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 Dipalmitoylphosphatidylcholine (lecithin) Polyoxyethylene(4) lauryl ether (Brij 30)

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

Molecular Architecture Aerosol OTSodium dodecylsulfate (SDS)

Surfactant concentration CMC  Critical Micelle Concentration CMC Below CMC only unimers are present Above CMC there are micelles in equilibrium with unimers

Solution Properties Surfactant concentration CMC Concentration unimers micelles Surfactant concentration CMC Osmotic pressure  (Surfactant concentration) 1/2 CMC Molar conductivity 1/R Surfactant concentration CMC I sc Light scattering

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

Solubility Effects Solubility of a poorly soluble compound increases as a result of solubilization in the micelles Surfactant concentration CMC Solubility

HLB and Use of Surfactants 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 Amphiphilic surfactants are characterized by the hydrophilic-lipophilic balance (HLB): a relative ratio of polar and non-polar groups in the surfactant

Required HLB 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 alcohol15x15/ White wax12x1/180.7 Lanolin10x2/181.1 Total required HLB14.3 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.

HLB of Surfactant Blend 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 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) x = 12x = % Tween 80 and 28 % Span 80 Surfactant blends are commonly used to obtain desired emulsifying properties.