When to incorporate cyclomethicone (cyclopentasiloxane)

It is my understanding that due to its volatility cyclomethicone should be incorporated in the emulsion at low temperatures; and therefore I always add the cyclo at 45oC or below, which is an issue with emulsions that increase their viscosity at they cool.

Recently, I came across a few formulations in which cyclomethicone is added initially to the oil phase that is then heated to 80oC.
By doing this, wouldn't the cyclomethicone evaporate to a large extent?


  • You typically cover/seal the vessel you are heating your oil phase in as you would a water phase to mitigate evaporative loss. 

    If D5 is the only volatile chemical in your oil phase, you could also "QS" it just prior to phase combination (weigh the vessel or phase to find out how much D5 you lost, then add that amount into the phase).
  • @Laskedbetter

    That is interesting and great information! I too always added the cyclomethicone and other silicones in the cool down phase (below 40oC). I also don't cover my vessels which I honestly never thought of doing. Normally I would just "QS" the water phase at the end or add more in the beginning to compensate. Thank you for that gold nugget.
  • RubenRuben Member
    edited March 2015
    Is adding the volatile ingredients to the heated phase before heating and then replacing what has been lost a common practice in the industry? I assume that to do this you need to heat in closed vessels, don't you?

    The evaporation problem is only with low molecular weight silicones, such as cyclomethicone and low MW dimethicone. Other silicones, for instance dimethicone 350, can be added directly to the heated phase.
  • CosChemFanCosChemFan Member
    edited March 2015
    @Ruben Thank you for that information. I understood that before, however; anytime I have added silicone during the heating phase the silicone always coagulates and I end up just removing the pieces from the formula. It's happened to me every time I've added it to my oil phase. I typically heat my oil phase to about 80-85oC per what I've learned as standard operating procedure. After having this happen to me a few times I researched this phenomenon a bit. To my understanding, silicone doesn't handle temperatures above 60oC and cyclomethicome doesn't like temperatures over 100oC. That is why I always added My silicones at or below 60oC. Not trying to hijack your thread, just responding to you.
  • RubenRuben Member
    I think I answered my question to a large extent. I did a little bit of
    digging and found that D5 has a boiling point of around 215oC. So it is
    even less volatile than water. Still some evaporation at 80oC can be
    expected if heated for a long time.

    Then I asked myself if the boiling point is so high, why it is claimed that the dry feel of cyclomethicone (D5) comes from its high volatility. I did a little bit more digging and found this interesting article.

  • @Ruben The answer regarding whether it is industry standard to "QS" is yes and no. I have worked in companies that do this and companies that don't. 

    In a foundation I developed a few years ago, we had to do some significant shade adjusting in all of our first production batches and there was very little consistency in how the shades appeared. I noticed that the processing times were extremely variable, so I added a "qs" step for D5 and water before phase combination and saw much better consistency after that.
  • Bill_TogeBill_Toge Member, Professional Chemist
    @Ruben also, in my experience cyclomethicone is a lot less volatile as part of a mixture than it is on its own 

    one way of gauging loss on heating would be to heat your oil phase (just your oil phase) to the temperature you intend to emulsify it at, holding it there for a while, and watching to see if any visible vapour comes off

    and if you weigh the container before and after heating, you can make it a quantitative test
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • Chemist77Chemist77 Member, PCF student
    @Ruben Great article that, a clarification of widely accepted misconception.
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