I am trying to make a dispersion for hydrophobic materials. Basically my material is a metal stearate. If I want to disperse it in water and make it stable, what are the criteria that we should look into? For eg. types of surfactant, ratio, HLB etc.? How should I start with?
Siti Shafiah Shazali
These metal stearates (e.g. Zn, Ca) are not easy to disperse especially if small and sticky. However, you just need almost any surfactant to get the material to wet in water. Try washing up liquid as an experiment, putting neat liquid into the stearate and 'spatulating' (mixing with a spatula) before adding to water with stirring. Note that foaming could be an issue especially if you want to measure the size distribution by laser diffraction. Sonication could aid the dispersion.
Other considerations:
- In a controlled or food/FDA application then one may consider a non-ionic surfactant e.g. Span, Tween, Nonidet
- Reduce the concentration of surfactant until it just wets the system and allows adequate dilution for the measurements you wish to carry out
Stability is a subjective word and depends on the application. At worst the system needs to be stable for the duration of the measurement regime.
Alan F Rawle Thank you for your explanation. May I know how to calculate the HLB value for the mentioned sample in order to find the right surfactant?
Siti Shafiah Shazali
The right surfactant is the one that works in a cost-effective manner.
Google is your friend:
https://en.wikipedia.org/wiki/Hydrophilic-lipophilic_balance
This approach is too theoretical, IMHO. Nothing better than a few experiments - start with washing up liquid and see how you go. This is something where empirical chemistry will have quicker results.
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