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I added 100 g coconut oil, 100 g distilled water and 500 mg lecithin to an 1800 watt blender. The motor from the blender has has a passive heating action. I blended it at full for four minutes. The result seemed to be a hot, uniform substance with a thin layer of foam on top.

I poured this mix into a smaller container and placed it in the fridge. After a while it set into a solid, uniform substance with no apparent precipitation.

I then heated the substance in the microwave for thirty seconds. When I removed it, the components had separated and precipitated. Cooling it in the fridge again resulted in a delicate solid sheet at the top which broke through to liquid underneath.

Why did the mix precipitate (presumably de-emulsify) after being microwaved but not occur when blended?

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  • $\begingroup$ After cooling in the fridge the second time - (1) Is there some sort of ppt still? (2) Did you try blending it again? // Emulsions are temperature sensitive. // A ppt after second cooling in fridge would indicate that an irreversible reaction has taken place and that probably the mixture won't be able to be emulsified again. // You do realize that heating in a microwave isn't absolutely uniform, especially when dealing with a solid. $\endgroup$
    – MaxW
    Commented Apr 13, 2016 at 16:07
  • $\begingroup$ When I get emulsions in my workups, I often hit the sep funnel with a little heat from the heat gun (assuming my product isn't terribly heat-sensitive). This seems to help things separate. The heat from the blender may not have been helping emulsify at all -- it may well have worked better making the emulsion if it was colder. $\endgroup$
    – SendersReagent
    Commented Apr 13, 2016 at 16:46

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The simple explanation is that the speed of de-emulsification depends strongly on physical state and temperature.

If you have created a solid emulsion by cooling the initial blend, the de-emulsification will be very slow as there is little scope for the components to move around at all never mind separate. warming this solid up so it liquefies creates two factors that make separation easier: the mixture liquefies and the temperature rises, creating many easier ways for separation to occur. Once separation has occurred only re-blending will restore the emulsion.

Emulsions often separate slowly (milk, for example, slowly forms a layer of creamier fat on top but it doesn't happen quickly after thorough mixing). In your case the initial cooling "froze" the emulsion but the microwave heating enabled de-emulsification to occur by heating the mix. Cooling the result without blending is not going to restore the emulsion without further blending.

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How long did yoi leave it to settle? Maybe it takes yet longer time to settle down than what you gave it?

Another idea is that either microwaves or heat influenced the emulsion structure and broke the oil-water complex?

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