cure and left for a week before the molding, and it still fails the curing.
There has to be some surface prep. Or some resin may work better, may be grey pro or model?
I am troubled too by this issue. Didn’t realize it was the curing inhibition from the mold after quite many failures to cure PDMS even at 110 degree C.
I only used Grey V4 on Form 3 and it was IPA washed, UV cured and even sanded multiple times for surface finish. Yet the PDMS region very close to the grey resin still remains tacky. The mold itself is also ruined because of this half-cured PDMS layer that gets transferred to everywhere it touches.
I guess I’ll start with some clear coat spray. But I am worried that the coat applied contains inhibitor for PDMS , too. Since I probably don’t have access to any airbrush, I would try spray can or dipping in a container.
Sylgard 184 lists urethane containing material inhibiting the curing. Does this mean I should totally avoid using polyUrethane clear coat?
Others in the thread have mentioned mold release spray
I have had good success casting platinum silicone (Ecoflex 00-20 specifically) into Grey V4 after a 2 stage IPA wash and 4 hour 60c cure with UV. I also ensure I use clean IPA that has never touched problematic resins. I found that if the IPA had washed Draft parts curing was a problem.
Hmm. Interesting. Guess different silicone is affected differently by the resin surface. I use Form Wash so I cannot guarantee I can replace 8L fresh IPA every time I print something.Though I always rinse the washed part thoroughly with a pure IPA wash bottle afterwards. Unfortunately That does not solve the curing issue for me.
I also deliberately reduce the curing temperature because my part geometry makes it very easy to bend after being heated at 60C for just 20 mins.
Sometimes I even rinse the part surface with acetone… and it stills messes the PDMS curing