Sunscreen Gel Formulation: Oil and Silicone Separation Issue
Question
I want to make a sunscreen gel similar to SpectraBan. I tried a formulation but after leaving it for 1 night, the oil and silicone separated.
I don't know what to add to emulsify/stabilize the oil + silicone phases.
The ingredients of SpectraBan are listed as:
- Cyclepentasiloxane
- Dimethicon Crosspolymer
- ETHYLHEXYL METHOXYCINNAMATE
- C12-15 alkyl benzoate
- Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine
- Cetyl Dimethicone
- Diethylamino Hydroxybenzoyl Hexyl Benzoate
- Cyclohexasiloxane
My attempted formulation is as follows:
Part A
- OMC 6%
- Octocrylene 4%
- lipid soft cc 5%
- DHHB 5%
- BEMT 3%
Part B
- Cyclomethicone 5%
- Silicone Gel thick&smooth qs. 100
Method:
- Heat Part A until dissolved.
- Add to Part B and blend.
The texture was good right after making it, smooth and nice to apply. However, after leaving it for 2 nights, the texture became sticky and separated, with oil clearly visible.
What can I add to make it stable?
Answer
Sunscreen Gel Stabilization
It appears the separation in your sunscreen gel formulation is due to the immiscibility of the oil phase (sunscreen actives, LipidSoft CC) and the silicone phase (Cyclomethicone, Silicone Gel Thick & Smooth). While the mixture looked good initially after mixing, over time the two phases separated because there isn't an ingredient to keep them stably blended together.
To stabilize your formulation and prevent this separation, you need to add an ingredient that can effectively blend and stabilize oil and silicone mixtures. Based on the product information, the following ingredients are suitable:
- Oil-Fix™ W (Silica Dimethyl Silylate): This ingredient is designed to increase the stability of water-in-oil or water-in-silicone formulas and can thicken various oils or silicones. It helps prevent formula separation and is suitable for formulations containing oil, silicone, or hydrocarbons.
- Oil-Fix™ S (Silica Dimethyl Silylate): Similar to Oil-Fix W, this is designed as a thickening/gelling agent in silicone or mineral oil and acts as a stabilizer in water-in-oil formulations by stabilizing the external oil phase. It is also suitable for formulations containing oils, silicones, or hydrocarbons.
Both Oil-Fix W and Oil-Fix S are types of Silica Dimethyl Silylate that can help create a stable gel texture by thickening the oil and silicone phases and preventing them from separating. You would typically add a small percentage (check product usage recommendations for the exact amount) of either of these ingredients to your formulation and ensure it is well dispersed.
Another option for blending oils and silicones is Oil Blender™ (Polyglyceryl-3 Diisostearate). While primarily a water-in-oil emulsifier, it is also designed to blend various oils and silicones and could potentially help improve the compatibility of your oil and silicone phases.
Adding one of these ingredients should help create a stable, homogenous sunscreen gel that does not separate over time.
