Surfactants anionic-active

The action of both herbicides can be increased by the addition of nonionic surfactants. Anion-active surfactants are incompatible with bipyridylium herbicides. 

The next sections deal with four types of surfactants anionic-active, cationic-active, amphoteric and non-ionic. More information on surfactants is to be found in Sect. 18.3, in Martindale and other literature [3,4,32]. Table 23.13 gives an overview of the main surfactants that are used in small-scale preparation. 

Sodium dodecyl sulfate is the universal analytical standard for the determination of anionic and cationic active matter. It is used to determine the analytical concentration factor of the cationic surfactant in the titration of anionic active matter and as titrant to determine the cationic active matter. 

The types of analyses discussed in this section can be divided into two groups active matter and impurities. Several methods assess the anionic surfactant (active matter) content of the AOS product. These are particularly important since detergent performance is directly related to surfactant concentration. The different types of anionic active material are identified and quantified. 

The experiments indicated that foam films rupture at pressures lower than nmax is not due to occasional reasons. Critical pressure pcr was observed with different types of films (common foam, CBF and NBF) stabilised with various kinds of surfactants [171,303]. Similar effect has been observed by Black and Herrington [261] who studied films stabilised with three anion-active surfactants. However, details on the critical pressure of film rupture will not be discussed here, since a satisfactory theoretical explanation of this effect has not been proposed so far. There are some hypothesis on the matter. Nevertheless, this parameter has been successfully employed in clarifying the role of foam films in foam stability (see Chapter 7). No doubt, this parameter provides information about the stability of the different types of foam films and is awaiting its qualitative interpretation. 

Anionic Surfactants. Anionic surfactants are surface-active agents in which the hydrophobic portion is connected to an anion or negatively charged ion. In an... 

This equation contains a single activity coefficient. However, as the activity of the surfactant anion is dominated by its interaction with the abundantly present Na ions and hence virtually constant, dlny. = 0. Hence,... 

Chlorhexidine salts are cationic in solution and are therefore incompatible with soaps and other anionic materials. Chlorhexidine salts are compatible with most cationic and nonionic surfactants, but in high concentrations of surfactant chlorhexidine activity can be substantially reduced owing to micellar binding. 

Wu, S.H. and Pendleton, P. (2001). Adsorption of anionic surfactant by activated carbon effect of surface chemistry, ionic strength and hydrophobicity. J. Colloid Interface Sci., 243, 306-15. 

Of the four types of synthetic surfactants, anionic, cationic, amphoteric, and nonionic, the anionic surfactants provide maximum lather and hence are used as major components in liquid products. The active ingredients used in the major brands of liquid soaps are described by Dyer and Hassapis [6],... 

With respect to the properties of polar groups, surfactants can be subdivided into ionic (cation- and anion-active, ampholytic, and zwitterionic) and nonionic surfactants. If the effect produced by the polar group of the surfactant molecule is more significant than that of the lipophilic group, this substance is soluble in water. It is less surface active as compared to any substance characterized by an optimum balance between the activities of hydrophilic and lipophilic groups. Similar conclusions can be drawn also with respect to the solubility in oil here, the role of the lipophilic group is determining. Clearly, the efficiency of a surfactant is not determined solely by the amphiphilicity, but depends on the hydrophilic/lipophilic balance (HLB) characteristic for this compound. Therefore, this balance is an important characteristic of both the surfactant and the interface. 

Surfactant Surface active agent is a compound that alters the surface tension of a hquid in which it is dissolved. AH surfectants have large polar molecules. One end of the molecule is soluble in water (due to carboxyl, sulphate, hydroxyl, or srJphonate groups) and the other end is readily soluble in oils (organic groups). Synthetic sur ctants are of three types anionic, cationic and nonionic. 

Amphoteric surfactants are characterized by a molecular structure containing two different fnnc-tional groups, with anionic and cationic characters, respectively [19]. Most amphoteric surfactants are able to behave like cationic snrfactants in acidic medinm, and like anionic surfactants in alkaline medium. However, betaines are different in that they cannot be forced to assume anionic active behavior through an increase in the pH valne [20,21]. Fignre 12.7 shows strnctnres of the most widely nsed amphoteric surfactants, as prodnced, in dependence of the pH valne. 

Hydrophilic creams are preferably formulated with combinations of emulsifying agents (mixed layer emulsifying agents or emulsifying agent complexes, see Sect. 18.4.3). For examples of o/w surfactants see Sect. 12.5.4. Generally hydrophilic creams may be anionic-active or non-ionic-active. Because of incompatibilities of active substances with anionic or non-ionic-active surfactants mixtures of these types of emulsiflers have to be avoided. The lipophilic excipients improve the consistency of the cream. These may be hydrocarbons such as white soft paraffin or waxes such as decyl oleate. 

If the active has been converted to the free acid by passage through a strongly acidic cation exchanger, retained on a weak free base resin and then eluted with ammonia, the eluate contains the ammonium salts of any non-surfactant anions that were present in the sample. 

Active over the entire usable pH range (pH 2 through pH 12). Outstanding compatibility with acids, alkalis, hard water, soap lathers, electrolytes, and surfactants (anionic, cationic, nonionic, and amphoteric). 

All dispersing agents are surface active and they can be simple surfactants (anionic, cationic, zwitterionic or nonionic), polymers or polyelectrolytes. The dispersing agent should be soluble (or at least dispersible) in the liquid medium and it should adsorb at the solid/liquid interface. 

Molecules composed of hydrophilic as well as of hydrophobic parts are called amphiphilic, soaps are simple examples. In strongly polar (e.g., water) or apolar solvents (e.g., alkanes) their solubility as monodisperse molecules is small. The contact of the respective lyophobic moieties to the solvent can be avoided by accumulation at the interfaces of the solution, see Figure 14.1. The interfacial properties of solutions are determined distinctly by dissolved amphiphilic matter which for that reason is termed surfactant (surface active agent). Typical examples of ionic (cationic or anionic), zwitter-ionic, and nonionic surfactants of low molecular weight are sketched in Figure 14.2. 

Anionic Surfactants Anionic surfactants are surface-active agents in which the hydro-phobic portion is connected to an anion or negatively charged ion. In an aqueous medium, an anionic surfactant dissociates into a positively charged cation and a negatively charged anion. The latter is the carrier of the surface-active properties. Typical examples are the alcohol sulfates and the ester sulfonates. 

Amphoterics are usually used in conjunction with other surfactants (anionics or nonionics) to boost desired properties such as foam or detergency. Since the optimal surface activity of amphoterics takes place around neutral pH, they are particularly appreciated in personal care products (shower gels, foam baths, shampoos, etc.) for their mildness and skin compatibility. 

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