What are surfactants?

Surfactants ◽  
2019 ◽  
pp. 3-16 ◽  
Author(s):  
Bob Aveyard
Keyword(s):  
Water Interface ◽  
Concentrated Solutions ◽  
Dual Nature ◽  
Surfactant Aggregates ◽  
Ionic Adsorption ◽  
Surface Active Agents ◽  
Head Groups ◽  
Surface Active ◽  
Oil Water

Surface active agents (surfactants) are molecules or ions with a dual nature. One or more moieties in a surfactant are ‘water-hating’ (hydrophobic) ‘tail’ groups and one or more are ‘water-liking’ (hydrophilic) ‘head’ groups. Surfactants adsorb from aqueous (or other) solution to various interfaces and in sufficiently concentrated solutions simultaneously aggregate into micelles or other structures. The tail(s) are frequently hydrocarbon or fluorocarbon groups and the head(s) can be polar or ionic. Adsorption and aggregation are often driven by removal of tails from water to an air/water or nonpolar oil/water interface, or to the interior of surfactant aggregates. The ability to adsorb and to aggregate in solution makes surfactants invaluable in industry, in nature, and in the home. Here a brief description is given of the classes of surfactant most commonly encountered, and their usefulness is mentioned. Forward reference is made to appropriate chapters where material is covered in more detail.

Nature of the oil/water interface and equilibrium surfactant aggregates in systems exhibiting low tensions

1988 ◽  
Vol 66 (12) ◽  
pp. 3031-3037 ◽  
Author(s):  
Robert Aveyard ◽  
Bernard P. Binks ◽  
Thomas A. Lawless ◽  
Jeremy Mead
Keyword(s):  
Molecular Structure ◽  
Sodium Chloride ◽  
Water Interface ◽  
Rich Phase ◽  
Aqueous Sodium ◽  
Interfacial Tensions ◽  
Aerosol Ot ◽  
Surfactant Aggregates ◽  
Monolayer Adsorption ◽  
Oil Water

Oil/water interfacial tensions are reported for systems containing pure alkane, aqueous sodium chloride, and a pure anionic surfactant, either Aerosol OT or p-dihexylbenzene sodium sulphonate (DHBS). Evidence is produced to support the claim that monolayer adsorption at the oil/water interface can produce ultralow tensions (~ 1 µN m−1), and that the presence at the interface of a third, surfactant-rich phase is not necessary. The aggregation of DHBS and its distribution between oil and aqueous phases of various salinities have been investigated. It has been confirmed that the behaviour of DHBS in these respects is similar to that of Aerosol OT, as might be expected from its molecular structure. The sizes of microemulsion droplets in equilibrium with planar adsorbed monolayers have been determined, and related to the tensions of the plane oil/aqueous phase interfaces using simple existing theory.

scholarly journals Preparation of Pickering emulsions through interfacial adsorption by soft cyclodextrin nanogels

2015 ◽  
Vol 11 ◽  
pp. 2355-2364 ◽  
Author(s):  
Shintaro Kawano ◽  
Toshiyuki Kida ◽  
Mitsuru Akashi ◽  
Hirofumi Sato ◽  
Motohiro Shizuma ◽  
...  
Keyword(s):  
Colloidal Particles ◽  
Adsorption Property ◽  
Building Blocks ◽  
Pickering Emulsion ◽  
Surface Active Property ◽  
Water Interface ◽  
Pickering Emulsions ◽  
Surface Active ◽  
Oil Water ◽  
Interfacial Adsorption

Background: Emulsions stabilized by colloidal particles are known as Pickering emulsions. To date, soft microgel particles as well as inorganic and organic particles have been utilized as Pickering emulsifiers. Although cyclodextrin (CD) works as an attractive emulsion stabilizer through the formation of a CD–oil complex at the oil–water interface, a high concentration of CD is normally required. Our research focuses on an effective Pickering emulsifier based on a soft colloidal CD polymer (CD nanogel) with a unique surface-active property. Results: CD nanogels were prepared by crosslinking heptakis(2,6-di-O-methyl)-β-cyclodextrin with phenyl diisocyanate and subsequent immersion of the resulting polymer in water. A dynamic light scattering study shows that primary CD nanogels with 30–50 nm diameter assemble into larger CD nanogels with 120 nm diameter by an increase in the concentration of CD nanogel from 0.01 to 0.1 wt %. The CD nanogel has a surface-active property at the air–water interface, which reduces the surface tension of water. The CD nanogel works as an effective Pickering emulsion stabilizer even at a low concentration (0.1 wt %), forming stable oil-in-water emulsions through interfacial adsorption by the CD nanogels. Conclusion: Soft CD nanogel particles adsorb at the oil–water interface with an effective coverage by forming a strong interconnected network and form a stable Pickering emulsion. The adsorption property of CD nanogels on the droplet surface has great potential to become new microcapsule building blocks with porous surfaces. These microcapsules may act as stimuli-responsive nanocarriers and nanocontainers.

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