Surfactants double-tailed

Cationic surfactants may be used [94] and the effect of salinity and valence of electrolyte on charged systems has been investigated [95-98]. The phospholipid lecithin can also produce microemulsions when combined with an alcohol cosolvent [99]. Microemulsions formed with a double-tailed surfactant such as Aerosol OT (AOT) do not require a cosurfactant for stability (see, for instance. Refs. 100, 101). Morphological hysteresis has been observed in the inversion process and the formation of stable mixtures of microemulsion indicated [102]. 

While most vesicles are formed from double-tail amphiphiles such as lipids, they can also be made from some single chain fatty acids [73], surfactant-cosurfactant mixtures [71], and bola (two-headed) amphiphiles [74]. In addition to the more common spherical shells, tubular vesicles have been observed in DMPC-alcohol mixtures [70]. Polymerizable lipids allow photo- or chemical polymerization that can sometimes stabilize the vesicle [65] however, the structural change in the bilayer on polymerization can cause giant vesicles to bud into smaller shells [76]. Multivesicular liposomes are collections of hundreds of bilayer enclosed water-filled compartments that are suitable for localized drug delivery [77]. The structures of these water-in-water vesicles resemble those of foams (see Section XIV-7) with the polyhedral structure persisting down to molecular dimensions as shown in Fig. XV-11. 

This range yields more highly tmncated cones. The main mesophase stmcture obtained from these units is a flexible bilayer such as that fonned in vesicles and liposomes. These arrangements are often obtained from doublechain surfactants such as lecithin, double tailed cationic surfactants and AOT. 

The idealized reverse micelle sketched in figure C2.3.1 is an aggregate of a double-tail surfactant. In such systems the solvent is more compatible with the lyophobic part of the surfactant than with the headgroup. This preference... 

When anionic and cationic surfactants are mixed they strongly interact, and it could even be said that they almost react to produce a catanionic species, which is essentially a new surfactant, in which the two hydrophilic groups have merged into a nonionic or a somehow amphoteric head attached to a double tail. The first consequence is that the new daughter species has... 

Figure 5.2 Top-diagramatic representation of a detergent molecule, (a) Single tailed (b) double tailed (c) zwitterionic (d) bolamphiphilic. Bottom - different types of surfactant aggregates in solution (A) monolayer (B) bilayer (C) liquid-crystallin phase lamellar (D) normal micelles (E) cylindrical micelles (hexagonal) (F) vesicles (liposomes) (G) reversed micelles.

Why do biological membranes and bilayers usually consist of double-tailed surfactants ... 

Generally, vesicles are prepared from double-tailed surfactants, and a simple single-tailed surfactant cannot form vesicles due to its relatively large hy-... 

Cubic strut phases are common in the phase diagrams of two-tailed surfactants. These surfactants have a relatively high value of the vfaolc parameter, because the volume-to-length ratio v/i(. of the double tail is twice that of a single tail. A high value of v/aoic is consistent with the formation of type II bicontinuous and other inverse phases, such as the inverse hexagonal phase in Fig. 12-24. 

Figure 29 Vesicles made of the double-tailed surfactant (33) and containing in the internal water pool the quinolinium derivative (35) are destroyed by acetylcholinesterase, very probably leading to the formation of micelles made of (34) and n-hexadecanol. In the process, (35) is also released and cleaved by the enzyme [98]...

Hirasaki et al. (2008) demonstrated an alternative to the use of alcohol by blending two dissimilar surfactants a branched alkoxylated sulfate and a double-tailed, internal olefin sulfonate. The presence of cosolvent affects the effective salinity and causes a shift in phase boundaries. Alcohol is an organic compound with a functional group of -OH. In aqueous solutions, the hydrogen can become detached, producing slightly acidic solutions. Alcohols with short... 

The controlled introduction of two lipophilic alkyl chains into mannuronate monomers represents a convenient way of producing double-tailed surfactants (Scheme 6). Indeed, the incorporation of longer hydrophobic alkyl chains than the two butyl groups brings a more amphiphilic character to the glycosides. 

Double-tailed ester-type surfactants 6a-c, f, g and uronamides 10c, f, g were studied as to their properties as emulsifying agents. Three systems were studied sunflower oil-water, paraffin oil (Marcol 82)-water, and capric/caprylic triglycerides (Oleon)-water. In order to determine the w/o or o/w type of emulsions formed in the presence of the surfactants, the drop-dilution method was used. To a small portion of the emulsicMi (surfactant/water/oil 5/47.5/47.5 in weight) placed oti a slide, a drop of water with a pin point is added and stirred slightly. If the water blends with the emulsion, it is an oil-in-water emulsion, but if oil blends with the outside phase it is a water-in-oil emulsion. As indicated in Table 5, ester-type and amide-type compounds 6a-c and 10c, based on C8 to C12 fatty alcohols and amines, are able to form o/w emulsions whereas surfactants 6f, g and lOf, g composed of stearic (Cl8) or oleic (C18 l) alkyl chains exhibit w/o emulsions. 

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