Surfactants form a unique class of chemical compounds. This review provides an introduction to the nature and physical properties of surfactants, emphasizing their ability to radically alter surface and interfacial properties and to self-associate and solubilize themselves in micelles. These properties provide the means to apply surfactants in wettability modification, detergency, and the displacement of liquid phases through porous media on one hand, and to stabilize dispersions (including foams, froths and emulsions), or to destabilize dispersions (again including foams and emulsions) on the other hand. These in turn lead to a vast array of practical application areas which are illustrated in terms of mineral and petroleum processing, biological systems, health and personal care products, foods, and crop protection.

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2 Surfactants and their applications

In recent years, the number of non-aqueous solvents which mediate hydrocarbon–solvent interactions and promote the self-assembly of amphiphiles has been markedly increased by the reporting of over 30 ionic liquids which possess this previously unusual solvent characteristic. This new situation allows a different exploration of the molecular “solvophobic effect” and tests the current understanding of amphiphile self-assembly. Interestingly, both protic and aprotic ionic liquids support amphiphile self-assembly, indicating that it is not required for the solvents to be able to form a hydrogen bonded network. Here, the use of ionic liquids as amphiphile self-assembly media is reviewed, including micelle and liquid crystalline mesophase formation, their use as a solvent phase in microemulsions and emulsions, and the emerging field of nanostructured inorganic materials synthesis. Surfactants, lipids and block co-polymers are the focus amphiphile classes in this critical review (174 references).

Ionic liquids as amphiphile self-assembly media.

Aqueous surfactant-alcohol systems: a review

Effect of alcohol on the properties of micellar systems

From simple micelles in water, nearly spherical aggregates of amphiphilic molecules, to bicontinuous microemulsions, oil and water microheterogeneous mixtures stabilised by a surfactant film with both local and large-scale disordered structures, the world of surfactant-containing systems is fascinating. Depending on a subtle balance of attractive and repulsive interactions between molecules at interfaces, an extraordinarily rich polymorphism of aggregated structures can be observed. After summarising the basic general constraints controlling surfactant aggregation and the formation of interfaces, different structures of micelles and microemulsions are reviewed and related to interfacial film properties and the intermolecular interactions inside them.

https://iopscience.iop.org/article/10.1088/0034-4885/53/3/002/pdf

The structure of micelles and microemulsions

Micelle formation of 2 ionic surfactants (viz., sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB)) has been studied in organic solvents of various dielectric constant and intermolecular H-bonding capability (viz., n-methylacetamide (NMA), formanide (FA), dimethyl sulfoxide (ME/sub 2/SO), and n-n'dimethylformamide (DMF)), at different temperatures by conductance measurements. Delta HMDO and delta SMO, standard enthalpies and entropies of micelle formation, respectively, have been determined by studying the variation of the critical micelle concentration with temperature. Compensation plots have been obtained for both the surfactants in the above solvents. The value of slope of these plots are almost identical with each other and also with that obtained in aqueous medium. Micelle formation in these solvents has been explained on the basis of several factors such as dielectric constant of the medium, its intermolecular H-bonding capability, and also its bulk structuredness. 20 references.

Micelle formation of ionic surfactants in polar nonaqueous solvents

The effect of monohydroxy alcohols on the critical micelle concentration (CMC) of anionic and cationic surfactants have been studied by a conductometric method. The CMC was found to decrease by adding small quantities of alcohol and raised again at higher alcohol concentrations. The CMC decreasing effect has been discussed on the basis of more ordered water cavity formed around the added alcohol molecules and their increasing effect by the partition of alcohol between the micellar and the bulk phase leading to the break-down of the micelles. The effect of urea on CMC in alcohol–water mixtures has been studied and its CMC increasing effect explained.

Effect of monohydroxy alcohols and urea on the CMC of surfactants.

Growth of Sodium Dodecyl Sulfate Micelles in the Presence of n-Octylamine

Effect of electrolytes on the micellization of ionic surfactants in n-alkanol—water mixtures

Water-in-oil microemulsions were produced by mixing different combinations of the cationic surfactants cetyltrimethylammonium bromide and cetylpyridinium chloride,n-alkanes (C5–C7) and benzene as oils,n-alkylamines (C6 and C8) and cyclohexylamine as cosurfactants with water The influence of chainlength of the alkanes and amines on water solubilization behavior of these systems has been investigated The solubilization of water in a particular microemulsion is governed by the partitioning of amines among oil, water and interfacial phases, depending on the chainlength and nature of oil and amine, and their interaction with the surfactant The molar ratio of amine to surfactant at the droplet interface increased with the length of the oil chain The free energy changes accompanying cosurfactant adsorption at the interface have also been computed

H. N. Singh

Papers

Micelle formation of ionic surfactants in polar nonaqueous solvents

Effect of monohydroxy alcohols and urea on the CMC of surfactants.

Growth of Sodium Dodecyl Sulfate Micelles in the Presence of n-Octylamine

Effect of electrolytes on the micellization of ionic surfactants in n-alkanol—water mixtures

Water solubilization in microemulsions containing amines as cosurfactant