Amphoteric Zwitterionic Surfactants

These are surfactants containing both cationic and anionic groups [10]. The most common amphoterics are the N-alkyl betaines, which are derivatives of trimethyl glycine (CH3)3NCH2COOH (thatwas described as betaine). An example of a betaine 

Amphoteric surfactants are sometimes referred to as 2witterionic molecules. They are soluble in water, but their solubility shows a minimum at the i.e.p. Amphoterics show excellent compatibility with other surfactants, forming muKd micelles they are also chemically stable both in acids and alkalis. The surface activity of amphoterics varies widely, and depends on the distance between the charged groups. Amphoterics display a maximum in surface activity at the i.e.p. 

Another class of amphoteric are the N-alkyl amino propionates having the structure R-NHCH2CH2COOH. The NH group is reactive and can react with another acid molecule (e.g., acrylic) to form an amino dipropionate R-N(CH2CH2COOH)2. An alkyl imidazoline-based product can also be produced by reacting alkyl imidozo-line with a chloro acid, but the imidazoHne ring will break down during formation of the amphoteric. 

The change in charge with pH of amphoteric surfactants affects their properties, such as wetting, detergency, and foaming. Atthe i.e.p., the properties of amphoterics resemble those of nonionics very closely, but below and above the i.e.p. the properties shift towards those of cationic and anionic surfactants, respectively. Zwitterionic surfactants have excellent dermatological properties, and also exhibit low eye irritation consequently, they are frequently used in shampoos and other personal care products (e.g., cosmetics). 

The main characteristic of amphoteric surfactants is their dependence on the pH of the solution in which they are dissolved. In acid pH solutions, the molecule acquires a positive charge and it behaves like a cationic, whereas in alkaline pH 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). This can be described by the following scheme  

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Amphiphile-oil-water system, temperature of, 16 424-426 Amphiphiles, 16 420 Amphiphile strength, 6 424 Amphiphilic chemicals, 17 56 Amphiphilic copolymers, 20 482 behavior of, 20 483 well-defined, 20 485-490 Amphiphilic molecules, 15 99-101 Amphiphilic plasticizers, 14 480 Amphiphilic polymer blend, 23 720 Amphiphilic polymers statistical, 20 484-490 stimuli-responsive, 20 482-483 Ampholytes, 9 746-747 Amphoteric cyclocopolymers, water-soluble, 23 721 Amphoteric starches, 4 722 Amphoteric (zwitterionic) surfactants, 24 148... 

Anionic, cationic, amphoteric, zwitterionic surfactants thickening agents benefit agents (silicones, fats and oils, vitamins, plant extracts, sunscreens, alkyl lactate, essential oils, etc.) small amount of soap... 

As mentioned in Chapter 1, there can be thousands of molecules with polar heads and nonpolar tails, usable as surfactants. The applications are also many. Thus, the commercial anionic surfactants, recording about 50% of all surfactant production, are literally used all over the place shampoos, dishwashing detergents and washing powders are some common examples. Cationic surfactants likewise are used in hair-conditioners, fabric softeners, asphalt coating, corrosion inhibitor formulations for metal surfaces etc. The major applications of non-ionic surfactants are in the areas of food and drinks, as also pharmaceuticals and cosmetics. Amphoteric /zwitterionic surfactants have only limited applications one area is cosmetics, especially skin care products. 

Surfactants, 9 22-23, 784. See also Surface-active agents admixture for cement, 5 485 amphoteric, 14 709 amphoteric (zwitterionic), 24 148 anionic, 24 144-146 applications for, 24 119, 155-161... 

Amphoteric (or zwitterionic) surfactants carry a positive and a negative charge so that the net charge is zero. Some lipids, such as phophatidylcholine, are zwitterionic. Since lipids are practically not soluble in water, in a strict sense they do not belong to the class... 

Zwitterionic Surfactant A surfactant molecule whose polar group contains both negatively and positively charged groups. Example lauramidopropylbetaine, CnH23CONH(CH2)3N (CH3)2CH2COO" at neutral and alkaline solution pH. See also Amphoteric surfactant. 

It is important to note that cationic quaternary compounds (monoquats) are rarely used alone in two-in-one shampoos because their substantivity to hair is either greatly reduced in the presence of anionic detergents [102] or else they form undesired precipitates with anionic surfactants. Therefore, combinations of anionic, nonionic, amphoteric, and zwitterionic surfactants are often employed to minimize the formation of insoluble complexes. 

U.S. 6306805 (2001) Bratescu et al. (Stepan) Anionic-cationic bridging surfactant blends bridging surfactants selected from ethoxylated alkanolamide, semipolar nonionic, amphoteric, zwitterionic Clear solutions at a variety of concentrations in water impart cleaning, foaming, and conditioning properties to hair... 

Zwitterionic surfactants, also known as amphoteric surfactants, have both cationic and anionic centers present in the same molecule. Generally, their properties are highly dependent on the pH of the solution. The cationic part is based on primary, secondary, or tertiary amines or quaternary ammonium cations. The anionic part can be more variable and include sulfonates, as in CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-l-propanesulfonate). Other anionic groups are sultaines illustrated by cocamidopropyl hydroxysultaine. Examples of zwitterionic surfactants include betaines (such as cocamidopropyl betaine, dodecyl betaine, lauramidopropyl betaine and cocoamido-2-hydroxypropyl sulfobetaine) and phosphates (such as lecithin). 

Zwitterionic surfactants have positive and negative charges on the head group. Amphoteric surfactants have a head group with a pH-dependent charge. The amine oxide shown in Fig. 3 is zwitterionic at high pH, but becomes cationic as protonation occurs at low pH. Because amphoteric surfactants are generally zwitterionic at some pH. and zwitterionic surfactants are often amphoteric, in practice, the terms zwitterionic and amphoteric are used as synonyms, and the term ampholytic is used to describe both surfactant types. 

The betaines, especially the coconut-oil-derived cocamidopropyl betaines, are the most important zwitterionic surfactants. The name betaine refers to trimethylglycine, which was first isolated from sugar beet beta vulgaris). Cocoamphomonoacetate and cocoamphodiacetate are the most important types for the amphoteric surfactants. The structures and names for both product types are summarized in Table 15.1. 

To this point we have covered the first three of the four general classes of surfactants defined previously. To produce an example of the fourth class, an amphoteric or zwitterionic surfactant, it is only necessary to react dodecyl chloride with a difunctional material such as A,iV-dimethyl-3-aminopropane-1-sulfonic acid... 

Note here that though the terms zwitterionic and amphoteric are often used as a single entity, amphoteric is the more general term, including zwitterionic surfactants. 

Extra mild surfactants (nonionic) polyethoxylated sorbitan ester Combination with amphoteric or zwitterionic surfactants cocamidopropyl betaine Surfactants/glycol soap agents Cationic surfactants Cationic polymers Silicones and derivatives... 

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