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Esters, Polarity, Compatibility, Miscibility
Hi everyone,
I’m a bit confused by polarity/compatibility/miscibility
I am going with the rule of thumb that polar mixes with polar and non polar mixes with non polar (unless aided by emulsifiers etc)
Since our hydrocarbons (squalene, hemisqualane and their friends) are non polar, does that mean they can’t mix with polar esters (simple, myrystyl myristate, isoamyl & isopropyl esters, guerbet, coco caprylate etc)?
I know that triglycerides are polar, but plant oils as a whole are non polar, so how come plant oils mix with polar esters?
Thank you
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3 Replies
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@Anca_Formulator really interesting question what I can tell you that it is not a rule that the miscibility of two ingredients impose that they have same polarity as example alcohol is miscibile with different polarity… Really interesting to hear more from experts about subject.
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The use of the expression ‘polarity’ is not super accurate and very cosmetic because cosmetic isn’t an exact science and often performed by people without or minimal education in natural science; it would be useless for most manufacturers if raw ingredient companies indicated Hansen solubility parameters and the like… pretty much the same reason why HLB is still in use and not HLD-NAC.From a chemical point of view, triglycerides are esters (one glycerol and three fatty acids) as much as ester oils (aka liquid wax, one fatty acid with one fatty alcohol). Hydrocarbons don’t have heteroatoms and are therefore more lipophilic (and have no polarity) whilst silicone oils (standard dimethicone, not modified ones) are even more lipophilic with equally absent polarity. ‘True’ polarity comes with alcohols (such as your mentioned Guerbet alcohol) and amines and other electron donating and withrawing heteroatoms. True, esters and amides impart that too but the effect is marginal, non-miscibility comes rather from other solubility parameters than ‘polarity’. There’s also a difference between miscibility and solubility. As a rule of thumbs, equal mixes with equal. ‘Polarity’ in the way you refer to it does rather affect emulsion type (lyotropic liquid crystalline phases) or, in common cosmetic language, HLB requirement (or apparent HLB values). -
@Pharma: Thank you so much for a great explanation.
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