Surfactants – classification, features and applications N. D. Denkov and S. Tcholakova Department of Chemical Engineering, Faculty of Chemistry, Sofia University, Sofia, Bulgaria Lecture at COST P21 Training School “Physics of droplets: Basic and advanced topics” Borovets, Bulgaria, 12–13 July, 2010
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Surfactants – classification, features and applications
Surfactants – classification, features and applications
N. D. Denkov and S. Tcholakova
Department of Chemical Engineering,Faculty of Chemistry, Sofia University, Sofia, Bulgaria
Lecture at COST P21 Training School “Physics of droplets: Basic and advanced topics”
Borovets, Bulgaria, 12–13 July, 2010
1. Classification of surfactants.
2. Particles as foam and emulsion stabilizers.
3. Role of surfactants for various foam and emulsion properties:
(a) Thin film drainage and stability
(b) Foam rheology
(c) Foam drainage
(d) Ostwald ripening
4. Current directions.
ContentsContents
• Low molecular mass surfactants Nonionic IonicAmphoteric
• Polymeric surfactantsSyntheticNatural
• Particles as surfactant speciesSpherical vs. non-sphericalHydrophilic vs. hydrophobic
1. Classification of surfactants
Low-molecular mass surfactants1. Nonionic surfactantsAlkylpolyoxyethylenes
CnEOm
TweensSpans
2. Ionic surfactants
n=12 ⇒ sodium dodecyl sulfate, SDS
(a) Anionic
Diffuse electric
layer
(b) Cationic
n=12 ⇒ dodecyl trimethyl ammonium chloride, DTAC
3. Amphoteric surfactants
(b) Betaines
(a) Natural soaps (alkylcarboxylates), Lipids
Stabilization of foam films by surfactants
Both can be explained as a result of higher osmotic pressure in the foam film
Electrostatic stabilization by ionic surfactants
Ionic surfactants
Steric stabilization by nonionic surfactants
Nonionic surfactants
Role of surfactant micelles
Solution rheology (shampoos, dish-washing gels)
higher solution viscosity
Structural forces in foam films:
Control of micelle shape: mixtures (SLES+CAPB), counterions (Ca2+), temperature (for EO surfactants)
Comparisonof the low-molecular mass surfactants
Mixtures are usually used in applications(main surfactant + cosurfactant ± polymers)
*Adsorption, surface tension, CMC, micelle size and shape, foam and emulsion stability
Particles (in combination) give new options:Arrest of Ostwald ripening, different rheology, …
Mixtures are often preferred in applications:SDS+LaOH, DTAB+LaOH, SLES+CAPB, CAPB+FAc, LAS+EO7, ...Surfactant + Polymer, Surfactant + Particles
Current activityCurrent activity
• Biosurfactants:
• Polymers-surfactant mixtures.
• Other dynamic phenomena – acoustic response, foam extrusion, ...
• Role of surfactants and polymers in emulsions.
Relevant References
Basic LiteratureK. Tsujii, “Surface Activity: Principles, Phenomena And Applications”,
Academic Press, 1998.
D. J. McClements, “Food Emulsions: Principles, Practices, and Techniques”, CRC Press, 2nd ed., 2005.
K. Robert Lange, “Surfactants: A Practical Handbook”, Hanser, 1999.
J. Goodwin, “Colloids and interfaces with surfactants and polymers”, Wiley 2nd ed., 2009.
B. P. Binks,” Particles as surfactants – similarities and differences”, Current Opinion Colloid Interface Sci. 7 (2002) 21 (review).
S. Tcholakova et al., “Comparison of solid particles, globular proteins, and surfactants as emulsifiers”, Phys. Chem. Chem. Phys. 12 (2008) 1608(review).
N. D. Denkov et al., “Role of surfactant type and bubble surface mobility in foam rheology”, Soft Matter 5 (2009) 3389 (review).
Additional LiteratureS. Tcholakova et al., “Role of surfactant type and concentration for the mean drop
size during emulsification in turbulent flow”, Langmuir 20 (2004) 7444.
S. Tcholakova et al., “Coalescence stability of emulsions containing globular milk proteins”, Adv. Colloid Interface Sci. 123-126 (2006) 259.
K. Golemanov et al., “Selection of surfactants for stable paraffin-in-water dispersions, undergoing solid-liquid transition of the dispersed particles”Langmuir 22 (2006) 3560.
N. D. Denkov et al., "Wall slip and viscous dissipation in sheared foams: effect of surface mobility", Colloids Surfaces A 263 (2005) 129.
S. Tcholakova et al., “Theoretical model of viscous friction inside steadily sheared foams and concentrated emulsions”, Phys. Rev. E 78 (2008) 011405.
K. Golemanov et al., “Surfactant mixtures for control of bubble surface mobility in foam studies”, Langmuir 24 (2008) 9956.
K. Golemanov et al., “Breakup of bubbles and drops in steadily sheared foams and concentrated emulsions”, Phys. Rev. E 78 (2008) 051405.
N. D. Denkov, K. G. Marinova, “Antifoam effects of solid particles, oil drops and oil-solid compounds in aqueous foams”, in Colloidal Particles at Liquid Interfaces, B. P. Binks and T. S. Horozov Eds., Cambridge University Press, 2006.