I am screening some essential oils such as Manuka, Myrtus, Melissa, Eugenol, TTO ecc.. at concentrations ranging from 0% to 8%. I am using Tween 80 to enhance the solubilization of the oil in the media. I read that the normal concentrations of tween 80 used are around 0.5% (v/v) but even increasing the concentration at 4% (v/v) I am not able to obtain a well mixed suspension.
I add the tween 80 to the media, stirring for 1 hours and after I add the oil.
Am I doing anything wrong? Do you have any idea on why I am not able to mix the oil using the concentrations found in literature? Should I use other surfactants?
Thank you very much for your help.
Best wishes,
Elisa Serra
Dear Elisa,
As you mentioned that tween 80 used in concentrations up to 0.5%. Increasing its concentration is not going to make any good. To my knowledge Tween 20 is a better emulcifying agent than tween 80.
The following agents are used as emulsifiers in pharmacy:
emulsifying wax, cetearyl alcohol, polysorbate 20, and ceteareth 20.
Sometimes in order to obtain the adequate HLB for the emulsion two emulsifying agents are used.
Therefore, I suggest to replace tween 80 with one or more of the above mentioned emulsifiers.
Herein a general procedure for making emulsions:
General Procedure:
Blend the oil and surfactant together in a vessel suitable for emulsification. The required amount of water is then slowly added to the oil phase with a constant rate of agitation. The emulsion may become viscous with the initial addition of water, but a sharp decrease in viscosity will occur upon the addition of more water. This is the inversion point at which the emulsion changes from a water-in-oil to an oil-in-water emulsion. After the emulsion reaches the inversion point, the remainder of the water may be added quickly. Agitation should be continued until the emulsion reaches ambient temperature without forced cooling.
In emulsion preparation, a series of trials are performed to select a proper surfactant system. Each surfactant has a specific HLB (hydrophile-lipophile balance) number. Likewise, each oil has a "required HLB." If the required HLB for an oil is known, select surfactants or surfactant blends with HLB numbers close to the required HLB number. A number of different surfactants with the required HLB number should be examined. Not all surfactants having the same HLB value will be acceptable.
When the HLB value for the ingredient(s) to be emulsified is unknown, the following procedure can be used. Two surfactants with different HLB values are selected -- usually one is oil soluble, the other is water soluble. Blends of these surfactants in different proportions are prepared. These surfactant blends are then mixed with the ingredient(s) that need to be emulsified. If all emulsions appear to be initially acceptable, this means that the amount of surfactant or surfactant blend added is in excess. Trials should then be repeated with smaller amounts of the surfactant or surfactant blend. If all emulsions appear unacceptable, a higher concentration of surfactant or surfactant blend should be tried. If an emulsion appears to be stable, then this system should be optimized and tested for long-term storage stability.
To increase the amount of oil in the emulsion, the surfactant concentration should be increased.
Generally 1-10% surfactant is used in most emulsion systems.
Surfactant blends generally provide better emulsification than individual surfactants.
The viscosity of a oil-in-water emulsion can be increased by increasing the level of oil. To reduce the viscosity of an oil-in-water emulsion, the amount of water should be increased.
Emulsification technique is very important in producing a stable emulsion. Some important factors to consider include emulsification temperature, type of mechanical agitation used and the order in which ingredients are added.
http://dowac.custhelp.com/app/answers/detail/a_id/1845/~/procedure-for-emulsification-of-oil-in-water-using-surfactants
Hoping this will be helpful,
Rafik
Dear Elisa,
As you mentioned that tween 80 used in concentrations up to 0.5%. Increasing its concentration is not going to make any good. To my knowledge Tween 20 is a better emulcifying agent than tween 80.
The following agents are used as emulsifiers in pharmacy:
emulsifying wax, cetearyl alcohol, polysorbate 20, and ceteareth 20.
Sometimes in order to obtain the adequate HLB for the emulsion two emulsifying agents are used.
Therefore, I suggest to replace tween 80 with one or more of the above mentioned emulsifiers.
Herein a general procedure for making emulsions:
General Procedure:
Blend the oil and surfactant together in a vessel suitable for emulsification. The required amount of water is then slowly added to the oil phase with a constant rate of agitation. The emulsion may become viscous with the initial addition of water, but a sharp decrease in viscosity will occur upon the addition of more water. This is the inversion point at which the emulsion changes from a water-in-oil to an oil-in-water emulsion. After the emulsion reaches the inversion point, the remainder of the water may be added quickly. Agitation should be continued until the emulsion reaches ambient temperature without forced cooling.
In emulsion preparation, a series of trials are performed to select a proper surfactant system. Each surfactant has a specific HLB (hydrophile-lipophile balance) number. Likewise, each oil has a "required HLB." If the required HLB for an oil is known, select surfactants or surfactant blends with HLB numbers close to the required HLB number. A number of different surfactants with the required HLB number should be examined. Not all surfactants having the same HLB value will be acceptable.
When the HLB value for the ingredient(s) to be emulsified is unknown, the following procedure can be used. Two surfactants with different HLB values are selected -- usually one is oil soluble, the other is water soluble. Blends of these surfactants in different proportions are prepared. These surfactant blends are then mixed with the ingredient(s) that need to be emulsified. If all emulsions appear to be initially acceptable, this means that the amount of surfactant or surfactant blend added is in excess. Trials should then be repeated with smaller amounts of the surfactant or surfactant blend. If all emulsions appear unacceptable, a higher concentration of surfactant or surfactant blend should be tried. If an emulsion appears to be stable, then this system should be optimized and tested for long-term storage stability.
To increase the amount of oil in the emulsion, the surfactant concentration should be increased.
Generally 1-10% surfactant is used in most emulsion systems.
Surfactant blends generally provide better emulsification than individual surfactants.
The viscosity of a oil-in-water emulsion can be increased by increasing the level of oil. To reduce the viscosity of an oil-in-water emulsion, the amount of water should be increased.
Emulsification technique is very important in producing a stable emulsion. Some important factors to consider include emulsification temperature, type of mechanical agitation used and the order in which ingredients are added.
http://dowac.custhelp.com/app/answers/detail/a_id/1845/~/procedure-for-emulsification-of-oil-in-water-using-surfactants
Hoping this will be helpful,
Rafik
Dear Rafik Karaman,
thank you for your answer and the protocol that you sent me.
it helped me a lot.
Kind regards,
Elisa
In addition to what Rafik had said, a mixture of tween and span usually offer more pleasing outcome than tween alone.
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