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SURFACTANTS IN SOLUTION

SURFACTANTS IN SOLUTION. Amphiphilic Surfactants. Amphiphilic surfactants contain a non-polar portion and a polar portion . . Aerosol OT. Classification of Surfactants. Anionic Cationic Zwitterionic Nonionic. Sodium dodecylsulfate (SDS). Cetylpyridinium bromide.

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SURFACTANTS IN SOLUTION

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  1. SURFACTANTS IN SOLUTION

  2. Amphiphilic Surfactants Amphiphilic surfactants contain a non-polar portion anda polar portion. Aerosol OT

  3. Classification of Surfactants • Anionic • Cationic • Zwitterionic • Nonionic Sodium dodecylsulfate (SDS) Cetylpyridinium bromide Dipalmitoylphosphatidylcholine (lecithin) Polyoxyethylene(4) lauryl ether (Brij 30)

  4. 4 nm Surfactant Aggregates Normal micelles Unimers cylindrical spherical Inverted hexagonal phase Reverse micelles Bilayer lamella

  5. Molecular Architecture Aerosol OT Sodium dodecylsulfate (SDS)

  6. 14  12 10 8 CMC 6 4 2 0 0 Surfactant concentration 1 Critical Micelle Concentration CMC Below CMC only unimers are present Above CMC there are micelles in equilibrium with unimers

  7. 14 Concentration unimers 14  Osmotic pressure 12 12 10 10 8 8 CMC 6 CMC 6 micelles 4 4 2 2 0 0 0 1 Surfactant concentration 0 1 Surfactant concentration 14 14 1/R Molar conductivity Isc 12 12 Light scattering 10 10 8 8 CMC CMC 6 6 4 4 2 2 0 0 0 1 0 1 (Surfactant concentration)1/2 Surfactant concentration Solution Properties

  8. Reverse micelles Normal micelles polar compound non-polar compound Solubilization Spontaneous transfer of a compound insoluble in the bulk solvent into solution due to incorporation into the surfactant micelles amphiphilic compound

  9. 14 Solubility 12 10 8 CMC 6 4 2 0 0 Surfactant concentration 1 Solubility Effects Solubility of a poorly soluble compound increases as a result of solubilization in the micelles

  10. HLB and Use of Surfactants Amphiphilic surfactants are characterized by the hydrophilic-lipophilic balance (HLB): a relative ratio of polar and non-polar groups in the surfactant HLB ca. 1 to 3.5: Antifoams HLB ca. 3.5 to 8: Water-in-Oil Emulsifiers HLB ca. 7 to 9: Wetting and spreading agents HLB ca. 8 to 16: Oil-in-Water Emulsifiers HLB ca. 13 to 16: Detergents HLB ca. 15 to 40: Solubilizers

  11. Required HLB HLB needed for emulsification of the oil phase. If there are several oil ingredients the required HLB is calculated as a sum of their respective required HLB multiplied by the fraction of each. • Calculate the required HLB for the oil phase of the following o/w emulsion: cetyl alcohol 15 g., white wax 1g. Lanolin 2 g, emulsifier (q.s.), glycerin 5 g. water 100 g. • Required HLB Fraction • (from reference) • Cetyl alcohol 15 x 15/18 12.5 • White wax 12 x 1/18 0.7 • Lanolin 10 x 2/18 1.1 • Total required HLB 14.3

  12. HLB of Surfactant Blend Surfactant blends are commonly used to obtain desired emulsifying properties. • What is the HLB of the mixture of 40 % Span 60 (HLB = 4.7) and 60 % Tween 60 (HLB = 14.9)? • HLB of mixture: • 4.7 x 0.4 + 14.9 x 0.6 = 10.8 • In what proportion should Span 80 (HLB = 4.3) and Tween 80 (HLB = 15.0) be mixed to obtain “required” HLB of 12.0? • 4.3.(1-x) + 15.x = 12 x = 0.72 • 72 % Tween 80 and 28 % Span 80

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