I recently attempted to formulate a lecithin microemulsion using 3.5g lecithin, 2.5g 1-butanol, 1.6g canola oil, and 1g PBS. The mixture appeared optically transparent.
I transferred the mixture into a test tube and centrifuged it at 2000 rcf for 15 minutes. After this, I noticed a very small cloudy layer at the bottom with a transparent layer on top that comprised most of the volume of the tube.
I extracted the transparent top layer and have been monitoring it. It has not shown any signs of cloudiness or separation over 24 hours. Nanoparticle Tracking Analysis shows the presence of nanoparticles in this layer; however, they have a broad polydispersity ranging from 10 - 400 nm (Mean: 196.3 nm Mode: 87.9 nm SD: 175.0 nm).
Given this information, is it possible that this clear layer contains microemulsion particles that simply need purification?
Raymond Doe
Your transparent layer contains microemulsion droplets, the sizes of which you yourself confirmed, but do not write what method. Then you want to clean them, but it is not clear why. The mixture you created is unique. If you change the concentration of one of the components, the droplet sizes will change. The distribution width may decrease, or it may increase.
Thank you for your response! Regarding what method I used, I used simple agitation method using a magnetic stir bar to homogenize the components while heating the mixture at 35-40 degrees C.
As to why I would clean them, I questioned if this sample was a true microemulsion because ideally truly stable microemulsions should not show any signs of separation post centrifugation (which this did). Microemulsions also concentrate in 10-100nm range and since the polydispersity of the top layer was broader, I questioned the need to clean them to remove any particles greater than that limit.
the centrifugation might have sedimented some salt resulting from PBS and/or lecithin. These salt precipitates can also result from mixing cationic and anionic surfactants together. If there is only a solid sediment, then you might have a microemulsion with some excess of salt, but if there is phase separation, then the initial dispersion was not a microemulsion. Phase separation could be better visualized with a different background of the photograph (e.g. some pattern like letters behind the sample for better visual inspection).
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