Surfactant system

Fig. IV 23. Penetration of cholesterol monolayers by CTAB (hexadecyl-trimethylam-monium bromide. [From D. M. Alexander, G. T. Barnes, M. A. McGregor, and K. Walker, Phenomena in Mixed Surfactant Systems, in J. F. Scamehom, ed., ACS Symposium Series 311, p. 133, 1986 (Ref. 269). Copyright 1986, American Chemical Society.]...

An example of the time effects in irreversible adsorption of a surfactant system is shown in Fig. XI-8 for barium dinonylnapthalene sulfonate (an oil additive) adsorbing on Ti02 (anatase). Adsorption was ineversible for aged systems, but much less so for those equilibrating for a short time. The adsorption of aqueous methylene blue (note Section XI-4) on TiOi (anatase) was also irreversible [128]. In these situations it seems necessary to postulate at least a two-stage sequence, such as... 

Mukeqee P and Mysels K J 1970 Critical Micelle Concentrations of Aqueous Surfactant Systems (National Standard Reference Data System, National Bureau of Standards Circular No 36) (Springfield, VA National Teehnieal Information Serviee)... 

The surfactants used in the emulsion polymerization of acryhc monomers are classified as anionic, cationic, or nonionic. Anionic surfactants, such as salts of alkyl sulfates and alkylarene sulfates and phosphates, or nonionic surfactants, such as alkyl or aryl polyoxyethylenes, are most common (87,98—101). Mixed anionic—nonionic surfactant systems are also widely utilized (102—105). 

The inverse emulsion form is made by emulsifying an aqueous monomer solution in a light hydrocarbon oil to form an oil-continuous emulsion stabilized by a surfactant system (21). This is polymerized to form an emulsion of aqueous polymer particle ranging in size from 1.0 to about 10 pm dispersed in oil. By addition of appropriate surfactants, the emulsion is made self-inverting, which means that when it is added to water with agitation, the oil is emulsified and the polymer goes into solution in a few minutes. Alternatively, a surfactant can be added to the water before addition of the inverse polymer emulsion (see Emulsions). 

Surface activity is not limited to aqueous systems, however. AH of the combiaations of aqueous and nonaqueous phases are known to occur, but because water is present as the solvent phase in the overwhelming proportion of commercially important surfactant systems, its presence is assumed in much of the common terminology of industry. Thus, the water-soluble amphipathic groups are often referred to as solubilizing groups. 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

The adsorbed layer at G—L or S—L surfaces ia practical surfactant systems may have a complex composition. The adsorbed molecules or ions may be close-packed forming almost a condensed film with solvent molecules virtually excluded from the surface, or widely spaced and behave somewhat like a two-dimensional gas. The adsorbed film may be multilayer rather than monolayer. Counterions are sometimes present with the surfactant ia the adsorbed layer. Mixed moaolayers are known that iavolve molecular complexes, eg, oae-to-oae complexes of fatty alcohol sulfates with fatty alcohols (10), as well as complexes betweea fatty acids and fatty acid soaps (11). Competitive or preferential adsorption between multiple solutes at G—L and L—L iaterfaces is an important effect ia foaming, foam stabiLizatioa, and defoaming (see Defoamers). 

What are the essential features of surfactant systems An important ingredient is obviously the repulsion between water and nonpolar molecules or molecule parts, the hydrophobic force. This interaction is however highly nontrivial, and its analysis is still an active field of research [4,22,23]. Qualitatively, it is usually attributed to the strong orientational and positional correlations between nonpolar molecules in solution and the surrounding water molecules. The origin of the interaction is therefore entropic free water forms a network of hydrogen bonds. In the neighborhood... 

R. G. Larson. Monte Carlo simulations of microstructural transitions in surfactant systems. J Chem Phys 96 7904-7918, 1992. 

P. Sakya, J. M. Seddon, R. H. Templer, R. J. Mirkin, G. J. T. Tiddy. Micellar cubic phases and their structural relationships the nonionic surfactant system Ci2EOi2/water. Langmuir 75 3706-3714, 1997. 

Mixed Surfactant Systems, edited by Keizo Ogino and Masahiko Abe... 

Modem Characterization Methods of Surfactant Systems, edited by Bernard P. Binks... 

The net result is that detergency performance for mixed active formulations is not so drastically reduced by high water hardness conditions. The improvement in detergency by mixed surfactant systems can be seen not only in under-... 

TABLE 20 Interaction Parameters of Surfactant Systems with Alkanesulfonates at 298.15 K... 

Low-foaming liquid or powdered machine detergents are described using a surfactant system prepared from naturally based raw materials with good biodegradability and detergent properties [135]. These formulations are based on 5-30% alkylpolyglucoside, 5-30% alkyl ether carboxylate, 5-35% soap, and 0-3% of another surfactant. 

Ci2-Ci3 ether carboxylic acid with 4.5-6 mol EO and Ci2-C15 ether carboxylic acid with 9 mol EO as cosurfactant improve the use of alkyl-o-xylene-sulfonate as primary surfactant at different salinity while maintaining good oil solubilization [189]. It is possible to optimize the surfactant system in relation to the crude oil reservoir characteristics. 

AOS is a complex mixture of different chemical species. A typical product composition is as follows [1-7] sodium alkenesulfonate (60-70%) sodium hydroxyalkanesulfonate (30%) sodium disulfonate (0-10%) 6- or 1, 4-sultone (50 ppm) unsulfonated matter (less than 2%) and inorganic salt (mainly sodium sulfate, less than 2.5%). AOS can therefore be regarded as a surfactant system in contrast with other common surfactants such as alkyl sulfates, alkyle-thoxy sulfates, alkanesulfonates, and alkylbenzenesulfonates, which consist of mixtures of their isomers and/or homologs. 

According to [4], IOS consists typically of sodium (3-hydroxysulfonate (85%), sodium alkenesulfonate (10%), sodium y/5-hydroxysulfonates (5%), and residual sultones (usually less than 6 ppmw on active matter). IOS too can be regarded as a surfactant system in the sense referred to above. 

FIG. 2 CMC of linear alkylbenzenesulfonate-a-olefmsulfonate (LABS-AOS) mixed surfactant system. (From Ref. 3.)... 

AOS is a useful surfactant system for the formulation of soap bars. The effect of AOS on the Krafft temperature of soap is shown in Table 27 AOS lowers the Krafft temperature of soap. AOS can also be used to cosolubilize soap in water thereby reducing the waste of insoluble soap as shown in Table 28. 

Alkyl sulfates and alcohol ether sulfates have been established for use in emulsion polymerization. AOS, although it has been used for many detergent applications during the past four decades, does not find any large-scale use as a primary surfactant system in emulsion polymerization. A study by Kreis [92] has shown that AOS surfactants are very well able to produce a small size latex and have excellent foaming characteristics (i.e., foam height and stability) in latex. They should therefore be able to compete with alkyl sulfates and alcohol ether sulfates. 

Lu B, Zheng Y, Scriven LE, Davis HT, Talmon Y, Zakin JL (1998) Effect of variation counterion-to-surfactant ratio on rheology and micro-structures of drag reducing cationic surfactant systems. Rheol Acta 37 528-548... 

Coveney, FM Strange, JH Smith, AL Smith, EG, NMR Studies of Electrophoretic Mobility in Surfactant Systems, Colloids and Surfaces 36, 193, 1989. 

Figure 6.4. Schematic phase diagram for a three-component (oil, water, surfactant) system showing some of the self-assembled structures which form in the various regions.

Attwood D. Florence A.T. (1983) Surfactant Systems, Their Chemistry, Pharmacy and Biology. London Chapman Hall. (2.3.2)... 

This strategy has resulted in entirely new formulations with remarkable benefits. Sustainable Earth (SE) cleaning products combine reagents determined to be safer for human and environmental health with a positively characterized hybrid surfactant system containing a stabilized oxidizing compound. This system eliminates conventional ingredients such as alkyl glycol ethers, alkali builders, alkylphenol ethoxylates, EDTA and ethanolamine. 

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