1. In oil in water emulsions, the oil droplets are dispersed in the water phase. It doesn’t mater which phase is poured into which in an oil in water emulsion. However in a water in oil emulsions, the water droplets  (internal phase)are dispersed in the (external oil phase )and it is important here that the water phase is actually poured into the oil phase to form a stable emulsion.
  2.  The HLB scale ranges from 0 to 20, with 10 corresponding to an emulsifier that is equally attracted to water and oil. Emulsifiers with HLB values greater than 10 are more hydrophilic and thus better at stabilizing o/w emulsions. In contrast, emulsifiers with HLB values less than 10 are more hydrophobic and therefore better suited for w/o emulsions.
  3. All emulsions, whether o/w or w/o, require an emulsifier to provide them with stability; o/w emulsions often require more than one emulsifier for optimal stability, but a variety of emulsifiers exist to suit this function. Polysorbate, sorbitan laurate, and cetearyl alcohol are just a few examples of emulsifiers that are compatible with o/w emulsions. However, because the hydrophilic balance must be within a range of approximately 3-6, there is a limited number of emulsifiers to select from. Sorbitan stearate, lecithin, lanolin/lanolin alcohols, and glyceryl monooleate are some examples of viable w/o emulsifiers.
  4. In making water in oil emulsions, you  test the ph of the water phase ingredients and adjust appropriately, whereas in oil in water emulsions you check and adjust ph at the end of the emulsion process.
  5. To increase viscosity of water in oil emulsions, you have to increase viscosity of oil phase only, whereas you can use rheological modifiers to thicken water phase in oil in water emulsions to increase viscosity.

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