Amphoteric surfactants classes

Anionic surfactants are the most commonly used class of surfactant. Anionic surfactants include sulfates such as sodium alkylsulfate and the homologous ethoxylated versions and sulfonates, eg, sodium alkylglycerol ether sulfonate and sodium cocoyl isethionate. Nonionic surfactants are commonly used at low levels ( 1 2%) to reduce soap scum formation of the product, especially in hard water. These nonionic surfactants are usually ethoxylated fatty materials, such as H0CH2CH20(CH2CH20) R. These are commonly based on triglycerides or fatty alcohols. Amphoteric surfactants, such as cocamidopropyl betaine and cocoamphoacetate, are more recent surfactants in the bar soap area and are typically used at low levels (<2%) as secondary surfactants. These materials can have a dramatic impact on both the lathering and mildness of products (26). 

A surfactant can be grouped in one of the four classes - anionic, nonionic, cationic and amphoteric surfactants, depending on what charge is present in the chain-carrying hydrophilic portion of the molecule after dissociation in aqueous solution. Tab. 4.1 shows examples of surfactants most commonly used for detergents. 

Even if this class covers the smallest market segment, amphoteric surfactants still remain useful because of their unique properties, which justifies their comparably high manufacturing costs. Since they have partial anionic and cationic character, they can be compatible, under specific conditions, with both anionic and cationic surfactants. They can function in acid or basic pH systems and, at their isoelectric point, they exhibit special behaviour. Many amphoteric surfactants demonstrate exceptional foaming and detergency properties combined with antistatic effects. 

Cocamidopropyl betaine (Table 1.4) is the most prominent representative of the class of amphoteric surfactants. Due to the synergism with other surfactants and its gentleness to the skin and mucous membranes, cocamidopropyl betaine performs well in shampoo and cosmetics where its dosage lies in the order of 1-5% [27]. 

A broad range of information pertaining to the toxicity of several classes of surfactants including anionic (linear alkylbenzene sulfonates (LAS), alkylether sulfates (AES), alkyl sulfates (AS), non-ionic (alkylphenol ethoxylates (APEO)), cationic (ditallow dimethyl ammonium chloride (DTDMAC)—a group of quaternary ammonium salts of distearyl ammonium chloride (DSDMAC)) and amphoteric surfactants (alkyl-betaines) is available. Several reviews of the scientific literature have been published [3-5,20]. 

Two major classes of amphoteric surfactants are derived from fatty alkyl hydroxyethyl imidazolines which, in turn, are produced from fatty acids and low molecular weight amines. Because fatty acids are fairly economic, the imidazoline derived amphoacetates tend to be less expensive than the iminodipropionates discussed above. Most imidazoline derived... 

The other major class of fatty imidazoline derived amphoteric surfactants is the amphopropionates. Again, the ampho portion of the name indicates that they are derived from imidazolines but, rather than being alkylated with sodium chloroacetate, they are carboxy-lated with an acrylate via the Michael reaction. A primary or secondary amine is added across the double bond of the acrylate to yield the beta-alanine derivative. 

Depending on the nature of the hydrophilic groups of surfactants, they can be divided into anionic, nonionic, cationic, and amphoteric surfactants. The last-mentioned class only plays a minor role with respect to domestic and industrial applications and practically no methods for the environmental analysis of amphoteric surfactants have been published so far. 

This class of surfactant includes those that cany both positive and negative diarges. Depending on the pH of the preparation, this group behaves as a cationic, anionic, or nonionic species. In the cosmetics held, these surfactants are frequently applied in skin or hair formulations as relatively mild detergents. They are also used for their capacity for reducing the irritation of anionic surfactants. These surfactants are commonly accepted to be noninitant to the eyes and have consequently been used in baby shampoos. Amphoteric surfactants are very much used in cosmetics, but they are not found in the different pharmacopoeia studied here. 

Anionics are the largest class of surfactants in terms of volume, and include the work-horse surfactants, linear alkylbenzene sulfonate (LAS), alcohol sulfate (AS) and alcohol ether (or ethoxy) sulfate (AES). Cationic surfactants generally include various quaternary salts, used predominantly as fabric conditioners ( fabric softeners ), anti-static agents and anti-microbial agents. Amphoteric surfactants represent the smallest class of surfactants, and generally are used when solubility, mildness and compatibility issues are important. 

With regard to bioconcentration, it is important that surfactants are characterized by combining a lipophilic and a hydrophilic moiety in the same molecule. This is true for all four classes, namely anionic, nonionic, cationic and amphoteric surfactants. Although these classes possess quite different hydrophilic groups, the lipophilic part usually consists of an alkyl chain or alkyl chains of different lengths. There is some evidence that the lipophilic groups of surfactants are metabolized after uptake by aquatic invertebrate species (Daphnia and Chironomus) and fish. 

The solubilizing power of amphoteric surfactants has not been as widely studied, or at least as widely reported, as that for the simpler ionic and nonionic materials. However, the available data indicate that they lie somewhere between the extremes in solubilizing capacity the exact results are probably more sensitive to the nature of the additive than those for the other classes of surfactants. 

The formulation class (tooth paste, shampoo, fabric softener, etc.) provides basic information about the components present. Standard shampoo formulations contain two types of surfactants (either two anionic or one anionic and one amphoteric surfactant) foam booster (nonionic surfactant) conditioner, viscosity improver, opacifier, dye, perfume, chelate, and preservatives. Normally, formulated products are available as liquid, solid, emulsion, dispersion, etc, with a great number of components (in some cosmetic products there may be 20 components) and some of them, such as the preservatives, are found at low concentrations. 

Amphoteric surfactants are divided into two groups based on their response to pH. One class of compounds that contain carboxylated imidazoles and A-alkyl betaines are zwitterionic at pHs at, and above, their isoelectric points and cationic at lower pHs. Sulfobetaines and phosphobetaines, on the other hand, exhibit zwitterionic characteristics as the anionic portion is dissociated at all pHs. Although the former are the major ingredients in many baby shampoos or those products that provide mildness, they also function as foam and viscosity enhancers when utilized as secondary surfactants, having good water solubility over a wide pH range. ° ... 

Amphoteric surfactants can be subdivided into three major classes ... 

Carboxy amphoteric surfactants based on fatty alkyl imidazolines (imidazolinium surfactants) make up a large part of the amphoteric surfactants. Materials of this surfactant class are based on the imidazolines obtained by the condensation of fatty acids or their esters with aminoethyl ethanol amine. 

Amphoteric surfactants are a class of chemicals whose functionality and utility to the industry is showing definite growth. As a class of surfactants, they are safe, both functional and with low irritation potentials for consumer products and, consequently, are finding increased use in personal products. The wide range of chemistries that are encompassed by this class of surfactant afford product development chemists the opportunity to tailor the performance of their products for specific applications. This is evident by the broad range of industries interested in these technologies. 

The four main surfactant classes include anionics, cationics, nonionics, and amphoterics or zwitte-rionics. Within each of the general classes of surfactants, there are a broad range of variants, which are summarized in the following sections. 

Carboxyamphoteric surfactants based on fatty alkyl imidazolines ( imidazolinium surfactants) make up a large part of the amphoteric surfactants. The very divergent interpretation of their chemical structure is partly attributable to little-developed analytical procedures in the past, but is also a consequence of special processing methods by different manufacturers. Materials of this surfactant class are based on the imidazolines obtained by the condensation of fatty acids, or their esters, with AEEA. In Figures 12.4 and 12.5, a summary of the synthesis of amphoteric surfactants based on imidazolines [4,8] is presented. 

These surfactant classes are a subset of those used in cleaning applications, and there are classes that are noticeably absent from the list above, such as alcohol sulfates, salts of fatty acids (soaps), alkanolamides, aliphatic sulfonates, betaines (amphoterics), methyl ester sulfonates and the relatively new alkyl polyglycosides. All of these have seen various applications in the petroleum industry, but perhaps lesser importance in EOR. Cost, availability and performance are the obvious issues in determining the potential use of surfactants in EOR. 

The cationic charge on a polymer affects its behavior considerably when surfactants are included in formulations. Cationic polymers (a member of the broader class of polymers termed polyelectrolytes) usually interact strongly with anionic surfactants, weakly with cationic surfactants, and unpredictably with nonionic and amphoteric surfactants (14,167-169). Anionic surfactant binds to cationic polymers at concentrations well below the critical micelle concentration (cmc). The low surfactant concentration where polymer and surfactant begin to interact is known as the critical aggregation concentration (cag). 

Zwitterionic or amphoteric surfactants are an important class of molecules owing to their particular properties such as tolerance to hard water, strong electrolytes, oxidizing and reducing agents, low toxicity, and compatibility with other amphiphiles. 

According to their physical-chemical nature, the surfactants can be subdivided into ionic (about 70% of all surfactants manufactured) and nonionic. In nonionic surfactants, the polar part mainly consists of multiple ethylene oxide units, -(CH2CH20) - while ionic surfactants can be subdivided into three large classes based on the charge of their polar group, that is, anionic, cationic, and zwitterionic (amphoteric) surfactants. 

Amphoteric surfactants have both anionic and cationic groups in the same molecule, and the pH value of the solution determines the predominant electrical charge on the surfactant. Examples of this class are aminocarboxylic acids and betaines. 

Surfactants are divided into five major classes soaps, anlonlC, non-ionie, cationic, and amphoteric surfactants. Each contains a hydrocarbon tail and a polar head. Typical surfactants of each class are represented below ... 

A further class of amphoteric surfactants, which are related to quaternary ammonium compounds, are the alkylbetaines. These are obtained by reacting an alkyldimethylamine with sodium chloroacetate. 

Some types of amphoteric surfactants (to be discussed below) in which the nitrogen is covalently bound to a group containing an anionic (e.g., -CH2CH2S03") or potentially anionic (e.g., -COOH) functionality are also classed as cationic in some publications however, under the classification scheme employed in this work, such materials are covered in a separate category. The examples above represent the simplest types of cationic surfactants. Many modem examples contain much more complex linkages however, the basic principles remain unchanged. 

ImidazoUne-derived surfactants represent one of the most commercially important classes of amphoteric surfactants. Although mentioned in the patent and surfactant... 

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