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Octadecane O/W emulsion
Hello everyone,
I’m in a tough spot. I’m trying to synthesis a stable phase changing emulsion, meaning it goes through thermal cycles (tempering).
The oil is n-octadecane and the water is the continuous phase.I using span 60 and tween 60 as the surfactants I’m utilizing the HLB method to match the surfactant ratio to the HLB of the oil which isn’t really known.
I have tried HLB 10, 11,12 with different weight percentages of the surfactants (3,5,7,9).
Seems that obviously the more surfactant the longer it takes to phase separate. However, the lower the HLB the more stable the emulsion. These were stored at 60degC.
I’m curious about adding an anionic surfactant to help better stablize the emulsion due to electrostatic repulsion. Which one should I utilize, sodium stearate?
Also, what are good method in synthesizing nanoemulsions other than Phase inversion method?
Thanks
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7 Replies
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Phase inversion in case of different Tweens is highly temperature but also HLB and oil-phase dependent. Some literature HERE as an example of PIT.
If I read Figure 8 right, Tween 60 in hexadecane has a PIT of slightly above 100°C. Once you change things, say by adding a Span, PIT changes. You sure that 60°C is the right temperature and why do you store your phases/emulsion (?) at 60°C?Do you use some kind of measurement to determine the right amounts/proportions (of everything) as well as droplet size and size distribution?On the other hand, you could also use the PIC approach (which is obviously suitable for non-PEG based surfactants which don’t have a PIT but also works with PEG based surfactants). Another version is D-phase emulsification, ultrasound, or very high speed/shear mixing.You might get more hits searching for hexadecane
. Octadecane should have a similar HLB requirement, probably a fraction of a unit higher?Found a publication on hexadecane wherein they investigated different Tweens and Spans at HLB 11.8 and only mixtures containing either Tween 80 or Span 80 or both at a 7:3 ratio (to yield HLB 11.
gave stable emulsions of about equal hexadecane and emulsifier %.BTW a standard anionic surfactant would be sodium lauryl (but also laureth) sulfate at 1-10% relative to the total amount of surfactants used. Glyceryl stearate citrate or nearly any other could also be used. -
I’m storing it at 60degC to promote separation. It’s stable at room temperature to about 50 degC. I’m not sure if the Span 60 is the reason for this. It’s melting temperature is around 55 degC. So I’m thinking that Span 60 is making a crystalline network which is prohibiting the droplets to move.
Any idea what I should do to verify that?
I am using DLS to acquire droplet size.
The literature regarding the Tween 80 -Span 80, it was a 1:1 ratio with the oil, can you direct me to that paper?
Also, because of this thermal cycling I read that it can be partial coalescence that causing this cause phase separation. Any thoughts about this or ways to verify?
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Melting points of pure surfactants do not correlate with their PIT .Did you try centrifugation to ‘time-laps’ your product? It should be fairly easy since you’ve got a DLS device to follow it over time. Does your device allow determination of size distribution too? Then you can ‘read’ from your measurements what happens especially if you’re taking measures at the bottom, middle, and top of the spinning tube.High temp is THE way to go for accelerated chemical stability but not necessarily for a physical one.I’m still confused why exactly 60°C or rather what you’d like to simulate therewith. 60°C ain’t a condition an emulsion commonly experiences unless you’re planning a Venus landing with it or work in the drilling business…
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Besides the PIT. The Span 60 is a solid-state surfactant below 55 degC, I’m thinking it crystallizes and creates a network which can prohibit creaming or just slow it down.
Yes the DLS gives size distribution.
I did not centrifuge my product. What would be the procedure to look at the time lapse of this? Just centrifuge for a period, measure the cream layer, centrifuge again, measure again the top layer, and keep on repeating? How do you correlate that to actually time?
Also, measure the size of the particles for the top, middle, and bottom of the tube? For what purpose really? To see focculation or some other stability?
Sorry, I’m ignorant on the subject and I’m learning. I definitely appreciate your insight.
Well we are trying to use the phase transition of the oil going from solid to liquid and vice versa to store and transport energy (heat) due to latent heat of fusion
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Yes, you can see if it’s flocculation, coalescence, flotation/sedimentation…Okay, phase transition and uhhh…. how cool is that, cosmetics as a new type of battery and fusion power :smiley: . I honestly have no clue what you’re talking LoL. What I understand now, is, that you need phase transition and that one has to be temperature dependent.AFAIK, Spans aren’t usually regarded as alpha-gel builders (that’s what’s often regarded as crystal network). Alpha-gels are commonly formed by surfactant mixtures with fatty alcohols… THIS might be helpful/informative.
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The thing with microemulsions using that system is they are process dependent. Research the lit and you will always find a sonicator used, so chemistry is secondary. You make no mention of a polyol which is nearly critical in a Winsor IV type you describe. Try adding propylene glycol (5-10%) and you may find better results.
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@Pharma
Pretty much cosmetics like a battery lolOkay cool. I’ll look into the lit you linked.
@chemicalmatt
Sonicator or High pressure homoginzer etc. correct?
Any idea why propylene glycol is critical?
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