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Microemulsion too thin

I've been experimenting with my mamey cream formulation now and then, which has evolved a bit. Because I have some Silsense DW-18 in stock, I noted it can be used to make microemulsions and also acts as a co-emulsifier.
The cream without the Silsense was OK but I wanted it thicker, so I made the following changes:

INGREDIENT~~~~~~~~~~OLD~~~~~NEW
mamey oil ~~~~~~~~~~~~~5%~~~~~~5%
cetearyl alcohol ~~~~~~~~~3%~~~~~~5%
cetyl alcohol ~~~~~~~~~~~1%~~~~~~2%
stearic acid ~~~~~~~~~~~~1%~~~~~~2%
vitamin E ~~~~~~~~~~~~~0.5%~~~~0.5%
Silsense DW18 ~~~~~~~~~0%~~~~~0.7%
fragrance 0.2%
glycerol monostearate ~~~~~2%~~~~~2%

The polar components include water at 79% glycerin at 3% and panthenol at 1%.

The result of the changes was that the cream became thinner, rather than thicker. In fact it is so thin it is easily pourable at room temp. The sensorials apart from its watery nature are good, it absorbs quickly and leaves a really luxurious skin sensation. I've got 16.5% of nonpolars including emulsifiers in there, and it's this thin? Presumably it is the silicone ester or microemulsion that's caused this? Looking for opinions.

Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.

Comments

  • OK, here's how I try to visualize problems like this - Imagine that you have a beaker full of very light marbles, with fluid covering them and filling in all the gaps. Now, the surface of the marbles is also a bit sticky, so when you try to stir the marble/fluid mixture, there's some resistance, as the marbles stick to and separate from each other.

    Next, reduce the size of the marbles, but imagine that they stay suspended in place. There's an increased layer of fluid around each marble. The marble/fluid mixture moves much more smoothly as you stir it, because the marbles have more room to move around, and run into each other less frequently.

    That's what you're doing with your microemulsifier, which is specifically designed to make your inner-phase oil droplets (marbles) smaller, and reduce the "stickiness" of the droplets as well. Every microemulsion I've ever encountered was water thin, by the way.

    The easiest way to compensate for this is to make your continuous (water) phase more viscous. This will have the added side benefit of making your emulsion more stable.
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • Every microemulsion I've ever encountered was water thin, by the way. 
    Wow. I wish I had known this before.
    Is there any actual benefit to using a micro emulsion? I'm wondering whether to continue along that route or not. I guess if I do, I am going to have to either use a carbomer or an alternative thickener such as Glucamate VLT.
    Thanks for the explanation!
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • If you need a sprayable emulsion, microemulsions are awesome.
  • @Iaskedbetter: Thanks for that. Such a product had not occurred to me. Is there any benefit to the skin from a microemulsion rather than a regular one?
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • From a formulators perspective I think the primary advantage is creating unique formula types. Thin functional liquids, sprays, serums, etc. are less common formulation types so it is easy to find unique ideas using these types of "vehicles", which is where microemulsions shine.

    Functionally, I believe there is research suggesting that microemulsions can penetrate into deeper layers of the skin compared to regular emulsions. If you pair the formula with liposomes loaded with an "active" substance, you might find that using a microemulsion enhances the activity of your "active".
  • The thought of jettisoning the classic 2 oz cosmetic jar for a spray bottle is quite interesting. There's an immediate advantage in terms of preservation. I'll have to research my packaging sources to see what the availability and costs look like. Thanks for the idea. I do like the sensorials that the silicone ester produces - days afterwards you can still detect the silky feeling.
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • Maybe I should make it into a different product. "Satin Skin for a Nite of Delite"
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • Hey belassi,
    the formula you created before was a macroemulsion?
    I have heard that microemulsions are almost clear, with blue shimmer and Show a loss of viscosity (regarding macroemulsions). Did your emulsion Change from creamy white to clear bluish?
    I did a lot of research about microemulsions, but all testresults I had did not fit my aims:( I have the feeling this needs a lot of studying... All formula I created contained lots of surfactans, showed a higher viscosity with edges occuring when stored for 1month at RT. Also they were more Sticks Than light feeling (due to the higher amout of surfactants I think.)
    Maybe I should try your emulsifier?
    Do you have any tips for formulating microemulsions?
    Thanks a lot!
    Lara
  • edited February 4
    Yes Lara, the original formula used 50% of the amount of lipids but no silicone and was a medium-viscosity cream, quite suitable for a face cream but a little too thin for a hand cream.

    I was reading the bulletin for Silsense DW-18, a silicone ester that's water dispersible and acts as a co-emulsifier, and I noted the data on making a microemulsion with it.

    So, I doubled the amount of lipids and emulsifer thinking "this will be pretty damn thick" and added 0.7% of DW-18 and it came out as thin as water. It is still white though. This product would be useless in a traditional pot, would be ok as a sprayable. I'm not sure in which direction to go with it, I might progressively reduce the percentage of DW-18 and record how the viscosity changes.

    These silicone esters seem way different to traditional silicones. For instance I use a quarter percent of Polytrap in my hand cream and it produces a nice dry-but-silky effect. However, the DW-18 silicone ester appears to be absorbed by the skin, since even after quite aggressive hand washing, the silky feel of the silicone can be detected days later.

    I hope the above comments might be of use to you.
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • Hey Belassi,

    thank you so much for your answer!
    I did not knew, that there is a possibility to have a white microemulsion, as all the information I found said, microemulsions are translucent to clear due to the small droplet size.
    Earlier last year I also developed a sprayable emulsion that is very low viscous, but the technique of this i think was pit-emulsion, using very light feeling esters.

    I really think when I am back at work tomorrow I have to look up if we have some kind of silicone esters on stock! :-)

    For the thickening/stabilizing of your cream what do you think about adding low dosages of waxes like candelilla wax? Or adding an co-emulsifier like caprylyl glycol? As I am not so long working in the field of cosmetics I hope this is not a bullshit...

    For the way to go...once my boss said a good thing: There are no mistakes in development because there can always come out new ideas
  • I have been wondering about thickeners. Wax no, for two reasons; one, hard for me to obtain. Two, concern over propensity to cause acne. Probably a carbomer will work well. But first I will try to calibrate the effect of the silicone ester on viscosity versus percentage.
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • Ah, ok.
    I'm still not so much into the possible side effects like acne. Please let me know about the results. Im curious about it.
    In the meantime i think about thickeners i've already worked with. May be i can find something usefull.
  • edited February 5
    Thanks. 
    The formula is still a bit sticky which I don't like, despite eliminating the polysorbate-80.
    I think the mamey oil (little information available on this, it is a relative of Argan) contains a lot of unsaponifiables, which I suspect are glycerides. Therefore I think I will reduce the glycerine from 3% to 1% and increase water by 2%.
    Then I will make versions with 0.5%, 0.3%, 0.1% and 0% silicone ester, and see if I can make a viscosity curve.

    INGREDIENT~~~~~~~~~~OLD~~~~~NEW
    mamey oil ~~~~~~~~~~~~~5%~~~~~~5%
    cetearyl alcohol ~~~~~~~~~3%~~~~~~5%
    cetyl alcohol ~~~~~~~~~~~1%~~~~~~2%
    stearic acid ~~~~~~~~~~~~1%~~~~~~2%
    vitamin E ~~~~~~~~~~~~~0.5%~~~~0.5%
    Silsense DW18 ~~~~~~~~~0%~~~~~CALIBRATE
    fragrance 0.2%
    glycerol monostearate ~~~~~2%~~~~~2%

    The polar components include water at 78% glycerin at 1% and panthenol at 1%.


    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
  • edited February 5
    Anyone wanting to try their hand at this formula should be able to get pretty close by substituting Argan for Mamey. The missing % components are all actives (hydrosols).
    Special interests: anti-aging creams, gels, and serums; sulphate-free shampoos; and therapeutic cosmetics.
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