Emulsifier Recommendation for Unstable Serum (Soy Lecithin + Tween 20)

Hello,

It sounds like you're experiencing instability with your serum formulation using Soy Lecithin and Polysorbate 20 (Tween 20) at an estimated HLB of 6-7. This can happen because Soy Lecithin is often a weak emulsifier on its own and requires co-emulsifiers or stabilizers, especially in low-viscosity serum formulations. While combining it with Polysorbate 20 helps adjust the HLB, the resulting system might still lack the necessary stability for your specific oil phase and overall formula composition. An HLB of 6-7 is typically suited for W/O (Water-in-Oil) emulsions, but for a serum, an O/W (Oil-in-Water) emulsion is more common, which usually requires a higher HLB. If you are aiming for an O/W serum, the HLB might be too low, or the emulsifier system isn't strong enough.

To improve stability, you could consider adding a co-emulsifier or using a more robust primary emulsifier designed for serums. Here are a couple of options that could help:

• PhosphoMax™ (Natural Phospholipid Emulsifier): This is a natural emulsifier with an approximate HLB of 10, suitable for O/W emulsions. It can effectively emulsify up to 20% oil and also acts as a penetration enhancer. When using PhosphoMax™ as the primary emulsifier, it is highly recommended to use it in conjunction with a thickener like Xanthan Gum (at least 0.3%) to provide additional stability to the emulsion, which is particularly helpful for low-viscosity serum formulas.
• SoftGel 305 (Polyquaternium-37 Based Emulsifier): This is a synthetic, easy-to-use, heat-free emulsifier and thickener. It can emulsify up to 5% oil and works over a wide pH range (3-11). SoftGel 305 is excellent for creating serums or light creams and provides a pleasant soft feel on the skin. Its thickening property also contributes to emulsion stability.

Choosing between these depends on your preference for natural ingredients and the desired feel and oil percentage in your serum. PhosphoMax™ offers a natural option and higher oil load capacity but requires a thickener like Xanthan Gum for stability. SoftGel 305 is a convenient synthetic option that acts as both emulsifier and thickener for lower oil percentages.

You could also explore using a small amount of a gel-forming thickener like Carbomer U21 in addition to your current emulsifier system or a new one. While not a primary emulsifier, Carbomer U21 can significantly improve the stability of emulsions by increasing the viscosity of the water phase and preventing oil droplets from coalescing.

Consider the percentage and type of oils in your formula, as this greatly influences the required HLB and emulsifier choice. Experimenting with different emulsifiers and potentially incorporating a thickener should help you achieve a stable serum.