Amphoteric surfactants characteristics

Many of the surfactants made from ethyleneamines contain the imidazoline stmcture or are prepared through an imidazoline intermediate. Various 2-alkyl-imidazolines and their salts prepared mainly from EDA or monoethoxylated EDA are reported to have good foaming properties (292—295). Ethyleneamine-based imida zolines are also important intermediates for surfactants used in shampoos by virtue of their mildness and good foaming characteristics. 2- Alkyl imidazolines made from DETA or monoethoxylated EDA and fatty acids or their methyl esters are the principal commercial intermediates (296—298). They are converted into shampoo surfactants commonly by reaction with one or two moles of sodium chloroacetate to yield amphoteric surfactants (299—301). The ease with which the imidazoline intermediates are hydrolyzed leads to arnidoamine-type stmctures when these derivatives are prepared under aqueous alkaline conditions. However, reaction of the imidazoline under anhydrous conditions with acryflc acid [79-10-7] to make salt-free, amphoteric products, leaves the imidazoline stmcture essentially intact. Certain polyamine derivatives also function as water-in-oil or od-in-water emulsifiers. These include the products of a reaction between DETA, TETA, or TEPA and fatty acids (302) or oxidized hydrocarbon wax (303). The amidoamine made from lauric acid [143-07-7] and DETA mono- and bis(2-ethylhexyl) phosphate is a very effective water-in-od emulsifier (304). 

Amphoteric surfactants have two or more functional groups which, depending on the conditions of the medium, can be ionised in aqueous solutions to give the compound the characteristics of either an anionic... 

Although these surfactants represent less than 1% of the U.S. production of surfactants, the market use is increasing dramatically because of their unique properties [353]. Of particular importance is the synergistic effect that amphoteric surfactants have when used in conjunction with other types of surfactants. The non-eye-stinging characteristic of these compounds has been responsible for the upsurge in the baby shampoo market over time [354,355]. 

The main characteristics of amphoteric surfactants is their dependence on the pH of the solution in which they are dissolved. In acid solutions, the molecule acquires a positive charge and it behaves like a cationic, whereas in alkaline solutions they become negatively charged and behave like an anionic. A specific pH can be defined at which both ionic groups show equal ionization (the isoelectric point of the molecule). 

Amphoteric surfactants. These compounds have the characteristics of both anionic detergents and cationic fabric softeners. They tend to work best at neutral pH, and are found in shampoos, skin cleaners, and carpet shampoos. They are very stable in strong acidic conditions and are favorably used with hydrofluoric acid. For example, compounds of alkyl-betain or alkylsulfobetaine type possess both anionic and cationic groups in the same molecule even in aqueous solution. These surfactants are rarely employed in laundry detergents because of their high costs [3, 4]. 

Lines 1 and 2 in Fig. 3.60 extend over the region characteristic for non-ionic or amphoteric surfactants (except for the oxyethylated ones), and correspond to AG h =-(2.9-t-3.3) kJ/moI. Lines 3 and 4 confine the region of ionic surfactants, yielding the values AG°h, = -(2.7-1-3.8) kJ/mol. These values of the increments are approximately 10% larger than those calculated for these surfactants in the previous sections. This inconsistency is possibly due to the fact that the AG value is not exactly equal to zero (as also the difference AG, ... 

Broad pH surfactant compatibility characteristics have contributed to greater usage of amphoteric surfactants in a variety of leave-on cosmetic and skin treatment... 

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. ° ... 

The variety and range of amphoteric surfactant types are quite large. The following are the characteristic properties that amphoteric surfactants have in common [3] ... 

Broad pH surfactant compatibility characteristics have contributed to greater usage of amphoteric surfactants in a variety of leave-on cosmetic and skin treatment products. These include alpha hydroxy acid treatment creams, skin desquamation aids, cleansing gels, and massage creams. Excellent skin... 

Amphoteric surfactants comprise a broad range of compounds, which display nonionic, cationic, or even anionic tendencies depending on pH or in-use conditions. Betaines, imadazoline-derived amphoacetates, alkylamino propionates, and glycinates are generally included in this category. Amine oxides, which may exhibit nonionic or cationic characteristics depending on pH conditions, are also included in this category. 

This amphoteric surfactant, 0-oleoyl-L-homoserine, could be expected to have some characteristic properties different from those of nonionic food emulsifiers, such as monoglycerides and sugar esters. It may be safe for humans after digestion by pancreatic lipase, for two reasons (1) O-acyl-L-homo-serine is synthesized by an enzymatic process and can be hydrolyzed into fatty acids and L-homoserine by the digestive organs (2) L-homoserine is a naturally occurring amino acid and is distributed in plants, especially in germinating pea seeds [97],... 

A characteristic example in the field of cosmetics is the separation and determination of surfactants in shampoos, which contain various combinations of anionic, cationic, nonionic, and amphoteric surfactants. The surfactant combination is designed to influence the essential characteristics of the shampoo cleansing, foam, conditioning, and viscosity. Laurylether sulfates and alkylben-zene sulfonates are common anionic surfeictants used in shampoos to provide lather and cleansing. The only required sample preparation step is the dilution of the product to be analyzed in deionized water and subsequent membrane filtration (0.45 pm) prior to injection. Figure 10.200 illustrates the gradient... 

Table 4 Performance Characteristics and Application of Cationic and Amphoteric Surfactants in Personal Care Products...

Amphoteric surfactants by definition are chimeric, exhibiting anionic character in alkaline solution, nonionic character near their isoelectric point, and cationic character in acidic solution [73]. As a result of their complex charge characteristics, their interactions with interfaces must be examined iudividually and as a function of pH. For example, the adsorption of alkyl betaines firom solution onto wool keratin is much greater at acidic than alkalide pH values. Although amphoteric surfactants are used extensively to improve the cosmetic attributes of many consmner products [74], their interactions with skin have received little attention. 

Potentiometric titration with HCl gives a characteristic value proportional to the content of amphoteric surfactant (1,10,11). In some cases, solvent systems have been optimized so that acid-base titration is suitable for assay of the product, as described below for characterization of alkylbetaines (12). 

The variable electronic characteristics of the amphoteric surfactants also make them useful in textile applications where antistatic and softening properties under various conditions and on different fabric types are advantageous. Treatment of various metal surfaces is also facilitated by the ambivalent nature of such materials, leading to their use in metal treating and finishing products. 

As mentioned above, the betaine surfactants can be considered to be special members of the ring-opened, imidazoline surfactants. However, they do not exhibit many of the characteristics of other amphoteric surfactants, especially with regard to their solubility and electrical nature in alkaline solution. Even at high pH, the betaines do not acquire any significant anionic character, and they appear to... 

The foam-holding characteristics of foam from surfactants in oil field jobs can be tailored by adding an imidazoline-based amphoacetate surfactant. Amphoacetates are a special class of amphoteric tensides (Figure 16-1). Imidazoles, such as 2-heptylimidazoline, are reacted with fatty acids under the ring opening. For alkylation, the imidazoline is reacted with, for example, chloroacetate [493]. 

Surfactant has a similar amphoteric structure as lipid, which makes it possible to form a stable membrane the same as a lipid membrane and can be used to embed proteins. A surfactant membrane has many characteristics similar to those of a biomembrane, so that it can retain the bioactivities of proteins well. The process of preparing a sur-factant/protein-modified electrode is simple and viable. There are usually two methods... 

From the ESI-FIA-MS(+) spectrum in Fig. 2.5.10(b), the amphoteric amine oxide surfactants ([M]+ ions at m/z 230, 258 and 286) and their dimeric ions ([2M - H]+ at m/z 459 and 487 (230 combined with 258)) could be recognised. The identity of the amine oxides was confirmed by recording product ions of the [M]+ ion at m/z 230 before the parent ion scan of fragment m/z 58 and vice versa was recorded for confirmation. This spectrum contained the A m/z 28 equally spaced characteristic amine oxide homologue ions at m/z 230, 258 and 286. 

This ESI(+) TIC, however, is dominated by strong and broad signals that eluted between 17 and 31 min, neither observable under APCI(+/—) nor ESI(-) conditions. Even under gradient RP-C18 conditions a strong tailing effect was observed while isocratic RP-C18 failed. The information obtained by ESI—LC—MS(+) was that the compounds could be ionised in the form of [M]+ ions at m/z 230, 258 and 286. ESI-LC-MS-MS(+) resulted in product ion spectra which, by means of a MS-MS library, were found to be characteristic for the amphoteric amine oxide surfactants. These compounds not yet observed in household formulations will be presented later on with the RIC of LC separation (cf. Fig. 2.5.11(d)). After identification as amine oxides, the separation and detection of this compound mixture now could be achieved by an isocratic elution using a PLRP-column and methane sulfonic acid and ESI(+) ionisation with the result of sharp signals (RT = 4-6 min) as presented in Fig. 2.5.11(d). 

Is an amphoteric detergent and surfactant possessing both anionic and nonionic properties. This product shows excellent detergency and has the characteristic of keeping oil and dirt suspended and not permitting redeposition. In scouring of dyed fabric, this product has a mild stripping action. 

Mixing anionic and cationic surfactants results in the formation of an equimolar catanionic species, which is likely to precipitate even at very low concentration, because it is more hydrophobic (two tails) and less ionic (the charges cancel out at least partially). It was shown, however, that this equimolar catanionic surfactant tends to behave as a hydrophobic amphoteric, i.e. ionic surfactant, which is able to exhibit a linear mixing rule with either of the ionic species provided its proportion remains small, say, less than 20% [57]. For instance, if 5 wt.% of a cationic surfactant is added to 95 wt.% of anionic surfactant, the actual mixture behaves as if it were a mixture of 90 wt.% anionic and 10 wt.% catanionic surfactant. In practice, the pure catanionic species precipitates and hence does not exist as a soluble substance in the microemulsion. Hence, its characteristic parameter has to be estimated by extrapolating the linear trends of the 1 1 mixture, as seen in Fig. 3.10(c). 

Importantly, stability and performance at acidic and alkaline pH extremes are a signature characteristic of these surfactants. Thus, for example, commercial amphoterics such as dihydroxyethyl alkyl glycinate are considered to be excellent thickeners for strongly alkaline oven as well as acid toilet bowl cleaners. Amine oxides enjoy similar properties. Resistance to both acids and bases make them suitable for use in products such as hypochlorite and phosphoric acid hard surface cleaners, hair dyes, corrosion inhibitors, and printing inks [4]. 

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