Basics of emulsions
- 1. BASICS OF EMULSIONS HEMANTH KG MPharm (Pharmaceutics)
- 2. Introduction MICROSCOPIC IMAGE OF EMULSION 2. Coarse dispersion 3. Diameter range of 0.1 to 100 μm 1. Biphasic systems o/w: Oil globules in water Internal External w/o: water globules in oil Internal External FINE EMULSION Globule size: 0.25 to 25 μm Appearance: Milky MICRO EMULSION Globule size: 1 to 100 nm Appearance: Transparent NANO EMULSION Globule size: 1 to 100 nm Appearance: Transparent
- 3. Examples of Emulsions o/w w/o
- 4. Markers of Instability Flocculation Coalescence Creaming BreakingPhase inversion Downward-w/o Upward-o/w Flocs Flocs
- 5. Thermodynamic Instability • Low surface free energy-Stable • Higher interfacial area-higher interfacial energy-Less stable • Globules possess high surface area compared to its original surface area • Globules try going back to original state thereby decreasing ΔA so that ΔG will be zero-Coalescence-Unstable • γo/w may be reduced but cant be made zero-dispersed phase certain +ve interfacial tension. • So ΔG can’t be made Zero • γo/w can be made minimum by adding Surface active agents-Emulsifying agents ΔG=increase in surface free energy γo/w = interfacial tension of oil-water interface ΔA = increase in surface area of the interface due to droplet formation ΔG = γo/w ΔA
- 6. Appearance and identification tests Other tests are • Ferric chloride test, • Fluorescence test, • Filter paper test, with limitations Dye solubility test Amaranth dye Water soluble dyes: Amaranth Methylene blue Oil soluble dyes: Sudan III Scarlet red Dilution test o/w w/o Water o/w Conductivity test o/w- Bulb glows w/o- Bulb doesn’t glow Creaming test o/w Upward Creaming w/o Downward Creaming These are the standard tests which give authentic results.
- 7. How to improve stability ? 5. Temperature fluctuations: • Chemical degradation • o/w-Water evaporation-concentrated • Low temp-ice crystals • Decrease viscosity 2. Particle size: • Globule size , Brownian movement • Stokes’ law-diameter of globule is major factor • 4 fold Creaming , globule diameter ½ • Optimum globule size-max stability 3. Particle size distribution: • Uniform globule size-loosely packed, less contact • Uniform globule size-small globules occupy voids of larger globule: Coalescence • Monodisperse system-difficult, hence optimum degree of size distribution 1. Viscosity: • As viscosity , flocculation • Brownian movement , leading to creaming • Hence, optimum viscosity is desired 4. Phase volume ratio: • Relative volume of w/o • Max 74% oil-lead to breaking • Critical point-conc of internal phase above which-instability • Beyond critical point-irregular globule shapes-coalescence
- 8. Preservation • Carbohydrates, proteins, sterols and gums are present in emulsions • Microbes: fungi, bacteria, yeast use for their growth and cause instability • Parenteral emulsion: Sterility must • Hence optimum preservative quantity is added. • E.g. Benzoic acid, sodium benzoate, methyl paraben, propyl paraben
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