Ionic surfactants amphoteric

Amphoteric surfactants can function either as anionic or cationic surfactants, depending on the pH of the system. They contain both anionic and cationic functions in the same moiecuie. More costiy to produce than ionic surfactants, amphoteric surfactants represent oniy about 3% of surfactant voiume in Europe and less than 1% in the United States. They are less irritating than other materials and are largely used in personal care products. A distinction can be made between amphoteric and zwitterionic surfactants. This distinction does not affect their analysis. For the analyst, a more important distinction is between am-photerics with a secondary or tertiary amine group and those containing a quaternary amine function. The former only have cationic properties when protonated at low pH, while the quaternary amines have cationic properties even under alkaline conditions. 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

High polarity is one of the reasons why both the ionic and amphoteric surfactants, and especially their metabolites, are difficult to detect. This property, however, is important for the application tasks of surface-active compounds, but is also the reason for their high water solubility. Due to this fact, their extraction and concentration from the water phase, which can be carried out in a number of very different ways, is not always straightforward. Furthermore, they are often not volatile without decomposition, which thus prevents application of gas chromatographic (GC) separation techniques combined with appropriate detection. This very effective separation method in environmental analysis is thus applicable only for short-chain surfactants and their metabolites following derivatisation of the various polar groups in order to improve their volatility. 

To reduce the potential risk of environmentally harmful surfactants, requirements of a minimum primary degradation amounting to 80% for anionic and non-ionic surfactants was stipulated as far back as 1977 [4]. However, within this early regulation no restraints were included regarding cationic or amphoteric surfactants as these did not hold a significant market share when the laws came into force. 

In a field study performed with nine surfactants from all groups except amphoteric [125], the laboratory effect concentrations were either lower than or similar to the mean in situ EC50 values for cationic and non-ionic surfactants. In contrast, for C12 and C13 LAS, the laboratory EC50 values were higher than the in situ effect concentrations. The short-term photosynthetic response to the same... 

As in aqueous detergent solutions it has become customary to distinguish nonionic and ionic surfactants, thereby subdividing the latter into cationic and anionic surfactants. Some authors also include amphoteric surfactants in this group. Typical representatives of these surfactant types are given in Table 1. The distinction between... 

The HLB concept, introduced in Section 3.6.1 is probably the most useful approach to predicting the type of emulsion that will be stabilized by a given surfactant or surfactant formulation. The HLB concept was introduced [207,209] as an empirical scale that could be used to describe the balance of the size and strength of the hydrophilic and lipophilic groups on an emusifier molecule. Originally used to classify Imperial Chemical Industries non-ionic surfactant series of Spans and Tweens the HLB system has now been applied to many other surfactants, including ionics and amphoterics. 

The hydrophilic portion of a surfactant may carry a negative or positive charge, both positive and negative charges or no charge at all. These are classified respectively as anionic, cationic, amphoteric (or zwitterionic ) or non-ionic surfactant. 

Adsorption can be measured by direct or indirect methods. Direct methods include surface microtome method [46], foam generation method [47] and radio-labelled surfactant adsorption method [48]. These direct methods have several disadvantages. Hence, the amount of surfactant adsorbed per unit area of interface (T) at surface saturation is mostly determined by indirect methods namely surface and interfacial tension measurements along with the application of Gibbs adsorption equations (see Section 2.2.3 and Figure 2.1). Surfactant structure, presence of electrolyte, nature of non-polar liquid and temperature significantly affect the T value. The T values and the area occupied per surfactant molecule at water-air and water-hydrocarbon interfaces for several anionic, cationic, non-ionic and amphoteric surfactants can be found in Chapter 2 of [2]. 

Hidaka H, Nohara K, Zhao J, Pelizzetti E, Serpone N. Photodegradation of surfactants. XIV. Formation of NH and NO, ions for the photocatalyzed mineralization of nitrogen-containing cationic, non-ionic and amphoteric surfactants. J Photochem Photobiol A Chem 1995 91 145-52. 

Petrochemical surfactants are mainly derived from ethylene, propylene, butylenes, benzene, and also naphthalene as building blocks [46]. The most important emulsifiers for emulsion polymerization are anionic and non-ionic surfactants. Cationic and amphoteric surfactants are only used in special cases and are of minor importance as emulsifiers for polymerization. 

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). 

Conventional surfactants are classified as anionic, cationic, non-ionic or amphoteric, according to the charge carried by the surface-active part of the molecule ... 

Betaine-type surfactants do not show anionic character in alkaline solutions or reduced water solubility close to the isoelectric point as other amphoterics do. These surface-active betaines generally exhibit excellent solubility in water and compatibility with anionics over a wide pH range. So, the betaines are often specified as zwitter-ionic surfactants. 

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, ... 

The best agreement with the entire scope of the experimental data was obtained for AGp= -4.25 kJ/mol the theoretical lines calculated from Eq. (3.26) with this AGp value are shown in Fig. 3.61. For the non-ionie and amphoteric surfactants the lines 1 and 2 correspond to AG h =-(2.6 3.0) kJ/mol, and for ionic surfactants the lines 3 and 4 correspond to... 

Chapter 1 gives a systematic view of different classes of surface active substances non-ionic, anionic, cationic, amphoteric and zwitter-ionic surfactants. For each class, the synthesis of a surfactant from different initial substances (including the reaction mechanisms, main production routes, conditions for the best performance etc.), and the chemical analysis of the product properties are summarised. Reference information about manufacturers, nomenclature... 

Leon-Gonzalez et al.[31] proposed an FI spectrophotometric method for the determination of Triton-type non-ionic surfactants based on their reaction with alizarin fluorine blue. An on-line ion-exchange column was incorporated in the system to eliminate interferences from ionic and amphoteric surfactants. In case of interferences from non-ionic surfactants, an on-line Amberlite XAD-4 adsorption column was used to retain selectively the Triton-type surfactant, which was subsequently eluted by ethanol. However, no information was given regarding interferences from refractive index effects at the ethanol/aqueous interface and their elimination. 

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