Practical Surfactants is a set of web pages and apps created on the basis of the HLD-NAC approach of Prof Edgar Acosta of U. Toronto. With the input from other surfactant experts it is expanding to encompass more and more of the issues that face formulators from day to day.
Its aim is to allow those who aren't necessarily great experts on surfactants to be able to design (micro)emulsions quickly and efficiently. Unlike HLB, CPP etc. HLD-NAC actually works for a wide range of oils and surfactants.
There is a some explanation below of HLD-NAC along with some older resources which are still useful. But the PracticalX series in AbbottApps is where the future lies. It includes Practical Foams and Practical Hydrotropes as well as areas not connected to surfactancy.
For non-experts, rationally designing microemulsions is very hard. Although there are many excellent papers on the theory of microemulsions it is hard to know exactly what would happen if you used this surfactant at that concentration at that salinity at that temperature with that oil. HLB, CPP and many other tools just aren't useful for such purposes.
The work over many years by (in alphabetical order) Prof Aubry, Prof Sabatini and Prof Salager has created the highly useful concept of HLD - Hydrophilic Lipophilic Difference. With a few key parameters it is easy to find the conditions (salinity, temperature, oil) which would produce the minimum interfacial tension and the highest solubilisation of water in oil or oil in water. Building on HLD theory, Prof Edgar Acosta at U. Toronto (with his co-workers) has developed the NAC, Net Average Curvature extension to HLD theory so that many more details of a microemulsion can be modelled.
The bottom line for practical surfactant formulators is that if you know the EACN (Effective Alkane Carbon Number) of your oil and the Cc (Characteristic curvature) of your surfactant then you already know how close you are to an optimal surfactant (maximum surfactancy for minimum surfactant). This is the HLD part. If you know the extended chain length, head area and "chi parameter" of your surfactant then the NAC part tells you how efficient your surfactant will be - getting the best emulsion for the least surfactant. If you have the key parameters for a range of surfactants then you can make a rational choice of surfactant (or surfactant blend) to get you started in your formulation optimization process.
What about "real" emulsion?
The theory is designed for microemulsions, the thermodynamically stable, clear emulsions that are of increasing interest in perfumes, cosmetics, and pharmaceuticals as well as in the field of extended oil recovery for which much of this theory was developed. However, there is strong evidence linking the understanding of microemulsions to that of real emulsions. The most basic fact is that emulsions are less stable when they are far from the best locations for o/w and w/o microemulsions, and are highly unstable at the optimal surfactant sweet spot. So the curves within the HLD-NAC software are exact predictors of general emulsion stability. There is much more to be said on this subject and a document will be posted here sometime in the near future.
What about the Optimal Surfactant software package?
Although HLD and HLD-NAC are relatively simple theories, they are hard for non-experts to grasp in full. I (a non-expert) therefore wrote, at first for my own use, a user-friendly software implementation of HLD-NAC theory. Using it I was able to formulate right-first-time w/o and o/w microemulsions with difficult cosmetic oils. Since that early crude version I have worked with Prof Acosta on improving the software and also extending the database of key surfactant parameters including some of the latest extended surfactants. The software has now been used on several microemulsion formulation projects and has proven to be very useful in the hands of non-experts. As word has spread through the surfactant community there have been more requests for access to the HLD-NAC Optimal Surfactant software. The package of software, data and explanation has been offered, free of charge, to the surfactant community. But because it is restricted to Windows machine, and because all updates to the theory are contained within Practical Surfactants, it remains on this page for those who might still find it useful but will not be further updated.
Access to the package
To explore HLD-NAC the minimum requirement is to download Optimal_Surfactant.zip which you simply unzip into a convenient folder to be up and running - provided that the Microsoft DotNet Framework 4.x (freely available from Microsoft) is installed on your PC. More information about installation and PC requirements, plus legal disclaimers etc. is available in HLD-NAC_Software_Installation_and_use.doc. The Help file provided with the package contains a simple explanation of HLD-NAC theory and can be downloaded as Optimal_Surfactant_Help.rtf. A short document describing three different examples of the software in action (using parameter files provided with the software) can be downloaded from HLD-NAC_Working_Examples.doc
The core set of HLD-NAC papers for those who want to get into the theory is available as Core_Optimal_Surfactant_Papers.zip
A very simple Powerpoint description of HLD-NAC can be downloaded as Simple_HLD-NAC.ppt.
My personal view of HLD-NAC theory in comparison with other theories is available as a Powerpoint Presentation, HLD-NAC.ppt. I would positively welcome criticism and suggestions for improvements to this document.
Problems and possibilities
HLD-NAC is an imperfect theory. The update to Practical Surfactants released on 1 Sep 2013 has supplied some significant advances from Prof Acosta and now there is a critical mass of other researchers advancing this sort of approach. There are plenty of other ideas (some, like CIT, included in Practical Surfactants) that complement HLD-NAC and the aim now is not to fight between the ideas but to find the synergies which will create a more powerful framework for the future.
HLD-NAC in action
The theory is now being used extensively for "real world" work. VLCI in addition to offering a service for measuring HLD-NAC parameters is using the theory to solve clients' formulation problems in a number of areas. Several large corporations are also using the software for their own optimisations, and a number of universities are finding it a useful teaching and formulations tool. The software is being used for an important European O4S Organics For Surfactants project and the media page on that site shows me doing some measurements of Cc values of bio-surfactants produced at the Fraunhofer IGB in Stuttgart. It is also featured in my on-line 5-lecture series of Optimizing for Cosmetics for Cosmetics & Toiletries.
An independent view of the use of HLD-NAC theory in microemulsion formulation is covered in the chapter by Deeleep K. Rout et. al. in the excellent free book on Microemulsions edited by Reza Najjar Microemulsions - an introduction to properties and applications.
I would like to thank Profs Aubry (U. Lille), Sabatini (U. Oklahoma) and Salager (U. de Los Andes) who were most generous in their answers to my queries about their work on HLD.
I would especially like to acknowledge the wise and helpful input from
Prof Acosta U. Toronto (right) and thank him for his encouragement and support for the HLD-NAC project and for the most recent updates to Practical Surfactants.
Please send all feedback/comments on the HLD-NAC package to me at