I prepared O/W macroemulsion and studied for one month storage at three different conditions (4, 25 and 40 deg C). At the end (on 30 th day), I found slight creamy layer and checked for droplet size. Fresh emulsion is 1.3 um, after 30 days at 40 deg it is 0.5 um, for 25 deg it is 1.0 um and 4 deg it is 1.2 um.
How it is possible? What would be the mechanism behind that? Mechanisms like creaming/sedimentation, flocculation, and coalescence would increase the droplet size..
The macro-emulsions (in your case O/W emulsions) are not thermodynamically stable and as a results the droplet size would vary overtime. Usually if you track the droplet size distribution with time they will become larger to reduce the overall contact area with surrounding fluid
Mahdi,
Thanks for the immediate reply. I check at 15th day and on 30th day. Gradual decrease in droplet size is there. Mean droplet size at 15th day and 30th day for different conditions is in the attached file.
D'Souza,
The way that you take sample to run your size distribution analysis is very crucial. If you have creaming or sedimentation over time that by itself means that your larger droplets have already coagulate and you have to take this fact into consideration. If you have a bottle, I recommend take three samples from top, middle and the bottom and then run size distribution for each sample separately.
Mechanism of creaming/sedimentation does not change the overall size distribution, it changes only the local distribution.
You have run in a basic problem of sampling, which is not only the need of sampling at different locations. You cannot avoid fully loss of part of the original droplets if coalescence proceeds. The larger the droplets the easier will be coalescence. Eventually droplets will grow above the point where you can get them into a representative sample. Even worse, you cannot account for the oil film on top and on the walls of your container. Therefore you found the reasonable correlation - the less stable the emulsion during storage conditions the more you lose the larger droplets. Reducing time of storage sufficiently you may find the other expected result.
Dear Titus Titus Sobisch
Could you suggest some paper about the droplets size changes during storage?
best regards
Maciej
any book on emulsion science will serve this.
you may look also e.g. into Chapter Evaluation of Long Term Stability of Model Emulsions by Mult...
Thanks a lot Titus.
I would like to cite this in my next paper :)
It was pleasure for me to read your answers about emulsions systems and so on
All the best
Maciej
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