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  • Water on top of Oil

    Posted by PeiHoong on October 25, 2019 at 3:51 am

    Hi all, 
    Recently I’m working on a triphase product using silicone, aqueous and oil. 
    However, I noticed that there is water layer (orange) on top of the oil phase (yellow). I tried it with 3 types of oil which are Coco Caprylate/Caprate (density 0.859 g/cm3) , Decyl Oleate (density: 0.864 g/cm3)  and Oleyl Erucate (density: 0.868 g/cm3) , all having the same issue. The water I’m using is reverse osmosis water without other additives at this stage. I also tried to add in some salt to increase the cohesion force between water but it doesn’t work. 

    May I know why is it so? Is it the oil phase, the water phase or the dye (Yellow 6 and Yellow 11) having issue?

    Appreciate your advice in advance. 

    Thank you very much. 
     

    Pharma replied 4 years, 6 months ago 3 Members · 10 Replies
  • 10 Replies
  • Pharma

    Member
    October 25, 2019 at 6:52 pm
    Density doesn’t lie but some phases may stick better to glass than others and the difference of surface tension can, under certain circumstances, lead to a ‘wrong’ order of the phases. This phenomenon is usually easier to observe in a separatory funnel but I’ve seen it many times in the lab with water-solvent systems especially if the apparently lowest phase is comparatively small.
    Another explanation might be mixed phases e.g. water containing oil and oil containing water which leads to two differently composed mixed phases where one retains a colour better than another. What is the exact composition?
  • belassi

    Member
    October 25, 2019 at 11:14 pm

    I would first try a colour test. Make the water, say, blue, use a blue water soluble dye. And make the oil yellow, you’ll only need a tiny amount of oil-soluble yellow dye. Since blue and yellow make green, you’ll see immediately if any water has mixed with the oil.
    And make the silicone red. Hopefully you’ll be better able to discern the composition of the layers.

  • PeiHoong

    Member
    October 26, 2019 at 3:50 pm

    @Pharma the ratio is 1:3:1 of oil: water: silicone
    @Belassi can i ask how to make the silicone red without affecting the oil phase colour? cuz if i used oil soluble red for silicone it will affect oil phase as well, isn’t it?

    Thank you

  • belassi

    Member
    October 26, 2019 at 5:10 pm

    Yes, true, you’ll have to try it as two-part samples to see what is going on.

  • Pharma

    Member
    October 26, 2019 at 7:33 pm
    Well, it does look like 4 phases ;) . Anyway, some silicones have a density higher than water… What kind of silicone do you use? Did you try mixing only oil and water or silicone and water to see what happens then? Do you have to use a 1:3:1 mixture? A 1:1:1 is less prone to such an effect.
    Coco caprate/caprylate will float on water (add water first and then slowly drop it on top) but it will readily wet and hence stick to glass and metal surfaces, adding it the other way round can therefore ‘glue’ it to the bottom. With only minor differences in density, thin but broad layers may therefore ‘switch places’. Hence, try a smaller, less broad beaker or even a cylinder = higher liquid column = better hydrostatic effect = less power for the wetting effect. Or don’t use glass but a plastic vessel with a better wetting for water and less so for silicone instead.
    If you’re even adding a silicone oil and shake the triple phases, silicone will cover all the glass surfaces making it even easier for the oil to stick to it and completely impossible for the water to do the same. The pearling effect can be so strong, that water is forced to search for the place with the least surface (which would be a round body or, in this case, one between two liquids rather than a hard surface and a liquid). That might also explain the fourth phase on top which looks like water since water has some affinity for air as a surface to ‘stick to’ and a small amount might therefore be held on top against all laws of gravity and density.
    The smaller your sample, the less important becomes density/buoyancy/sedimentation/gravity whilst effects such as wetting and surface tension become dominating. Because of surface tension, a drop of water on a lotus leaf is nearly spherical, barely touching it, though gravity dictates that it should be completely flat. Some litres water on a lotus leave will however be flat and won’t have a football like form (only the edges will be rounded) because gravity is the dominating force at that scale.
  • PeiHoong

    Member
    October 29, 2019 at 4:53 am

    @Belassi
    @Pharma
    I got a something weird today. Exactly same oil, water and silicone with ratio 1:1:1. There is no more water layer on top, but just that the separation is not really clear cut. There are some water droplets at the bottom and I believe it is due to water stronger adhesive force?  Just that is that mean I just keep my ratio to 1:1:1 and also there is restricted packaging selection to ensure I have clear cut of 3 phases?

  • PeiHoong

    Member
    October 29, 2019 at 4:53 am

  • Pharma

    Member
    October 29, 2019 at 9:00 pm
    What colour is what?
    Give it some time, the ‘cut’ will become sharp after some time.
  • PeiHoong

    Member
    October 30, 2019 at 4:32 am

    @Pharma  blue is water, yellow is oil and silicone. Yes, it has became a very clear cut 3 phases. Hooray~~~Thanks for your advice. 
    But one thing i cant get is why by changing the ratio to 1:1:1 is work but not for 1:3:1….

  • Pharma

    Member
    October 30, 2019 at 6:24 am

    If blue is water in the latest picture and yellow is water in the first picture then it means they’re both the same and water is in the middle… I guess silicone is on the bottom.

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