Apart from plasma activation, PDMS can be made hydrophilic by treating it with Piranha solution (and maybe KOH in an elaborate approach).
I found two papers reporting this effect. Interestingly, both report very different treatment times.
The following suggests treatment in the order of 30-60 seconds for efficient PDMS-PDMS bonding using Piranha activation:
Koh, K.-S., Chin, J., Chia, J., & Chiang, C.-L. (2012). Quantitative Studies on PDMS-PDMS Interface Bonding with Piranha Solution and its Swelling Effect. Micromachines, 3(4), 427–441. http://doi.org/10.3390/mi3020427
Another paper reports treatment times >10 minutes for increasing hydrophilicity of the PDMS:
Maji, D., Lahiri, S. K., & Das, S. (2012). Study of hydrophilicity and stability of chemically modified PDMS surface using piranha and KOH solution. Surface and Interface Analysis, 44(1), 62–69. http://doi.org/10.1002/sia.3770
Contact angle and bonding strength are both linked to the amount of Silanol groups. However, both papers give very different suggestions on the treatment time.
Is there any other hands-on experience on treatment time with Piranha for generating a hydrophilic surface of PDMS?
Best
Georg
At room temperature, 3:1 (H2SO4:30%H2O2), it can vary from 30-300 seconds before oxidation causes the clear, surface PDMS to become opaque white. Further oxidation causes the surface PDMS to become rippled. We run a small test in the corner of each sample to check before we oxidize the larger surface. We think the variation comes from variation in the batches of the PDMS, differences in curing times and curing temperature, and temperature of the piranha solution itself during oxidation. (We cool it to room temperature before use.)
The surest way to find out is to try both methods yourself. The two papers use slightly different formulations of the Piranha solution (3:1 and 2:1), which might partially account for the difference in exposure times. Also, it simply could be that the second paper decided to go for "overkill", or that the first paper was focused on bonding, and did not need 100% surface silanol coverage.
At room temperature, 3:1 (H2SO4:30%H2O2), it can vary from 30-300 seconds before oxidation causes the clear, surface PDMS to become opaque white. Further oxidation causes the surface PDMS to become rippled. We run a small test in the corner of each sample to check before we oxidize the larger surface. We think the variation comes from variation in the batches of the PDMS, differences in curing times and curing temperature, and temperature of the piranha solution itself during oxidation. (We cool it to room temperature before use.)
Hi all,
I try to find an easy way to add OH groups to PDMS, even break of the Si-O-Si is acceptable, thus giving lower Mw molecules. Final purpose is to have cost effective material for hydrophobization of lass. Any ideas how to start - HNO3, H2SO4, H2O2...with 60 - 80 deg heating?
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