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O/W microemulsion stability questions
Good morning everyone,
I am formulating an aerosol air-freshener (pump spray) that needs to be clear at all compatibility conditions at room temperature, after 48 hr freezer and 110oF (43oC). It is a water base formula with buffered pH of ~5.0. I am using ~1.2% of fragrance oil. Due to VOC constraints (<3%) and other regulatory issues, I am trying to use at most 2% of ethanol as solvent (also as solubilizer). I have used successfully castor oil and another etholxylate surfactant blend to emulsify this system. However, in order to achieve clarity at all conditions, my surfactant blend total is up to 9% by weight of total formula.
Do you think this amount is too much? Do you foresee any problem with this formulation? How can I tell how much of surfactant is too much?
Another question I have is that for all clear formulations that I have created with fragrance oil, no matter the amount of total surfactant, ethanol and water base at different pHs, after the sample has been in the freezer for 24/48 hours they appear to be clear with no separation once they defrost. However, when I shake the container, I can see some “oily” but still clear looking swirls. I goes back to clear solution, but I wonder what is that? Has anyone observed this before? Can you explain this “phenomenon”? Should I be concern?
Thank you in advance
Ericka.
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3 Replies
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A problem? Yes, foam!. I have seen it in a few air fresheners. It was like a carnival. Honestly 9% seems like too much, what are you using?.
One solution would be a glycol as an antifoam agent, and it would probably help you with the low temps.
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For a microemulstion, the amount of surfactants is logical, but not commercially viable. So I would recommend you try other surfactant blends ( such as Tween/Span for different ratios). Another approach will be to soak the fragrance on fumed silica then dispersing it in water, it should give a relatively clear solution, though maybe a bit hazy.
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Thank you DAS and ChemicalPyros.
I appreciate your help.
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