Competing processes Dispersion of one immiscible liquid into another increases

Competing processes dispersion of one immiscible

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Competing processes Dispersion of one immiscible liquid into another - increases free energy of the system Combination of droplets to reform the initial liquids - reduces free energy - spontaneous process Can we do something to reduce the free energy while dispersing one phase into another? Ways to stabilize dispersed droplets Approach # 1 Thermodynamic stabilization Reduction of free energy by reduction of interfacial tension between two phases Long-term stability Approach # 2 Mechanical stabilization Formation of a rigid interfacial film around the dispersed droplets Short-term stability Types of EMULSIONS 1. O/W - oil is dispersed in water - inner phase oil, outer phase water 2 . W/O - water is dispersed in oil - inner phase water, outer phase oil 3. Multiple Emulsions: W/O/W, O/W/O Structure of Pharmaceutical Emulsions Copyright rules apply 2 of 20
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Identification of Emulsions – O/W OR W/O 1. Dilution Test (miscibility Test) 2. Conductivity Test 3. Dye Solubility Test (staining test) RED WATER-SOLUBLE DYE O/W OR W/O O/W OR W/O Copyright rules apply 3 of 20
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Mechanism of Action of Emulsifying Agents (Ref: Remington: The Science and Practice of Pharmacy, 22 nd ed, p. 745, Vol. I, 2013)) Type of film Examples Mechanism Monomolecular Anionic Soap Potassium laurate Cationic Soap Quaternary ammonium compounds Nonionic Tween (polyoxyethylene sorbitan fatty acid ester), Span (sorbitan fatty acid ester) 1. Surface active agents 2. Reduce interfacial tension 3. Can form either W/O or O/W emulsion , depending on the surfactant nature, composition of medium 4. Coherent, flexible film 5. Very efficient emulsifying agent Multimolecular Acacia Gelatin Polyvinyl alcohol 1. NOT a surface-active agent 2. Do NOT reduce interfacial tension 3. Can form ONLY O/W emulsion 4. Strong Rigid film Fine solid particles Bentonite Magnesium hydroxide 1. NOT a surface-active agent 2. Do NOT reduce interfacial tension 3. Can form either O/W or W/O emulsions , depending on the method 4. Particles must be wetted by both phases 5. Must be very small compared to dispersed phase Type of emulsion ****** 1. Percentage of dispersed phase and dispersion medium, internal phase cannot be more than 60% 2. Solubility of the emulsifying agent in the external phase Copyright rules apply 4 of 20
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Formulation of Emulsion Active ingredient - Structural Formula, Melting point and polymorphism, Solubility, Stability, Dose, Chemical incompatibilities Choice of emulsifying agent HLB (hydrophilic lipophilic balance) of surfactants HLB - Solubility in aqueous phase - forms O/W emulsion HLB - Solubility in oil phase - forms W/O emulsion Blending of emulsifying agents To produce required HLB value To increase stability of interfacial film To improve consistency and feel of the product Choice of emulsion type Most oral emulsions for administration of fats or oils are o/w type - Water in outer phase is pleasant to take, easier to flavor Parenteral emulsions for IV must be o/w type, IM for depot administration may be w/o type
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  • Fall '09
  • Emulsion, C. Emulsion

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