Vitamin C also protects the skin from harmful effects of uv rays. Slow and sustained release from internal depot in to the continuous phase (generally water in a w/o/w system). Incorporation of incompatible materials Multiple emulsions are used in cosmetics & skin care products (fine texture, smooth feel): sunscreens, shaving creams, antiperspirants preparation methods- On a small scale(in the lab or pharmacy): Equipment: Mortar and pestle, mechanical blender, homogenizer Three methods: 1. Dry gum method: (continental method) o The emulsifying agent (acacia) is mixed with the oil before addition of water. Also called the 4:2:1 method(4parts of oil, 2 parts of water, 1 part of gum). o Example: to emulsify 40 ml of oil, 20ml of water, 10g of gum is required. o To emulsify mineral oil, 3:2:1 (greater proportion of surfactant) o A porcelain mortar is preferable for trituration (glass surface is too smooth to provide a grinding action). 2. Wet gum method: (English method) same proportion (4:2:1) as in dry gum method. o The emulsifying agent is mixed with water (in which it is soluble), then the oil is slowly incorporated. 3. The bottle method (shaking). Reserved for volatile oils and non-viscous oils One part acacia is placed in a bottle, 4 parts of the oil added, thoroughly shaken, required volume of water(2 parts) is added and mixed thoroughly. Not suitable for viscous oils. The prepared emulsions may be further passed through a hand homogenizer/blender. o This will reduce the particle size to about 5microns. emulsion needs a surfactant, chemistry - most effective is non-ionic surfactant… will form both w/o and o/w types Anionic surfactants Soaps: Sodium and potassium salts of st.chain fatty acids (12-18 carbon atoms).eg: sod.oleate, sod.stearate. Used to prepare o/w emulsions
o Unstable below pH 7. If acid is added, free fatty acids will be precipitated. emulsifying property is lost in acid condition o Incompatible with polyvalent cations. o External use Sulfated compounds- anionic Sodium lauryl sulfate (SLS): o Produce o/w emulsions o Stable over wide pH range o Fairly resistant to divalent metal ions Cationic surfactants Quaternary ammonium compounds Cetyl trimethyl ammonium bromide (cetrimide) Incompatible with anionic surfactants, polyvalent anions and high pH. Infrequently used as emulsifiers: Toxicity, irritancy. Used as detergents and as preservatives in topical formulations Non-ionic surfactants Glycerol esters Glyceryl monostearate: strongly hydrophobic, produce w/o emulsions Sorbitan esters (Spans)- Esterification of one or more hydroxyl groups of sorbitan with lauric, oleic, palmitic or stearic acid. Produce w/o emulsions. Polysorbates: polyoxyethylene derivatives of sorbitan esters (Tweens). o Compatible with most anionic, cationic, non-ionic materials o Low toxicity, irritancy o Stable to heat, acid, electrolytes o Produce o/w emulsions o Used in both parenteral and non parenteral emulsions.
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- Fall '16
- Raake, Sara