I am trying to create a water in oil macroemulsion with droplet sizes as large as possible (hoping to get between 0.1-1mm). I have no idea what surfactant to use or the volume of each phase to use.
I am using a homogenizer to do this, with either mechanical disruption or low-frequency ultrasound to create the emulsion. Any suggestions of parameters for this would be welcome also. The only confirmed parameter I have at the moment is a temperature of 37 degrees.
Many thanks
To select a surfactant, it is necessary to know the emulsion stability factor or the lifetime of the system, the hydrophilic-lipophilic balance, the geometry of the molecule, which maximum surface can stabilize the surfactant at a certain concentration, the distribution coefficient between phases, in which concentration limits the surfactant is a stabilizer of disperse systems. These are the key words (terms) with which you must become familiar in order to select a surfactant. Start with emulsion type, HLB, molecule geometry.
You have to make some choices. Settle first on droplet size - this choice will set surface area (interfacial area) to water volume ratio. Let’s say 500 um or 0.5 mm. The simple equation 6/6/d
...simple equation 6/d, or 120/cm. Assuming a density of 1 g/cm^3 for water, dividing this ratio by this density tells one that you will need to stabilize 120 cm^2/g of water. When you decide how much water you want to disperse, you can quickly calculate how much interfacial area must be stabilized. For such large droplets, surfactant or stabilizer choices will not be super critical, but a simple choice is to use Aerosol-OT, and assume it has an interfacial area of about 80 square Angstroms per molecule. I will leave it to you to do the rest. Use an oil phase that is not too toxic, but it is difficult to advise you further since you have not hinted about what you want to do with your emulsion. You can probably get by with a very highspeed blade type disperser, but homogenization will work. Make sure you give your emulsion time to "grow" to your target droplet size. Stir it overnight after homogenizing to allow coalescence to occur. Once your emulsion drops get close to your aim size, the coalescence will slow dramatically. Come back if you have more detail you can share. Good luck!
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