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TEWL ratings for Fatty Alcohols….Carbon chain length? Branched vs straight?
Because of my crazy personality….I have to turn over every stone on every ingredient. I create TEWL in my products from every possible angle. So today I would like to spotlight the fatty alcohol/s I might use in an upcoming project.
Typically I have on hand, Cetyl, Cetyl Esters, MM, and have just added Behenyl.
Is there a direct correlation between TEWL and say the carbon chain length…meaning Behenyl (longer) might be better or worse than say Myristyl (shorter)?
Do some charts exist that show TEWL ratings of a set vehicle, exchanging the different fatty alcohols?
I would like for my choice to retain the ability to thicken…but I can certainly adjust their inclusion rate….as I do when I select between say Cetyl and Cetyl Esters.
How would Octadecenol/Oleyl alcohol fit into the mix (new to me).
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4 Replies
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There is no definite answer because TEWL reduction not just depends on the chemical property of a given ingredient but also the supramolecular structure of the final product. Meaning, a micrometer droplet-type emulsion will be different from a sub-micron emulsion or a lamellar type.As a rule of thumbs, the higher lipophilicity is, the less interaction with water molecules and hence a lower TEWL. Lipophilicity correlates with longer chains, by tendency also branching, and the absence of a free alcohol function. Cetyl alcohol has likely a poorer effect on TEWL reduction than cetyl ester, behenyl alcohol is better than cetyl alcohol and that one is better than myristyl alcohol. Cetyl esters… well… depends what type of ester it is… likely better than myristyl myristate. Oleyl has a double bond… my gut feeling tells me that it could be superior to the equally long stearyl alcohol though said double bond will have a considerable effect on structure and how that different structure affects TEWL???? -
you may use this silicone. Very close to petrolatum for TEWL but 20 times more expensive. -
Abdullah said:you may use this silicone. Very close to petrolatum for TEWL but 20 times more expensive.
That graph shows that common dimethicones (350 cst, and surely the 1000 cst as well) are way more permeable than petrolatum. Increasing the chain lenght of the alkyl group in an alkyl modified silicone decreases permeability for sure, but in the practice, I haven’t seen a higher chain lenght than C16 (cetyl dimethicone), which is still somehow permeable.
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ketchito said:Abdullah said:you may use this silicone. Very close to petrolatum for TEWL but 20 times more expensive.
That graph shows that common dimethicones (350 cst, and surely the 1000 cst as well) are way more permeable than petrolatum. Increasing the chain lenght of the alkyl group in an alkyl modified silicone decreases permeability for sure, but in the practice, I haven’t seen a higher chain lenght than C16 (cetyl dimethicone), which is still somehow permeable.
SiCare 264-70 is C30-45 Alkyl Dimethicone.
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