Quaternary ammonium-based cationic surfactants

The most extensively studied of the quaternary ammonium-based cationic surfactants (QACs) is the hydrogenated tallow dimethyl... 

Using this approach Jang and coworkers166 have reported the synthesis of PPy nanoparticles at the 2 nm scale. Typical surfactants used in the preparation of these sub-5-nm particles were quaternary ammonium-based cations such as octyltrimeth-ylammonium bromide or decyltrimethylammonium bromide. Reactions at room temperature produced nanoparticles with diameters on the order of 10 nm, whereas at 70°C ca. 50 nm diameter particles were observed. 

FIGURE 21.3 Structures of some representative cationic surfactants. The vast majority of cationic surfactants are based on the nitrogen atom carrying the cationic charge. Both amine and quaternary ammonium-based products are common (from Ref. 10). 

In nitrogen-based cationic surfactants, it has generally been found that the presence of short-chain alkyl groups (fewer than four carbon atoms) attached to the nitrogen has little apparent effect on the efficiency of adsorption of the molecule. The dominant factor will always be the length of the primary hydrophobic chain. That effect is true whether the alkyl groups are attached to a quaternary ammonium group, an amine oxide, or a heterocyclic nucleus such as pyridine. 

PCH materials offer new opportunities for the rational design of heterogeneous catalyst systems, because the pore size distributions are in the supermicropore to small mesopore range (14-25A) and chemical functionality (e.g., acidity) can be introduced by adjusting the composition of the layered silicate host. The approach to designing PCH materials is based on the use of intercalated quaternary ammonium cations and neutral amines as co-surfactants to direct the interlamellar hydrolysis and condensation polymerization of neutral inorganic precursor (for example, tetraethylorthosilicate, TEOS) within the galleries of an ionic lamellar solid. 

Being internally neutralized, the amphoterics have minimal impact on the biocidal activity of quaternary ammonium salts. For this reason, like the nonionics, they often find use in antimicrobial preparations that are based on cationic surfactants. 

USE Cationic quaternary ammonium surfactant germicide and fungicide. Used in leather processing, textile dyeing. A mildew preventive in silicone-based water repellents. Compatible with many non-ionic detergents. Active in moderately alkaline solns. 

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). 

Although polymeric rheology control additives dominate the market for fracturing fluids, cationic surfactant-based systems have been introduced. Ethoxylated quaternary ammonium salts have been shown to afford viscoelastic aqueous fracturing fluids. The strength and temperature stability of the viscoelastic formulations depends upon the purity of the surfactant. These systems are claimed to break upon exposure to hydrocarbons, thereby affording clean-up behaviour superior to that available when using polymer-based fracture fluids. 

Background. Another form of colloid titration for estimating cationic (quaternary ammonium) compounds is based on a potentiometric procedure and utilizes an eleetrode that is specific to the titrating anionic surfactant chosen. The theory is that the cationic material complexes stoichiometrically with the anionic surfactant. 

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