Surfactants polar headgroups, types

The class of compoimds most extensively studied at liquid surfaces by VSF is the alkyl ionic surfactants. The simplest type of these surfactants consists of a charged polar headgroup and a long hydrocarbon chain and represents typical surfactants used in commercial products and industrial processes. In a typical soap or detergent solution, if the concentration of surfactant is high enough, the surfactant molecules form micelles... 

The basic mode of mesophase formation is as described above for CTAB. However, as one might expect, things are not quite so straightforward and there are various types of mesophase which can be formed from various types of surfactant. The surfactant structure can be varied so that fluorocarbon chains can be employed in place of the hydrocarbon variety, while anionic (e. g. -SOa") and the neutral (e.g. -(0CH2CH2) -0H) polar headgroups are often used. These surfactants can then form a variety of different mesophases as a function of (mainly) concentration in the solvent of choice (normally water). These phases are the lamellar (L ) phase, a simple bilayer phase, and variations on the cubic (li, I2, Vi, V2) and hexagonal (H, H2) phases. For these last phases, the subscript 1 implied a normal phase as found in a water-rich system, while the subscript 2 implied a reversed phase as found in an oil-rich system. For the cubic phases, the letter F implied a micellar phase (e. g. 

Not only do surfactants and cosurfactants lower the interfacial tension, but also their molecular structures affect the curvature of the interface as shown schematically in Fig. 3. The hydrocarbon chains are rather closely packed (about 0.25 nm per chain) they repel one another sideways and as a result have a tendency to bend the interface around the water side. The counterions of the ionic headgroups also repel one another sideways and thus tend to curve the interface around the oil side. The bullQ polar groups of nonionic surfactants have a similar effect. So we understand qualitatively that more cosurfactant promotes W/O rather than O/W microemulsions. More electrolyte compresses the double layer, diminishes the sideways pressure of the double layer, and also promotes W/O microemulsions. The polar groups of PEO nonionics become more compact (less soluble) at higher temperatures, and so with this type of surfactants high temperature leads to W/O microemulsions. 

Surfactants, both ionic and neutral, are also commonly characterized qualitatively by their HLB values, related to the hydrophobicity of their tails that increases with the alkyl chain length or the number of carbons in the tail versus the polarities or water solublities of the various headgroup and counterion types. The hydrophilicities of ionic surfactants with different counterions are difficult to compare... 

The typical surface-active or surfactant molecule consists of at least one polar hydrophilic part and one apolar hydrophobic part, such as a hydrocarbon or fluorocarbon chain. Although there is normally only one headgroup per surfactant molecule, there are frequently several nonpolar tails. These can be linear or branched, the most common being single and linear. Because of the coexistence of two opposite types of behavior inside the same molecule, surfactants can build different submicroscopic aggregates in water that can organize themselves into various supramolecular structures of macroscopic dimensions and different properties. The variety of supramolecules ranges from micelles to liquid crystalline... 

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