I would personally amend 2nd and 6th steps, so the procedure would look something like:

1. Mix base and curing agent (10:1) [make uniform throughout the beaker].

2. Leave it to degas [usually takes around 4 hours at the room temperature].

3. Pour into the mold.

4. Leave for an extra hour or so [check if there are no bubbles trapped in the solution]

5. Cure [In the oven, 75-80 C for 4 hours should be enough, it really depends of the applications]

6. Cut the PDMS

7. If you need to clean the surface, I would suggest duck-tape, rather than a solution based cleaning [I guess it might depend of the application].

Hopefully that would help,

Good luck!

hi,

THe blurriness may be arising due to trapped micro air bubbles which are present due to insufficient degassing. Or it is due to the walls of the mold which are being imprinted on the surfaces of the pdms. If the walls are not optically smooth, the irregularities from the walls will be imprinted on the pdms which causes blurriness in it. Secondly the greasy feel on the surface of the pdms after you complete the fabrication step may be due to improper mixing of the elastomer and the curing agent. Make sure that each corner/crevices of the mixing vessel is properly stirred so that the curing agent reaches all parts of the elastomer thoroughly.

I recommend the 7th step suggested by dimitars for cleaning the PDMS surface after the fabrication process.

Regards

I use NuSil silicones (in UK see: http://www.silicone-polymers.co.uk/) and a wide range are available from very hard to very soft after cure. The typical cure schedule can be from 100°C for 30 minutes to 150°C for 5 min. I tend to use the 100° end of the schedule and after the 30 minute cure let it ramp-down to room temperature over several hours before disturbing the set-up.

Greasy and sticks sounds like not sufficient mixing. I use a Speedmixer for this (in UK see: http://www.speedmixer.co.uk/) The high G, shearing action of the mixer will mix to a totally homogeneous mix in less than 5 minutes and the shearing action is very effective for degassing at the same time. Vacuum degassing can also be used after this, if preferred, but I have found it is not needed.

Since using the Speedmixer, I have never had a problem with sticky/greasy finish.

I would follow Dimitars method ensuring that glassware/mould is clean. Solvents can swell PDMS making it appear cloudly; although I am not sure about acetone or isopropanol. Depending on time restrictions you do not need to apply heat and can leave over night.

An example procedure could be:

1) mix your curing agent and base well - visually lots of small bubbles,

2) pour into clean glassware (ensuring no big bubbles),

3) check after a few hours (removing any big bubbles)

4) leave overnight and,

5) slowly remove PDMS substrate.

As for the grease, I think it mostly depends on how good you mix and cure your PDMS. Sometimes when PDMS cures at RT, it appears sticky. However, the parameters you mention here are pretty normal to me.

What is your template for molding? I had greasy, uncured PDMS residues when I used PMMA to enclose my master.

A second degassing step after pouring the mixture on the master could make molding more efficient.

And WHY DO YOU MANIPULATE your PDMS with those solvents?? PDMS is a weird polymer and it absorbs molecules that often lead to changes. The best way to use PDMS is fresh from the master and in case you got some particles on it, just remove it with a tape.