1. So you want to make an emulsion…
A simple guide to HLD-NAC by
Professor Steven Abbott

2. Formulating blind There are 1000’s of surfactants to choose from
If you are lucky the suppliers will reveal an HLB or CMC value and if you’re very clever you might be able to calculate a CPP (Critical Packing Parameter) for the surfactant
But none of the data will tell you if this surfactant works for this oil at this temperature and this salinity
Even if it did it wouldn’t tell you how efficient the surfactant might be

3. Types I, II and III
Sometimes you want an oil-in-water (o/w) microemulsion, a Winsor Type I
Sometimes you want a water-in-oil (w/o) microemulsion, a Winsor Type II
Sometimes you want a crystal-clear w-o blend, a Winsor Type III
And even if you don’t want a microemulsion, you probably want to know if you have an efficient surfactant for o/w or w/o

4. HLD
Hydrophilic Lipophilic Difference allows you to calculate the optimal surfactancy for a given system
HLD = A*Salinity + B*Temperature + C*EACN + Cc
You know your required salinity and temperature, you might know the Effective Alkane Carbon Number (EACN) of your oil, so if you know the Characteristic Curvature (Cc) of your surfactant you can calculate HLD
The real HLD formulae look a little different, this simplistic version is to make a point about EACN and Cc

5. HLD=0 When HLD=0 you have optimal surfactancy:
Lowest interfacial tension
Highest solubility of oil-in-water and water-in-oil
When HLD is very large (negative or positive) you are very far from optimal and your formulations will be poor
When HLD is small and negative you have great o/w microemulsions
When HLD is small and positive you have great w/o microemulsions
And if you have great microemulsions, the chances are that the surfactant is right for normal emulsions of the same oil

6. EACN Hexane =6, Decane = 10 etc.
Experimentally, Toluene behaves like an alkane with 1 carbon (EACN=1), Isopropyl Myristate behaves like an alkane with 13 carbons (EACN=13)
If you know your EACN you are close to finding the optimal surfactant

7. Cc
These values are known for ~30 common surfactants such as CxEOy, SLS, AOT, Lecithin …
Cc values of mixtures are the average of the individual Cc values, so you can fine-tune Cc
A good start, but not enough!

8. Phase scans
Take 10 vials and shake up your oil and surfactant with water of a range of salinities
Or take your water and surfactant and shake them with a range of EACNs
If you’re in the right formulation space, the emulsions will pass from o/w through optimal Type III to w/o
The S* (optimal salinity) or EACN* (optimal oil) then lets you calculate Cc for the surfactant

9. High Throughput
With a robot you can do hundreds of scans and get good data on surfactant Cc values or, using known surfactants, EACN values of unknown oils (e.g. perfumes)
If we had large datasets of Cc values and oils we could all formulate much more effectively
The Intelligent Formulation “green surfactant” project is a first step towards a larger database of Cc values

10. NAC
HLD tells you when you are in the right area for a surfactant, but not how efficient it will be
The Net Average Curvature part of the theory tells you the efficiency of the surfactant*
A large “effective tail length”, l, and a large “chi parameter” gives you high efficiencies
l can be estimated reasonably
The phase volumes from the phase scans allow you to calculate chi
With Cc, EACN, l and chi you can formulate rationally
See the full HLD-NAC.pptx for an explanation of NAC

11. Simple theory but …
… it’s hard to keep track of what’s going on as temperatures, salinities, EACNs, chi values etc. are changed, especially with surfactant mixtures
So the Optimal Surfactant HLD-NAC software package does the calculations for you and shows what’s going on via calculated values and 2D and 3D plots
And it’s free software

12. What the software can do for you
If you have enough Cc, EACN and chi values it’s very easy to choose a surfactant (blend) that places you in the right part of surfactant space
From there it’s easy to fine-tune your formulation

13. What you can do for the software
The more Cc and chi values we have, the better we can all formulate
If you use the software to determine Cc and chi you can choose to keep those values for yourself
But if everyone does that, we’re all worse off
So why not share your values so that others will also do so?
The software makes it easy to add to the database so if we collate new values a new dataset can be sent out with each updated version of the software

14. Our dream
That Cc and chi will become the standard values provided by surfactant suppliers
So surfactant formulation becomes a science, not an art
That during the process of finding out these values, various issues/problems/defects of HLD-NAC theory get solved so the predictive power increases
So start the adventure at

15. Acknowledgements
HLD theory was developed over many years by (in alphabetical order) Profs Aubry, Sabatini and Salager
HLD-NAC theory was first developed by Prof Sabatini’s group in Oklahoma
It has been developed further by Prof Acosta at U. Toronto
The software package has been developed with the kind help of Prof Acosta