So you want to make an
emulsion…
A simple guide to HLD-NAC by
Professor Steven Abbott
www.stevenabbott.co.uk
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
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
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
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
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
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!
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
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
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
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
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
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
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 HLDNAC theory get solved so the predictive power
increases
• So start the adventure at
www.stevenabbott.co.uk/HLD-NAC.html
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