Anionic surfactants definition

Amphiphilic compounds as surfactants, 21 Amphoteric surfactant, definition, 386 Analysis speed, importance, 125 Anionic surfactants definition, 387... 

This definition of surface lipid by Koch probably provides a high estimate for surface hair lipid. Another definition is the amount of lipid removed by a double application of an anionic surfactant. This latter definition probably provides a more realistic estimate for surface hair lipid. However, if one accepts this latter definition, then the amount of lipid left in hair after shampooing represents internal lipid and may be estimated by solvent extraction (ethanol) after shampooing. 

Definition Lactic acid salt of isostearamidopropyl dimethylamine Empirical C26H54N2O4 Formula C23H48N2O C3H6O3 Properties M.w. 458.73 compat. with anionic surfactants... 

Nonionics can function as cosurfactants in microemulsions. This cosurfactant role, which can also be performed by short-chain alcohols or glycol ethers, can make it possible to form microemulsions or other phases from anionic surfactant systems that would otherwise be unreachable in a pure anionic system. By one definition, a microemulsion system is one that achieves a zero or close-to-zero curvature [108]. This is easily achievable in nonionic systems, but very difficult in pure anionic surfactant systems due to the head group repulsions. Mixing the nonionic with the anionic makes these types of systems, which sometimes have greater cleaning ability, easily accomplished. 

Another important point, and one of fundamental significance, is that above the isoelectric point, although no precipitation is observed with added SDS, definite indications of interaction can still be obtained see, for example, the surface tension data for gelatin/ SDS presented below, calorimetric data for BSA/SDS (128), and other information to be given later. This means that proteins, like many HM-polyions, are able to interact with ionic surfactants against an unfavorable (overall) electrical gradient. For this reason many studies involving anionic surfactants have been executed above the i.e.p. of the protein, as illustrated below. 

Reference has already been made to the interesting finding by Laurent and Scott (65) that precipitation of various polyanion/cationic surfactant systems can be totally inhibited by the addition of a sufficient amount of simple salt. This work allowed the definition of a critical electrolyte concentration (c.e.c.), which was found to vary from system to system. Clearly, electrostatic screening effects are again involved. This phenomenon has been confirmed and examined in some detail by Lindman and co-workers (see next section). Less work has been carried out in this respect on polycation/anionic surfactant systems and, at least in some systems involving cationic cellulosic polymer/SDS combinations, resolubilization by salt addition was found not to be facile (59,103). 

H-NMR spectroscopy can provide information on the environment of the fluorinated surfactant in the micelle. The high sensitivity of the H nucleus is a definite advantage. Monduzzi et al. [118] utilized the Fourier transform pulsed-gradient spin-echo (FTPGSE) H-NMR technique to determine the self-diffusion coefficients of water in W/0 (water-in-oil) microemulsions containing perfluo-ropolyether (PFPE) oils and an anionic surfactant with a PFPE hydrophobe. The self-diffusion data provided quantitative information on the amount of water in the composition range where continuous water coexists with water in droplets. 

A more efficient method of isolating anionic surfactants is extraction as part of an ion pair (33). An inorganic salt is added to decrease the solubility of the ion pair in the aqueous phase. Sometimes, the methylene blue spectrophotometric method described in Chapter 12 is used as the cleanup step. This permits the analyst to estimate the amount of surfactant isolated before proceeding with more definitive analytical techniques. Methylene blue may be removed from the surfactant extract by passage through a cation exchange column (56). If concentration is performed by liquid-liquid extraction of the ion pair with an alkyl quaternary compound, the UV spectrum of the ion pair is identical to that of LAS alone (55). 

The two distinctive affinities in the surfactant molecule mentioned above serve as the basis for the commonly accepted definition of surfactant groups. According to the charge of their hydrophilic moiety, surfactants can be classified into four categories anionic, non-ionic, cationic and amphoteric. 

Nonionic surfactants are amphiphilic compounds the lyophilic (in particular hydrophilic) part of which does not dissociate into ions and hence has no charge. However, there are nonionics, for example such as tertiary amine oxides, which are able to acquire a charge depending on the pH value. Even polyethers, such as polyethylene oxides, are protonated under acidic conditions and exist in cationic form. Long-chain carboxylic acids are nonionic under neutral and acidic conditions whereas they are anionics under basic conditions. So, the more accurate definition is as follows nonionics are surfactants that have no charge in the predominant working range of pH. The main part of nonionics can be classified into alcohols, polyethers, esters, or their combinations. 

For shampoos, shaving foams and tooth pastes, high stability and definite foam structure is one of the main factors determining the commercial value of the product. In this connection, conventional shampoos include anionics (ammonium or triethanolamine salts of alkylsulphates mixed with alkylolamides of natural fatty acids, e.g. coconut oil acids, as well as amphoteric surfactants and hydrolysed proteins. Detailed patent data on the formulations are given in [80, 110] and other reviews. 

Quaternary alkylammonium salts, used as flow reverser additives in the separation of small anions, will fall technically into the EKC definition, since the surfactant micellization is anticipated due to the electrolyte ionic strength in which the separation is conducted vide section on small ions analysis). 

Steroid-Based Anion Conzplexation Agents, p. 1365 Supramolecular Chemistry Definition, p. 1401 Supramolecular Stabilization, p. 1453 Surfactants, Part I Fundamentals, p. 1458 Surfactants, Part 11 Applications, p. 1470 van der Waals Forces, p. 1550 Weak Hydrogen Bonds, p. 1576... 

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