Emulsions Defined
  • Thermodynamically unstable system of two immiscible liquids, one dispersed within the other as small globules
Dispersed Phase
  • Droplettes within the emulsion
  • aka internal phase
Continuous phase
  • Liquid in which the droplettes are suspended
  • aka external phase
Uses of emulsions
Types of Emulsions
  • Oil-In-Water O/W

  • Water-in-Oil W/O

  • Oil-In-Water-in-Oil O/W/O (Rare)
  • Water-In-Oil-in-Water W/O/W (Rare)
Methods for determining the type of an unknown emulsion
  • Water soluble dyes (e.g. methylene blue)
  • Diluting with the appropriate solvent
  • Conduction

    • O/W have a high conductance
Types of Emulsifying agents
  • Surface Active Agents
  • Hydrophilic Colloids
  • Finely Divided Solid Particles
  • Auxiliary Emulsifying Agents
Rule of Bancroft
  • The type of emulsion depends on the characteristics of the surfactant
  • The phase in which the surfactant is most soluble becomes the continuous phase
Surface Active Agents
  • aka Monomolecular Adsorption
  • Classical idea of polar micelles dividing polar and non-polar materials
  • Reduce surface tenions(?)
  • Micelles may be composes of more than one surfactant acting together

    • e.g. Tween 40 /Span 80
Finely Divided Solid Particles
  • aka Particulate film
  • Particles can be wetted by hydrophillic and hydrophobic agents, causing particles to collect at the interface
Examples of Particulate film Agents
  • Bentonite
  • Veegum
  • Hectorite
  • Magnesium Hydroxide
  • Aluminum Hydroxide
  • Magnesium Trisilicate
Auxiliary Emulsifying Agents
Mechanisms of Emulsion Breakdown
  • Micelle loss

    • Breaking the film surrounding the micelle
    • Coalescing of micelles
    • Aggregation of micelles within coalescing
  • Phase Inversion

    • Swapping of the internal and external phases
    • Adding divalent electrolytes may cause phase inversion

      • Switching of a soft soap to a hard soap
    • Changing the ratio of internal and external phase may cause inversion
Preserving Emlusions
  • Preservatives should be in the aqueous phase, regardless of internal or external
  • Preservatives should be in the unionized form
  • Preservatives should not interact chemically with other constituents
Preparation Methods of Emulsions
Continental Method
  • aka Dry Gum Method
  • Prepare the primary emulsion of 4 Oil : 2 Water : 1 Surfactants
  • Surfactant usually Gum Arabic

Process

  1. Wet surfactant with oil phase in mortar
  2. Add water all at once
  3. Additional water can be added after the primary emulsion is prepared
  4. Add active ingredients as a solution to the primary emulsion
  5. Add any potentially destablizing agents (e.g. alcohol) at the end of the process
  6. Finally QS with water to final volume
  • Cod liver oil (Vitamin A source) is prepared by the continental method
English Method

aka wet Gum Method

  • Proportions are the same as the Continental Method, but the process is different italicized steps are the different steps
  • More difficult to use, but produces a mores stable product
  • Produces O/W emulsion
  • Prepare the primary emulsion of 4 Oil : 2 Water : 1 Surfactants

    • Surfactant usually Gum Arabic

Process

  1. Wet surfactant with water phase in mortar
  2. Slowly add oil phase, triturating continuously
  3. Continue triturating for several minutes to form the primary emulsion
  4. Additional water can be added after the primary emulsion is prepared
  5. Add active ingredients as a solution to the primary emulsion
  6. Add any potentially destablizing agents (e.g. alcohol) at the end of the process
  7. Finally QS with water to final volume
Bottle Method

Process

  1. Surfactant is added to a bottle
  2. Oil is added to the bottle
  3. Throughly shake
  4. Immediately add water

    • Allowing the surfactant and oil to sit will create a waterproof material difficult to mix
  5. Shake until primary emulsion is formed
  6. Additional water can be added after the primary emulsion is prepared
  7. Add active ingredients as a solution to the primary emulsion
  8. Add any potentially destablizing agents (e.g. alcohol) at the end of the process
  9. Finally QS with water to final volume
Auxiliary Method

Emulsions from the Continental Method, English Method, or Bottle Method can be improved by running them through a homogenizer. This process generally produces droplettes of 5 microns or less

Nascent Soap Method
  • Mix equal volumes of oil phase (olive oil, oleic acid) and Lime Water
  • Ca++ ions pair with two fatty acids, creating a very lipophilic solution, therfore a water in oil emulsion
  • Can be prepared in a bottle or with a mortar if some ingredients are insoluble
How are drugs added to O/W emulsions
  • The goal is to get the drug into the internal phase, not the external phase
  • Hydrophillic drugs should be mixed with an oily material so the drug goes into the micelles
  • Oily drugs can be mixed with a oily solvent and added to the emulsion
Microemulsion
  • Thermodynamically Stable

    • Form spontaneously
  • Optically transparent
  • nanometer sized particles
  • Form in O/W or W/O
Uses of Microemulsions

Additional Resources

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