Other than constructing phase diagrams at different Surfactant:Cosurfactant ratios for different oil:surfactants ratios, is there a more scientific approach in predicting the optimal composition of a microemulsion?
The only idea that I have is to determine the optimal SF:CoSF ratio by determining the minimal interfacial tension between water phase and oil phase
The steps are:
1. Find the cmc, the partition coefficient and the adsorption isotherm of your surfactants (HFL is best for W|O, but nobody generalized it for mixtures)
2. Find the distribution between the two phases using equilibrium conditions and a mass balance. Depletion is important.
3. Define a stability condition as a function of surface coverage, charge or another
4. Optimize
You need also to insert a droplet radius in the calculation. You can either measure it or predict it through some model.
I did a similar thing for a project of mine, and I got beauuuutiful results. Unfortunately, BASF didn't continue the project. Hope I'll publish that some day.
...and HLB must be buried once and for all...
Measurment of OSMOTIC PRESSURE versus surfactant concentration.
You can use the hydrophilic/lipophilic difference (HLD) equation. Steven Abbot has a website with a good introduction to it: http://www.stevenabbott.co.uk/PracticalSurfactants/HLD.html
Edgar Acosta has published a number of papers on the approach, several in the AOCS Journal of Surfactants and Detergents. There is also a good introduction in the following paper: Journal of Colloid and Interface Science,Volume 325, Issue 1, 1 September 2008, Pages 259–266, "Hydrophilic–lipophilic deviation (HLD) method for characterizing conventional and extended surfactants," Witthayapanyanon, Harwell, Sabatini. Much superior to the old HLB method.
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