Home Cosmetic Science Talk Formulating Emulsions Questions

  • Emulsions Questions

    Posted by beautysci on April 23, 2014 at 12:10 pm


    I’ve been reading up on emulsions and have some questions:

    1) Can you see flocculation/coagulation occuring? I know you can see creaming and sedimentation occuring but I’m not sure about flocculation/coagulation.

    2) How can you make water less dense so that it can be closer to the density of the oil phase in an emulsions? Can adding glycerin make the water phase less dense? Also, how can you increase the density of the oil phase? Can you do this by adding high molecular weight oils?

    3) Should you only add thickeners to the continuous phase of an emulsion (for stability)?

    4) Why are anionic emulsifiers not compatible in cationic environments and vice versa?

    5) When looking at a formula, how do you determine which emulisifier is the primary and which is the secondary emulsifier?

    I know this is a lot but I appreciate any help. Thanks!

    chemist77 replied 9 years, 7 months ago 4 Members · 3 Replies
  • 3 Replies
  • bill_toge

    April 23, 2014 at 5:40 pm

    1) yes - the emulsion will look less smooth, can appear more translucent and can lose some of its uniformity

    2) in general, you can’t easily match the densities of the oil and water phase; also, glycerine will have the opposite effect, as it’s denser than water - about 1.3 g/cm3 at room temperature if I remember rightly (water is about 1.0 g/cm3)

    besides, in practise the density difference is pretty insignificant compared to the other factors governing emulsion stability (dispersed droplet size, nature and amount of emulsifiers, rheology of continuous phase)

    3) you can add thickeners to the dispersed phase if you want, but they’d mainly affect the emulsion’s rub-out properties and have a very marginal effect on the stability

    4) positive and negative charges are attracted to each other; if your charged emulsifier is drawn away from the interface of the continuous and dispersed phases by attraction to an oppositely-charged substance in the continuous phase, your emulsion will eventually break down

    5) no general answer to this one, it depends very much on the formula!

  • Bobzchemist

    April 23, 2014 at 6:58 pm

    1) Put red wine vinegar and vegetable oil into a bottle and shake vigorously, then let it sit and observe. 

    Add an egg yolk and repeat.
    2) Matching water/oil phase densities typically does nothing for the types of macro-emulsions we make for cosmetics. The micro-emulsions made for food and drinks are a different story. Look up weighting agents, which make flavor oils more dense.
    more later…
  • chemist77

    April 23, 2014 at 9:41 pm

    @Bill great explanation

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