The Stability And Characterization of Colloidal Dispersions (Emulsions, Suspensions) - Measuring Directly

You have two choices to measure the stability of your colloidal dispersion (ISO Technical paper 13097):

1.   The direct method

2.   Correlative methods (indirect)

The direct method is a first principle method. The indirect method is not.

Correlative or indirect methods are analytical techniques such as particle sizing, rheology, zeta potential, and surface tension.

Indirect methods rely on complex theories or black-box algorithms to infer stability. There is nothing wrong with indirect methods, but they cannot give you definitive stability results.

On the other hand, direct methods give you unambiguous emulsion and suspension stability answers and results.

The direct method bases its results on observing and measuring stability directly. There is no derivation from a higher principle.

By measuring directly, you are capturing the cumulative effect of particle size, the density difference between the dispersed and continuous phase, viscosity, and interfacial or surface properties.

Let me give you a very simple example. Imagine you just created a product made up of a dispersed phase (droplets or particles), dispersants (surfactants or emulsifiers), and a viscosity modifier (thickener).

And now you want to know how stable your product is at that time point.

The traditional route (indirect method) first dilutes the sample to measure particle size and zeta potential (or interfacial tensions). After that, perform rheological measurements on the undiluted product. Then put everything together on a spreadsheet and try to determine the product stability.

Or you can choose the direct method and obtain the product stability in one measurement. And do so without having to dilute your dispersion.

That is the advantage of measuring dispersion stability directly. It is fast, simple, and accurate.

The three primary direct methods used for emulsion and suspension stability analysis are

- the human eye

- Formulaction’s Turbiscan

- LUM’s STEP-Technology®

For more information, please go to www.iso.org.