Anionic surfactants classification

Cetyltrimethylammonium bromide CH3(CH2)i5N(CH 3)381 is a typical cationic surfactant. Dissociation of this compound results in amphiphilic cations and small hydrophilic anions. This classification of surfactants is similar to the classification of strongly interacting compounds (other than surfactants) in Sections II and III into cations (Section II A), anions (Section II B) and electroneutral and zwitterionic organic compounds (Section III). The adsorption of anionic surfactants is indeed enhanced, when the adsorbent carries high positive surface charge (at low pH for materials hsted in Tables 3.1, and 3.3-3.5), and adsorption of cationic surfactants is more pronounced at high pH, and the adsoiption of nonionic surfactants is often rather insensitive to the pH. However, the mechanisms of surfactant adsorption, and experimentally observed adsorption isotherms of surfactants are very different from the compounds discussed in Sections II and III. 

The most popular classification of surfactants is based on its ionic characteristics they are either anionic, cationic, or nonionic. Since ions are normally found in aqueous fluids, ionic characteristics of surfactants are found in the hydrophilic head thus, an anionic surfactant would have negatively charged species in the hydrophilic heads. Because of the requirement of charge neutrality in an overall fluid system, an anionic surfactant would have its positive counterion within its vicinity. This counterion is subject to various ion-exchange mechanisms either with other types of counterions in the fluid or on solid surfaces. It is possible for nonionic species to be hydrophilic, because of their polar and hydrogen-bonding interactions with water molecules. 

Schemes for classifying surfactants are based upon physical properties or upon functionality. Charge is tire most prevalent physical property used in classifying surfactants. Surfactants are charged or uncharged, ionic or nonionic. Charged surfactants are furtlier classified as to whetlier tire amphipatliic portion is anionic, cationic or zwitterionic. Anotlier physical classification scheme is based upon overall size and molecular weight. Copolymeric nonionic surfactants may reach sizes corresponding to 10 000-20 000 Daltons. Physical state is anotlier important physical property, as surfactants may be obtained as crystalline solids, amoriDhous pastes or liquids under standard conditions. The number of tailgroups in a surfactant has recently become an important parameter. Many surfactants have eitlier one or two hydrocarbon tailgroups, and recent advances in surfactant science include even more complex assemblies [7, 8 and 9].

An unknown commercial detergent may contain some combination of anionic, nonionic, cationic, and possibly amphoteric surfactants, inorganic builders and fillers as weU as some minor additives. In general, the analytical scheme iacludes separation of nonsurfactant and inorganic components from the total mixture, classification of the surfactants, separation of iadividual surfactants, and quantitative determination (131). 

The classification of surfactants in common usage depends on their electrolytic dissociation, which allows the determination of the nature of the hydrophilic polar group, for example, anionic, cationic, nonionic, and amphoteric. As reported by Greek [18], the total 1988 U.S. production of surfactants consisted of 62% anionic, 10% cationic, 27% nonionic, and 1% amphoteric. 

A simple classification of surfactants based on the nature of the hydrophilic group is commonly used. Four main classes may be distinguished, namely, anionic, cationic, zwitterionic, and nonionic. A useful technical reference is McCutchen. Another useful text, by van Oss et al., gives a list of the physicochemical properties of selected anionic, cationic, and nonionic surfactants. The handbook by Porter is also a useful book for classification of surfactants. Another important class of surfactants, which has attracted considerable attention in recent years, is the polymeric type. A brief description of the various classes is given below. 

In 1993, the European Union revised its criteria for classification and labelling of substances and preparations based on their potential to cause ocular lesions [5] and in 1995 new experimental data on the irritation potential of surfactant raw materials became available. This led CESIO, once again, to review its guidance on classification and labelling of anionic and non-ionic surfactants. It resulted in the increase in several classification and labelling recommendations. These revisions, together with the classifications for quaternary ammonium compounds and fatty amines and derivatives which remained unchanged from the 1990 Report, are contained in the latest report published in January 2000 [6]. 

The octanol-water partition coefficient for surfactants can not be determined using the shake-flask or slow stirring method because of the formation of emulsions. In addition, the surfactant molecules will exist in the water phase almost exclusively as ions, whereas they will have to pair with a counter-ion in order to be dissolved in octanol. Therefore, experimental determination of K w does not characterize the partition of ionic surfactants (Tolls, 1998). On the other hand, it has been shown that the bioconcentration of anionic and non-ionic surfactants increases with increasing lipophilicity (Tolls, 1998). Tolls (1998) showed that for some surfactants, an estimated log Kow value using LOGKOW could represent the bioaccumulation potential however, for other surfactants some correction to the estimated log Kow value using the method of Roberts (1989) was required. These results illustrate that the quality of the relationship between log Kow estimates and bioconcentration depends on the class and specific type of surfactants involved. Therefore, the classification of the bioconcentration potential based on log Kow values should be used with caution. 

Classification Organic acid Formula R(OCH2CH2)nOCH2COOH, R = coconut oil fatty acids, avg. n = 6 Properties Anionic/nonionic Uses Surfactant, emulsifier in cosmetics, hair care, skin care coupling agent lime soap dispersant... 

Classification Substituted aromatic compd. Empirical C18H30O3S K Properties Anionic Toxicology TSCA listed Uses Surfactant for S/B, vinyl chloride, VDC latexes, cosmetics emulsifier in food pkg. Regulatory FDA 21CFR 178.3400 Trade Name Synonyms POLYSTEP A-15-30K [Stepan http //www.stepan.com]... 

There are fom basic classifications of textile surfactants cationic, anionic, nonionic, and amphoteric [10]. Overall, usage is about 59% anionic (25% natural soaps, 34% synthetic), 33% nonionic, 7% cationic, and 1% amphoteric [36]. Alkylphenol ethoxylate (APE) surfactants are one of the largest groups of nonionic surfactants, accounting for over 400 million pounds per year in the United States [37]. These fom categories include major product types shown in Table 7.16 [10, 31, 37, 38],... 

The role of surfactants in stabUizing emulsions, as well as the relationship between demulsifier structure and performance, has been identified for over 50 years [J9]. The classification of surfactants as well as demulsifiers is quite arbitrary, but a commonly used one is based on chemical structure [20, 21], Chemical types include nonionic, anionic, and cationic. A brief summary of the evolution in demulsifier chemistry over the years and the effective concentration range is presented in Table 1. The development of chemicals which are more surface active has allowed for reductions in the average dosages. 

Although betaines are commonly classified among amphoterics, we preferred to cover this class of surfactants in a previous topic devoted to quaternaries (Sec. H.B.3.C.). Indeed, as already explained, the classification of betaines as amphoterics is improper because these surfactants never exhibit in single anionic form. 

Besides, in the hydrophobic part, a surfactant may have homologous chains and positional isomers for example, cocoamidopropyl betaine may contain alkyl chains with a carbon pair number from 8 to 18, the majority being those with a carbon number of 12 and 14. Aromatic groups are usually bonded in alkyl chain, like in alkylphenols (nonionic) or alkyl-benzenesulfonates (anionic). Also, the hydrophilic part may contain oligomers of ethylene oxide or propylene oxide. In this article, cationic polymers have been included as a subclass of cationic surfactant based on the classification made by Richmond (1990), although many authors consider this polymer to be another ingredient of cosmetic products. Another subclass, quaternary ammonium compounds (four alkyl chains around a nitrogen atom) will be frequently mentioned components. 

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