Cationic surfactants basic properties

Even if this class covers the smallest market segment, amphoteric surfactants still remain useful because of their unique properties, which justifies their comparably high manufacturing costs. Since they have partial anionic and cationic character, they can be compatible, under specific conditions, with both anionic and cationic surfactants. They can function in acid or basic pH systems and, at their isoelectric point, they exhibit special behaviour. Many amphoteric surfactants demonstrate exceptional foaming and detergency properties combined with antistatic effects. 

The ecological behaviour of cationic surfactants is basically determined by their basic physico-chemical property, i.e. the strong adsorption on surfaces, e.g. on clay minerals or activated sludge, thus leading to their elimination in water treatment plants and water courses. Although physico-chemical processes are primarily effective in the elimination of cationic surfactants of the quaternary-ammonium-ion type in waste-water treatment, there are indications on the basis of experiments that these substances are aerobically biodegradable. 

Polar solvents may interact strongly with a mineral oxide surface. In principle, the adsorption of die solvent must be considered. Claesson [13] studied the adsorption of fatty acids by sihca from solvents of various polarities. The results show that polar solvents compete with the solute for available sites on the surface, while nonpolar solvents show little competition. The polarity of the solvent is often determined from the measured dielectric properties. Krishnakumar and Somasundaran [13] studied surfactant adsorption on to silica and alumina from solvents with various dielectric properties. The aim of the study was to look at the effect of adsorbent and smfactant acidities and solvent polarity on the adsorption properties of the surfactant molecules. They used anionic and cationic surfactants as adsorption probes. The results show that polar interactions control the adsorption from solvents of low dielectric properties while hydrocarbon chain interactions with the surface play an important role in determining adsorption from solvents of higher dielectric properties. It was also found that an acidic surfactant interacts strongly with a basic adsorbent, and vice versa. One should be aware that the polarity of a molecule as measmed from the dielechic properties is not always eorrelated with the ability of the molecules to form ion pairs. For example, dimethylformamide and nihomethane have almost equal dielechic constants. However, the extent of ion pairing in nihomethane is much greater than that in dimethylformamide. Thus, the solvent acidity and basicity are the physical properties which can best characterize the ability of the solvent to compete with the solute for available sites on the mineral surface. 

Sodium dodecylbenzenesulfonate is undoubtedly the anionic surfactant used in the greatest amount because it is the basic component in almost all laundry and dishwashing detergents in powder and liquid forms. However, alcohol and alcohol ether sulfates are the more versatile anionic surfactants because their properties vary, with the alkyl chain, with the number of moles of ethylene oxide added to the base alcohol and with the cation. Consequently, alcohol and alcohol ether sulfates are used in almost all scientific, consumer, and industrial applications. 

The basic physico-chemical properties of the fatty amine surfactants drive their utilities as adjuvants. Such molecules consist of a water-insoluble hydrophobic unit, in this case derived from tallow fatty acid. The water-soluble unit of the molecules consist of two chains of polymeric alkoxides, in these cases ethylene oxide and/or another alkylene oxide, such as propylene oxide. A nitrogen atom in the middle of the molecule connects the water-soluble and water-insoluble parts. Due to the electronic properties of nitrogen with respect to the carbon atom connectors which are usual in surfactants, the molecule has an overall cationic character, thus resulting in improved substantivity (adherence) to the leaf surface. 

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