Applications of cationic surfactants

Fabric softeners represent the single largest outlet for cationic surfactants consuming 200 000 metric tons per year in 1992 [19]. The basic structural requirement for a surfactant useful for fabric softening is the presence of two alkyl groups each with 12-18 carbon atoms and at least one positively charged hydrophile which, in commercial fabric softeners, 

The positively charged nitrogen aids in the deposition of the surfactant onto the fabric and the twin tails provide the lubricity and hand-feel desired by consumers [20]. From this basic structure a medley of materials arise each with its particular exigency being satisfied. 

The hydrophobic portion is typically a fatty alcohol or fatty acid, both of which are materials found in nature and exhibit excellent biodegradability [23-29]. 

Hydrophobe structural features. The twin hydrophobes or tails of a typical softener have four primary elements which can be varied to meet the requirements of the application. The primary elements are the number of carbon atoms, the total degree of saturation, the quantity of polyunsaturates and the cis to trans ratio of the points of unsaturation [24-28, 30, 31]. Additional elements include substitution with noncarbon, hydrogen or oxygen substituents. To date, these have been of little commercial consequence and will not be discussed further. 

The carbon atom number for fabric softener structures usually follows the distribution of common oleochemical feedstocks. The average number is 17.5 for animal-based products such as tallow [32] and this carbon atom number also appears to be optimal for many 

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Developments in this application of cationic surfactants follow the developments in the fabric softener field since traditionally fabric softener surfactants have been employed in hair conditioners. The use of ester-based cationics is drawing attention [68]. Again, the selection of the hydrophobe is seen to control the performance of the cationic surfactant. The conditioning performance of the ester-based cationic is excellent and, additionally, improved static control is demonstrated. This is potentially due to the improved hydration of the hair follicle as a consequence of the more polar nature of the ester-based cationics. 

Doshl and Albright, and earlier Hoffmann, Schrleshelm and this author (13) have recognized that alkylation performance Is related to the presence of oil soluble hydrocarbons, commonly called red oil or conjunct polymers. These species are usually considered to be saturated and unsaturated cations which can function as Intermediates In the transfer of hydride Ions from Isobutane to other alkyl cations. Assuming that hydride transfer Is a limiting factor, the discovery of means to augment the rate should result In Improved alkylation. This report deals with research which has led to the successful application of cationic surfactants for this purpose In commercial plants. 

Selection and Application of Cationic Surfactant in Microflotation and Dynamic Adsorption Layer... 

The application of cationic surfactants was proposed initially by Deqaguin Dukhin (1961) in order to decrease the electrostatic barrier which prevents particle from approaching the bubble surface. This barrier is not important in flotation of normal size particles because they overcome the barrier due to gravity. However, the application of cationic surfactants is recommended in flotation of normal size particles, because it increases the stability of the bubble-particle aggregate by the increase the IT, - % -value. 

Cationic surfactants fall into several categories depending on the nature of their cationic polar heads. Some of them have functional groups susceptible to protonation e.g. amines) and thus display cationic properties particularly in acidic media, while others, such as quaternary ammonium salts, exhibit a permanent positive charge. In household products, cationic surfactants are primarily applied in fabric softeners and hair preparations. Other applications of cationic surfactants include disinfectants and biocides, emulsifiers, wetting agents and processing additives. By volume, the most important cationic surfactants in household products are the alkyl ester ammonium salts that... 

Fredell, D.L., Biological Properties and Applications of Cationic Surfactants, In Surfactant Science Series, Vol. 53, J. Cross and E.J. Singer (eds), Marcel Dekker, New York, 1994, p. 50. 

In this case surfactant micelles or liquid crystal templating were employed, which means that large assemblies of organic molecules were directing the formation of the final structure instead of individual molecules or cations. The initial application of cationic surfactants by Mobil like hexadecyltri-methylammonium bromide or hydroxide has been extended to neutral or even cationic structure-directing agents. Thus, in principle three synthetic procedures exist for preparation of mesoporous molecular sieves ... 

From an analytical chemistry point of view, one important property of micelles is their ability to dissolve different kinds of compounds. Compounds with low solubility in water, or even insoluble, can be dissolved and dispersed by the micelles in aqueous solutions. In analytical chemistry, main applications of cationic surfactants are linked to their solubilization power [1]. In fact, the first applications were mainly focused on the use of micelles to solubilize proteins. The solubilization power of surfactants is obviously observed when working with surfactant concentrations higher than the critical micelle concentration (CMC) value. Micellar media make possible not only to change the solubility of several analytes but also to change their microenvironment and thus to control several physicochemical phenomena. 

Wang and Pek [185] have described a simple titration method applicable to the analysis of cationic surfactants in sea water. Methyl orange and azure A were used as primary dye and secondary dye, respectively. The method is free from interference by high levels of inorganic salts in sea water. 

SPECTROMETRY—IX. LC-MS ANALYSES OF CATIONIC SURFACTANTS METHODS AND APPLICATIONS... 

The vast majority of miniemulsion polymerizations reported in the literature have been stabilized with anionic surfactants, probably because of the widespread application of anionic surfactants in macroemulsion polymerization, and due to their compatibility with neutral or anionic (acid) monomers and anionic initiators. However, Landfester and coworkers [70, 71] have used the cationic surfactants cetyltrimethyl ammonium bromide (CTAB) and cetyltri-methyl ammonium tartrate for the production of styrene miniemulsions. They report that these surfactants produce similar particle sizes to anionic surfactants used at the same levels. Bradley and Grieser [72] report the use of dodecyltrimethyl ammonium chloride for the miniemulsion polymerization of MMA and BA. 

Mesoporous molecular sieves are close to microporous zeolites in their methods of preparation and principal regions of application. These materials are usually synthesized by using supermolecular templates and, in particular, the micelles of cationic surfactants [17]. 

Thus, the mechanism of the supporting influence of cationic surfactants on microflotation and flotation can be different. In microflotation the electrostatic barrier can be decreased, in flotation the contact angle can be increased. Naturally, both effects manifest themselves simultaneously. Li Somasundaran (1990, 1992) observed a bubble recharge due to adsorption of multivalent inorganic cations. Thus, their application is recommended in order to increase the contact angle and to stabilise bubble-particle aggregates. Naturally, selective adsorption of multivalent ions at the water-air interface is important. But even in the absence of adsorption selectivity under equilibrium conditions a deviation from equilibrium can happen due to the increase of adsorption within the r.s.c. This is important for the precalculation of increase of the contact angle caused by cation adsorption. 

The use of cationic surfactants would be of practical interest in applications on negatively charged surfaces. Recently a polyperfluoroether trimethylammonium acetate (PFPE-TMAA), with an average MW of 1124, formed w/c microemulsions up to w = 32 (41). The results compared favorably with those for anionic PFPE-COO NH/ (42). 

Elektorowicz and Hakimipour (2001,2003a) presented a technology that permitted the simultaneous removal of heavy metals and PAHs from natural soil called Simultaneous Electrokinetic Removal of Inorganic and Organic Pollutants (SEKRIOP). This technology used EDTA for metal mobility and zwitterionic surfactants for hydrocarbon mobility. Furthermore, the application of cationic reactive membranes permitted capturing free metallic ions generated by electrokinetic phenomena before their precipitation in the cathode area. The capture of metal-EDTA complexes was done on anionic reactive membranes. 

The approach in this chapter is to review the use of cationic surfactants by application. I have taken this approach rather than a structural approach listing various applications for each type of surfactant. I hope the advantage for the reader will be a more in-depth knowledge of the individual applications and the contribution that the use of cationic surfactants can have. For those applications which are not covered, an understanding of the physical characteristics and behaviours of cationic surfactants from the applications described, should provide the basis for the sound use of these surfactants. 

The use of amine surfactants is varied and found throughout a diverse number of industries. One industry, detergents, employs the largest use of amine surfactants as fabric softener actives. Out of the approximately 700000 metric tons of amine surfactants consumed globally on an annual basis, roughly 50%, or 300000 metric tons, find their way into household, industrial, and textile fabric softener applications. Of the three end-uses as fabric conditioners, the household fabric softener segment commands the lion s share of cationic surfactants at approximately 270000 metric tons. 

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