I am planning to use polydimethylsiloxane (PDMS) to create a phantom for mimicking tissue for imaging. For this, I plan on using SYLGARD® 184, which is a viscous liquid. When adding other components to it, air bubbles will be introduced.

I have learned that one way (available to me) to remove bubbles / de-gas the solution is by using a vacuum pump to create negative pressure. What negative pressure is sufficient to remove the air from the gel-like solution?

  • $\begingroup$ The answer will also depend on the amount of time the negative pressure is applied. $\endgroup$ – Chris Mueller Mar 20 '15 at 16:35
  • $\begingroup$ @ChrisMueller I would want to limit it to less than one hour. Any practical suggestions? $\endgroup$ – Nazar Mar 20 '15 at 17:18
  • $\begingroup$ Use an old vacuum and find out. If the negative pressure is too strong, introduce a leak into the system; if it's too weak you need a bigger vacuum or you have a leak. Just remember that vacuums use the airflow through them to cool themselves and you will be putting a lot of load on the pump to maintain a negative pressure, so make sure you don't fry it by running it for too long consecutively. $\endgroup$ – thepowerofnone Mar 20 '15 at 17:22
  • $\begingroup$ @thepowerofnone Here I found a good size vacuum desiccator, so I hope after getting some negative pressure, I can just close the valve and let it stay. It should hold the vacuum up to 24 hours. At this point I just need to select a reasonably strong pump, so I would like to know what minimum negative pressure it should create. $\endgroup$ – Nazar Mar 20 '15 at 17:37
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    $\begingroup$ Practical tip. As the the dissolved gas leaves the resin, it may cause the resin to foam-up and overflow the bucket. Use a bucket that's 2x the volume of your batch. It may also help to outgas gradually. $\endgroup$ – Nick Alexeev Mar 21 '15 at 5:03

15-30 mins under any vacuum pump will be fine. If there are any air bubbles still there at the surface I recommend to burst it with pressurized air gun. Make sure that your vacuum chamber lid is sealed well. Some time it is useful to use vacuum grease to achieve that.

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