Hello,

Or vapor of HMDS...

And be sure your aperture in the mould has a smaller diameter inside compare to the entrance... if not... critical...

I think 10:1 is fine. Use TFOCS (Tridecafluoro-1,1,2,2-tetrahydrooctyl-1-trichlorosilane) vapor for coating, then will be easy to peel off PDMS. My PDMS pillar is not so small.

Even if you coat the silicon wafer with perfluorosilanes which should deliver the best demolding performance you may still encounter breaking of the PDMS pillars 500 nm thick and 1 um tall. Looking forward to your follow up on the result. Good luck.

For 10:1 aspect ratio, I think the stripping solution mentioned by Ryuji should work just fine for you. However, the difficulty is getting the solution down into the pit bottom of the mold. Due to air entrapment, sometimes the solution does not sink to the bottom, resulting in some pillars being damaged during stripping. Anyway give it a shot, and good luck.

I root for Weian Sheng's TFOCS vapor coating. Vapor penetration into narrow pits on the mold is better than that of solutions.

Hi Paul, you could try to coat your mold with parylene C using chemical vapor deposition - will help a lot to keep your features on the mold and on the PDMS. Way more reliable than any silane based coating. It's thicker (nm range) but can be controlled fairly easily. We published a paper about it if you want to have a look: http://pubs.rsc.org/en/content/articlehtml/2011/lc/c1lc20623k

Hi Paul, you could try to decrease the surface energy by treat the mold wiht FOTS via vaporing. Low surface energy is help for demolding. But have you ever calculating the maximum AR of PDMS pillars from demolding? I think 10:1 is too large to demold for PDMS. There's a paper about PDMS naopillars from AAO. This paper reported that the largest AR is ~7 with a diameter of 150nm.

Thanks for the ideas, everyone. I've mainly coated my mould with silane in solution before - I'll switch to vapor deposition for these high aspect structures and let you know how it goes.

Kevin, parylene C looks ideal, but I don't have the equipment to try it out. I do have access to a plasma polymerisation setup, but from a quick google I don't think that's sufficient for the same type of deposition.

Hi, if you choose to use perfluorosilanes as a release agent, simple desiccator can do the trick - probably the least costly solution, provided you have a vacuum pump handy.

Hi, May I ask if you have already a solution?

I cast micropillars of AR ca. 14, but the height is about 240µm. Now I suffer from the peeling process that the pillars are always torn apart and get broken in this process.

Does anyone have an idea concerning how to peel them off gently and properly?

Thanks!

Yiou Liu, have you tried different ratios of crosslinker during PDMS-preparation? Oh, post from 2014 ;) - what was your solution by now? Best, Martin

Yiou Liu please see this article :

Article Fabrication of a Polymer High-Aspect-Ratio Pillar Array Usin...