Cationic surfactants common types

Many different types of foaming agents are used, but nonionic surfactants are the most common, eg, ethoxylated fatty alcohols, fatty acid alkanolamides, fatty amine oxides, nonylphenol ethoxylates, and octylphenol ethoxylates, to name a few (see Alkylphenols). Anionic surfactants can be used, but with caution, due to potential complexing with cationic polymers commonly used in mousses. 

The common gangue material quartz (silica) is naturally hydrophilic and can be easily separated in this way from hydrophobic materials such as talc, molybdenite, metal sulphides and some types of coal. Minerals which are hydrophilic can usually be made hydrophobic by adding surfactant (referred to as an activator ) to the solution which selectively adsorbs on the required grains. For example, cationic surfactants (e.g. CTAB) will adsorb onto most negatively charged surfaces whereas anionic surfactants (e.g. SDS) will not. Optimum flotation conditions are usually obtained by experiment using a model test cell called a Hallimond tube . In addition to activator compounds, frothers which are also surfactants are added to stabilize the foam produced at the top of the flotation chamber. Mixtures of non-ionic and ionic surfactant molecules make the best frothers. As examples of the remarkable efficiency of the process, only 45 g of collector and 35 g of frother are required to float 1 ton of quartz and only 30 g of collector will separate 3 tons of sulphide ore. 

Emulsions are a class of disperse systems consisting of two immiscible liquids, one constituting the droplets (the disperse phase) and the second the dispersion medium. The most common class of emulsions is those whereby the droplets constitute the oil phase and the medium is an aqueous solution (referred to as O/W emulsions) or where the droplets constitute the disperse phase, with the oil being the continuous phase (W/O emulsions). To disperse a liquid into another immiscible liquid requires a third component, referred to as the emulsifier, which in most cases is a surfactant. Several types of emulsifiers may be used to prepare the system, ranging from anionic, cationic, zwitterionic, and nonioinic surfactants to more specialized emulsifiers of the polymeric type, referred to as polymeric... 

A great variety of surfactants have been used in microemulsion formation. These include common soaps, other anionic and cationic surfactants, nonionic surfactants of the polyethylene oxide type, and other structures. The hydrophobic part contains one or two linear or branched hydrocarbon chains containing about 8-18 carbon atoms. Quite often microemulsions require, in addition to oil, water, and surfactant, the presence of simple electrolytes, alcohols, and/or other weakly surface-active substances. 

Anionic surfactants (such as sodium dodecyl sulfate), cationic surfactants (such as cetyltrimethylammonium bromide) (163), and nonionic surfactants (such as the polyoxyethylenated alkylphenols) (136,338) have been used in preparing emulsions. Different types of surfactants can be used in the same recipe (377) to provide additional stability under specific conditions. For example, mixtures of anionic and nonionic surfactants are common. The anionic surfactant controls the particle nucleation stage, and the nonionic surfactant imparts additional electrolyte tolerance, mechanical shear stability (345), and freeze-thaw stability. Mixtures of anionic and cationic surfactants tend to coagulate and are to be avoided. 

Nanoclays can be categorized into cationic and anionic types. Cationic nanoclays are based on smectite clays. An example is montmorillonite (MMT), a hydrated Al, Mg silicate that may contain cations such as Na+ and Ca++ between the anionic layers. In contrast, anionic clays contain cationic layers and anions such as Cr and in the interlayer space. Typical examples include layered double hydroxides (LDH) and hydrotalcite (HT), a mostly synthetic hydrated magnesium and aluminum carbonate salt. Whereas MMT is commonly used as a nanofiller to improve thermal, mechanical, and barrier properties, LDHs have many attractive properties that lead to application as surfactant adsorbents, biohybrid materials, antacid food formulations, acid neutralizers, and active pharmaceutical ingredients excipients [37, 13, 28, 14, 35]. 

Conventional ionization techniques such as El or Cl are less well suited for the characterization of quaternary amines, which are the most common cationic surfactants. Due to their thermal instability and low volatility, their corresponding mass spectra only show decomposition products and fragment ions that make it impossible to analyze environmental samples of unknown composition. By the use of FAB-MS and FD-MS, however, ionization of quaternary amines can be achieved without decomposition. FAB spectra are characterized by strong quasimolecular ions as well as structure-specific ions [95,102]. FAB in combination with collisionally activated decomposition (CAD) in a tandem mass spectrometer enables a clear differentiation between quasimolecular and fragment ions, which is often difficult using FAB alone [102]. FD spectra of quaternary amines are dominated by quasimolecular ions as already described for other surfactant types [102]. By combining PD and CAD in a tandem MS, it is even possible to obtain fragment ions for the structure elucidation of individual cationic surfactants in environmental samples [103]. 

The choice of surfactant is critical to the size, shape and stability of the particles. It should be chemically inert with respect to all other components of the microemulsion. This is particularly important when the system contains oxidizing or reducing agents. Surfactants are classified as cationic, anionic, non-ionic or zwitteri-onic, depending on the type of charge on their head group. Two of the most commonly used surfactants are the anionic surfactant sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and the cationic surfactant CTAB. 

It should be pointed out that although the preceding discussion was concerned with the use of alcohols as cosurfactants in microemulsion formation, many other types of material can also be used to the same end. Especially important are primary amines (commonly used with cationic surfactants) and thiols. 

Numerous laboratory sorption studies have been conducted for the most common surfactants non-ionics, such as AE and alkylphenol ethox-ylates (APEOs) anionics such as LAS, secondary alkane sulfonates (SASs) and sodium dodecylsulfates (SDS) and on different natural sorbents [3,8,15-17], Until now, cationic and amphoteric surfactants have received less study than the other types, probably because they represent only 5 and 2%, respectively, of the total surfactant consumption in Western Europe (1998) [18]. 

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