SURFACTANTS IN SOLUTION

Classification of Surfactants Anionic Cationic Zwitterionic Nonionic Sodium dodecylsulfate (SDS) Cetylpyridinium bromide You will find many other examples of amphiphilic surfactants in the recommended literature Dipalmitoylphosphatidylcholine (lecithin) Polyoxyethylene(4) lauryl ether (Brij 30)

Surfactant Aggregates Normal micelles Unimers cylindrical spherical Inverted hexagonal phase Molecules of amphiphilic surfactants in solution self-assemble into various supramolecular aggregates. This slide shows typical changes in surfactant self-assembly and morphologies formed with decreasing water content in the system (water content decrease is shown by arrows) Reverse micelles Bilayer lamella 4 nm

Critical Micelle Concentration CMC 2 4 6 8 10 12 14 1 Surfactant concentration CMC  Below CMC only unimers are present Above CMC there are micelles in equilibrium with unimers Critical micelle concentration (CMC) can be determined by surface tension measurements. Below CMC surfactant adsorbs on the surface and decreases surface tension. More surfactant we have below CMC less surface tension is. Above CMC the micelles are formed. All surfactant added in excess of the CMC incorporate in the micelles. Therefore surface tensions remains the same as at CMC.

Solution Properties Surfactant concentration CMC Concentration 2 4 6 8 10 12 14 1 Surfactant concentration CMC Concentration unimers micelles 2 4 6 8 10 12 14 1 Surfactant concentration CMC Osmotic pressure  Dependencies of various solution properties on surfactant concentration reveal a break upon crossing the CMC as a result of micelle formation. This underlies methods for determining CMC by measuring such properties as a function of the surfactant concentration. 2 4 6 8 10 12 14 1 Surfactant concentration CMC Isc 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 2 4 6 8 10 12 14 1 Surfactant concentration CMC Solubility One method to characterize CMC of a surfactant in aqueous solution is to determine solubility of a water-insoluble dye as a function of surfactant concentration. Above CMC the dye is transferred into solution due to incorporation into the core of the micelles.

An example of an HLB value calculation BRIJ ® 98 INCI name : oleth-20 is a 20 mole ethoxylate of oleyl alcohol calculate the molecular weight of the 20 moles of ethylene oxide ( one mole ETO =44 ); 20 x 44 = 880 add this number to the molecular weight of the oleyl alcohol; 880+ 270 = 1150 ( the mol. wt of BRIJ 98 ) What percentage of 1150 is 880 ? 880/1150 = 76.5% 76.5% divided by 5 = 15.3 15.3 is the HLB value of BRIJ 98

Important to remember !

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 HLB is an arbitrary parameter. Sometimes it is determined experimentally, for example, using reverse phase chromatography. There are numerous methods of computing of HLB. More information on computing of HLB (including blends of surfactants and requred HLB) can be found in: M. Stoklosa and H. Ansel, Pharmaceutical Calculations, Williams & Wilkins, Baltimore, 1996.

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 HLB is an arbitrary parameter. Sometimes it is determined experimentally, for example, using reverse phase chromatography. There are numerous methods of computing of HLB. More information on computing of HLB (including mixtures of surfactants) can be found in: M. Stoklosa and H. Ansel, Pharmaceutical Calculations, Williams & Wilkins, Baltimore, 1996.

HLB of Surfactant Blend Surfactant blends are commonly used to obtain desired emulsifying properties. Span 60 (HLB = 4.7) Tween 60 (HLB = 14.9) Span 80 (HLB = 4.3) Tween 80 (HLB = 15.0) HLB is an arbitrary parameter. Sometimes it is determined experimentally, for example, using reverse phase chromatography. There are numerous methods of computing of HLB. More information on computing of HLB (including mixtures of surfactants) can be found in: M. Stoklosa and H. Ansel, Pharmaceutical Calculations, Williams & Wilkins, Baltimore, 1996.

What is the HLB of the mixture of 40 % Span 60 (HLB = 4 What is the HLB of the mixture of 40 % Span 60 (HLB = 4.7) and 60 % Tween 60 (HLB = 14.9)? Sorbitan monostearate is an ester of sorbitol and stearic acid (synthetic wax) Polyoxyethylenesorbitan monooleate; Sorbitan monooleate ethoxylate 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 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

Glycerol Monostearate HLB value of 3.6~4.2 dissolves in hot grease, paraffine, ethanol, chloroform, acetone and aether, the material is widely used when producing of chocolate, margarine, ice cream, skin care balsam, cold cream, hair oil and drug ointment, also lubricant for plastic processing

Shampoo

Ingredients Isobutane Cyclomethicone Aluminum Chlorohydrate Propylene Glycol Dicaprylate/Dicaprate Lichen extract Fragrance Quaternium-18 Silica Dimethiconol

cyclomethicone Propylene Glycol Dicaprylate/Dicaprate

Facial Cleanser Aqua/Water Palmitic acid Myristic acid Lauric acid Stearic acid Potassium hydroxide PEG-7 Glyceryl cocoate PEG-150 Distearate Glycerin Sodium laureth sulfosuccinate Limonene Linalool Zinc PCA Propylparaben Propylene glycol Disodium EDTA NaCl

Propylene glycol propyl ester of p-hydroxybenzoic acid = propylparaben zinc salt of 2-Pyrrolidone-5-Carboxylic Acid PEG-7 Glyceryl cocoate Polyoxyethylene glycol glyceryl cocoate (monococoate).

PEG-150 Distearate Polyethylene glycol diester of stearic acid. Sodium laureth sulfosuccinate

Cream