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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".
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