Scans in general
Here are 4 proven methods for measuring EACN, with 3 of the methods showing you what to expect in your test tubes. You can use the apps to plan your tests, then to analyse them. These aren't just pretty pictures - these are formulation tools that I and many others use on a regular basis.
There are 3+1 types of EACN scan. Each type has its own good and bad aspects - and one key aim of this page is to allow you to choose the best scan for your particular circumstances. The +1 is a very different type of scan, discussed after the 3. But whatever the scan, the starting point is a 50:50 v/v O/W mix with, typically 3-6% of surfactant. Select whether the surfactant type is ionic or non-ionic, the number of tubes (from 5 to 16) and your known values such as surfactant Cc or salinity (range). Temperature is assumed to be 25°C. As you change the EACN of the oil with the slider you get a simple visual idea of what the scan tubes might look like if your unknown oil had that EACN. Below each tube is key information of what is going on. To interpret a real scan, move the EACN input so the tubes match the scan. That EACN value is the value for your unknown oil. Real tubes can often look rather different, but by comparing your real scan results to this idealised picture you will be able to pin down the EACN to the accuracy set by the limits of your scan.
Note that with the wrong choice of input values it is possible that you will see no change across the whole scan range. When this happens (in real life and in the simulation), the trick is to see if the tubes have a larger water phase (meaning that some of the oil is in the water) or larger oil phase (meaning that some of the water is in the oil) and therefore knowing in which direction the known surfactants have to be shifted.
It is assumed that you have a set of surfactants with known Cc values and, for one of the scans, you must have an oil of known EACN value
The phases in the scans are shown in orange for oil, sky blue for water, pink for the mixed phase.
In each case the %Surf value is meant to illustrate the fact that more surfactant gives more solubility and therefore bigger differences between the phases. The value varies from 1 to 10 for convenience and the effect is exaggerated.
Measuring EACN with 2 known surfactants
Choose the Cc and MWt of your two surfactants and your salinity. As the Cc tutorial explains, the MWt is required because the Cc of a mix of surfactants depends both on the relative wt% and the MWt, a smaller MWt representing a bigger contribution for a given wt%.
Measuring EACN with known Cc and known EACN
An alternative is to choose a known surfactant and a known EACN and scan the mix of the two EACNs. Because the effect of EACN on HLD is governed by the factor of 0.17, it is not a very accurate method, but it can be excellent for pinning down an EACN before using a more accurate scan to get an exact number. The MWt of the surfactant has a small effect on the "salt correction factor" where ionic surfactants add to the overall salinity by 0.3*%Surf*58/MWt.
Measuring EACN with known Cc and Salt scan
A third method is to choose a known surfactant and to vary the salinity. If the surfactant can survive high salinities then this can be an excellent, accurate way (often used by academics) to pin down an EACN. The values of S-min and S-Max set the range of the scan. The MWt of the surfactant has a small effect on the "salt correction factor" where ionic surfactants add to the overall salinity by 0.3*%Surf*58/MWt.
The PIT-shift method
Because the PIT (Phase Inversion Temperature) of ethoxylate systems can be measured accurately and shifts strongly with EACN there is a fine tradition of measuring EACNs via the PIT. See, for example, the work of the Aubry group in Lille1. Such a technique works well for standard oils within a modest EACN range but could not, for obvious reasons, give the EACN of, say, dodecanol. A paper by Tchakalova at Firmenich2 provides a very smart way to measure EACNs over a very wide range of values - down to -28 for dodecanol! The trick is to find an ethoyxlate surfactant (e.g. C10EO5) and an oil (IPM, EACN=7) and a convenient PIT (40°C). By measuring the PIT for some standard oils (hexane to hexadecane) it is possible to obtain a linear calibration curve of PIT v EACN. Finally, add a small % (in the paper this is 6.5 wt% with respect to IPM or 3% of the total formulation) of the test oil and measure the PIT. From the calibration curve you now know the EACNmix and from this it is possible to calculate the EACN of the pure oil from:
where x is the mole fraction of the reference oil (in this case IPM) or the oil. This mole fraction rule seems to work better than the vol% rule used elsewhere in Practical Surfactants.
The inputs are straightforward except for α. This is the temperature dependence of PIT on EACN: PIT=PITref+(EACN-EACNref)/α. Given the standard HLD T-dependence for ethoxylates of 0.06 and the EACN dependence of 0.17, α should be ~0.06/0.17=0.35 and in the paper it is found to be 0.32.
PIT Shift Method
How accurate is this method? The answer is "accurate enough for most purposes". If you need an accurate EACN of a pure oil in the 3-16 range then it's probably better to measure the PIT using the pure oil. But if you want to know lots of EACN values spanning a wide range then this method excels. The paper, for example, covers fragrances . The EACN of limonene is notorious for being highly variable, presumably because most "limonenes" are not chemically pure, they are simply "good enough for a fragrance", and some fragrance components are themselves mixtures of components which will vary from batch to batch. And, of course, you cannot actually measure an EACN of -28 for dodecanol using the classic technique. Whether it is -29 or -27 is not really important, but the fact that it is not -15 or -5 is important.
1S. Queste, J.L. Salager, R. Strey, J.M. Aubry, The EACN scale for oil classification revisited thanks to fish diagrams, Journal of Colloid and Interface Science 312 (2007) 98–107
2Vera Tchakalova and Wolfgang Fieberm, Classification of Fragrances and Fragrance Mixtures Based on Interfacial Solubilization, J Surfact. Deterg. (2012) 15:167–177