Help on Creating Oil (Non-ionic fatty acid) Emulsions in Water

[FishLove]

Hello I am graduate student at a university working on a M.S. in environmental science.

 

I am asking for advice on creating emulsions in water beakers with lipids (poly unsaturated fatty acids). I want to create emulsions with fatty acids like DHA (docosahexaenoic acid, 22:6(n-3)). Seeing as how they are not saturated they should have some solubility in water...at pH 8 it is predicted at around a few grams/liter. However when I dispense 20 to 10 mg into a 1 L of water lipid droplets/vesicles still form, even after shaking vigorously. So as of now I have little hope of dissolved monomers but I want to at least create a 'stable' emulsion, or micro/nanoemulsion, that will last at least 24 hours.

 

What is the best method to emulsify a sparingly soluble nonpolar compound in predominantly water (polar) matrix? I can't use alot of solvent (limited to 0.1% by volume).

 

I have researched some possible methods;

 

1. Sonication for long periods of time (hours)

 

2. Handling methods to prevent formation of micelles/vesicles/droplets of fatty acid oil (e.g. adding very minute amounts at a time while vortexing... this could affect precision of final concentration though)

 

3. Saponify the fatty acids (e.g. add fatty acids to a alkaline solution, giving all the fatty acids a polar RCOOH- charge, making them more miscible), vortex them, and gently neutralize the solution with acid, bringing the micelles back into formation but creating homogenous mixture of micelles? would this work? My final product has to be something with around 10 mg/L of fatty acid in around 8 pH hardwater.

 

Thank you all for your advice,

Edited February 3, 2011 by FishLove

[Mr Skeptic]

Being unsaturated won't make them particularly polar, though I suppose it would at least help a little by making them more liquid. I don't really know but I would think that even with some dissolved some of it would still form micelles, in equilibrium with the dissolved lipid? Does your final product have to have the 10 mg/L dissolved or is it OK if some of it is in micelles? Is it OK if your product has a detergent/surfactant? In any case, heating will help in combination with pretty much any other method.

[hypervalent_iodine]

Are you sure these will dissolve? Do you have references for that? As Mr Skeptic said, being unsaturated will not make them any more or less polar. It is still a hydrophobic alkyl chain with a hydrophilic carboxylate on on end. I am not at all surprised that your emulsion is coalescing and/or creaming with an alkyl chain that massive. Carboxylic acids any larger than about 5 carbon long tend to be poorly soluble. Are you using any surfactants? By the sounds of it, you have very little chance of this succeeding without them.

 

Also, adding a fatty acid to a basic solution will turn it into a carboxylate, which is RCOO- not RCOOH. Also, you wouldn't be saponifying in the traditional sense, since base catalysed saponification is the reaction of an ester with a strong base to produce the acid and the alcohol. You already have the acid, so there's no point. What you're suggesting is simply shifting the deprotonation equilibrium of the acid towards the products side by increasing the pH (sodium hydroxide is fine for this). Still though, when you convert back to the acid you'll probably be left with the same problem of coalescing/creaming. If you aren't, well then the reaction is still pretty pointless because sonicating it will achieve the same thing with less chemical wastage.

Edited February 3, 2011 by hypervalent_iodine

[CaptainPanic]

I want to create emulsions with fatty acids like DHA (docosahexaenoic acid, 22:6(n-3)). Seeing as how they are not saturated they should have some solubility in water...at pH 8 it is predicted at around a few grams/liter. However when I dispense 20 to 10 mg into a 1 L of water lipid droplets/vesicles still form, even after shaking vigorously. So as of now I have little hope of dissolved monomers but I want to at least create a 'stable' emulsion, or micro/nanoemulsion, that will last at least 24 hours.

 

What is the best method to emulsify a sparingly soluble nonpolar compound in predominantly water (polar) matrix? I can't use alot of solvent (limited to 0.1% by volume).

You try to make an emulsion, so the solubility is not very relevant. It only shows that there are lipids left to make an emulsion, because they do not dissolve.

 

Well known microemulsions of lipids in water are: milk or mayonaise. Milk seems closer to what you try to achieve (just a little lipids, and quite a lot of water). So, I suggest that you investigate the stability of milk to get an idea. In case your emulsion has to be food grade: all the ingredients in milk are food-grade as well.

It's quite unlikely that your particular lipids will actually form a stable microemulsion in normal water by only adjusting the pH. You probably need a few more additives (emulsifier). Here's a little text (wikipedia) on the stability of emulsions.

Edited February 3, 2011 by CaptainPanic

[FishLove]

Thank you all for your quick replies and comments, they are at least encouraging. The ultimate problem I have with making solutions is I must expose living algae to these fatty acids... and tox protocolos limit solvent usage to 0.1-1% of total volume,otherwise I would load up on the solvents/surfactants. Maybe food grade stabilizers, thickeners, or surfactants such as lecithin may be used, but these appear to be slightly toxic or may alter the toxicity of fatty acids anyways by coating the lipids. And I don't have a sonicator... some I am testing some food grade DHA with a shaker and intense stirring... I suppose what I am aiming at is increasing the energy of the droplets so that they may be dispersed as possible (I believe I can potentially quantify oil droplet density later with spectroscopy or haemocytometer) for at least 24 hours. Eventually the free energy of the droplets in the system will decrease and droplets will coalesce... and I can't fight physics.

[mississippichem]

Have you tried adding low molecular weight polyethylene glycol?

[FishLove]

Polyethylene glycol looks like it would be a good surfactant. But I don't believe I'll be allowed to use surfactants as these change the interactions of the chemical with living aquatic life membranes..

I have have applied a shaker for several hours to an approx 10mg DHA /liter deionized water; the emulsion appears stable after 24 hours, and even maintains its cloudy appearance after 48 hours. Some droplets mix well into the solution (with a microscope they appear on average a few microns in length) but I still observe some droplets of oil on the surface of the media. I suppose I will need to find the water accommodated fraction of the oil, but in regards to forming emulsions for testing, prospects look good. Perhaps I can enumerate droplet size, volume, density with microscopes or look at turbidity/light dispersion with a spectrophotometer. One last question though,

 

1. Would adding a simple organic solvent (e.g. methanol) increase the stability of the oil in water emulsion or decrease it?

 

Thank you all.

[mississippichem]

Polyethylene glycol looks like it would be a good surfactant. But I don't believe I'll be allowed to use surfactants as these change the interactions of the chemical with living aquatic life membranes..

I have have applied a shaker for several hours to an approx 10mg DHA /liter deionized water; the emulsion appears stable after 24 hours, and even maintains its cloudy appearance after 48 hours. Some droplets mix well into the solution (with a microscope they appear on average a few microns in length) but I still observe some droplets of oil on the surface of the media. I suppose I will need to find the water accommodated fraction of the oil, but in regards to forming emulsions for testing, prospects look good. Perhaps I can enumerate droplet size, volume, density with microscopes or look at turbidity/light dispersion with a spectrophotometer. One last question though,

 

1. Would adding a simple organic solvent (e.g. methanol) increase the stability of the oil in water emulsion or decrease it?

 

Thank you all.

 

It should help depending on the solvent's LogP value. If you can get your hands a copy of ChemDraw it has a database of LogP and cLogP values.

[CaptainPanic]

Polyethylene glycol looks like it would be a good surfactant. But I don't believe I'll be allowed to use surfactants as these change the interactions of the chemical with living aquatic life membranes..

I have have applied a shaker for several hours to an approx 10mg DHA /liter deionized water; the emulsion appears stable after 24 hours, and even maintains its cloudy appearance after 48 hours. Some droplets mix well into the solution (with a microscope they appear on average a few microns in length) but I still observe some droplets of oil on the surface of the media. I suppose I will need to find the water accommodated fraction of the oil, but in regards to forming emulsions for testing, prospects look good. Perhaps I can enumerate droplet size, volume, density with microscopes or look at turbidity/light dispersion with a spectrophotometer. One last question though,

 

1. Would adding a simple organic solvent (e.g. methanol) increase the stability of the oil in water emulsion or decrease it?

 

Thank you all.

A simple organic solvent (such as methanol) will change the interactions of the chemical with the living aquatic life more than most surfactants. In fact, it might kill it. It will also increase the solubility of the oil in the water+methanol phase.

 

I'm still confused a bit what you try to achieve actually. You seem to mix the concepts of "emulsion" and "solution"... but physically, these are very different things...

 

The primary question is: can your algae consume the lipids from the liquid lipid phase (lipids are not dissolved)? Or should the lipids be dissolved in the aqueous phase? As I said before: these are two very different things. Increasing the solubility of the lipids is a completely different problem than increasing the emulsion stability.

[lkayne]

There are "weighted" oils out there. For example brominate vegetable oils (BVO). Also items like Ester Gum, Sucrose Acetate Isobutyrate or Damar gum can be used.