Surfactant association structures and the stability of emulsions and foams

Abstract

Traditional surfactants in combination with water and a more hydrophobic amphiphile, such as an alcohol or a carboxylic acid, present a rich variety of colloidal association structures, both micelles and lyotropic liquid crystals. The presence of such association structures has a pronounced influence on the stability of macrodispersed systems such as emulsions and foams. A few examples of such an influence are discussed.

Sandwich Structures at Oil–Water Interfaces under Alkaline Conditions

“…The possibility of liquid crystal stabilization of crude oil and water emulsions was suggested by Sjöblom and coworkers, (9) who published extensively on crude oil emulsions (10)(11)(12)(13)(14). Liquid crystal role in emulsion stabilization has been studied in equilibrium systems (15)(16)(17)(18)(19)(20)(21). The dynamics of the equilibration process between phases containing model surfactants and cosurfactants was also studied (22)(23)(24)(25)(26)(27)(28); however, to our knowledge, the formation of liquid crystal and its role on emulsion stability has not been studied on real crude oil systems of industrial importance.…”

Phase Behavior of Sodium Naphthenates, Toluene, and Water

“…Other phases may be formed in the system (1) due to the ability of surfactant molecules to self-assemble into micelles and inverted micelles capable of solubilizing substantial amounts of oil and water, respectively. Lamellar liquid crystals can also be formed, especially at a water/oil interface, drastically increasing emulsion droplet stability against coalescence (2)(3)(4).…”

The Effects of Emulsifiers and Emulsion Formulation Types on Dermal and Transdermal Drug Delivery

“…surfactants, polymers, solid particles), and often the stabilisation effect of emulsifi ers can be attributed to more than one method. For instance, some surfactants may form a monolayer at the oilwater interface, whilst an excess thereof may also arrange in liquid crystalline structures in the aqueous phase, which could improve emulsion stability by preventing coalescence (Friberg and Solans 1986 ). Hydrophobically modifi ed watersoluble polymers can stabilise o/w emulsions by adsorbing at the oil-water interface (hydrophobic part of the polymer), as well as by gelation of the aqueous continuous phase (hydrophilic part of the polymer) (Eccleston 1997a ).…”

“…In addition to the formation of a surfactant monolayer at the oil-water interface, some surfactants, when in excess, may arrange in liquid crystalline structures in the aqueous phase, which may aid the stabilisation of emulsions (Friberg and Solans 1986 ) and could affect skin permeation. Only two studies are mentioned below to illustrate the effect of the emulsifi er association structures on skin permeation.…”