Surfactants anionic-nonionic systems

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). 

Surfactants employed for w/o-ME formation, listed in Table 1, are more lipophilic than those employed in aqueous systems, e.g., for micelles or oil-in-water emulsions, having a hydrophilic-lipophilic balance (HLB) value of around 8-11 [4-40]. The most commonly employed surfactant for w/o-ME formation is Aerosol-OT, or AOT [sodium bis(2-ethylhexyl) sulfosuccinate], containing an anionic sulfonate headgroup and two hydrocarbon tails. Common cationic surfactants, such as cetyl trimethyl ammonium bromide (CTAB) and trioctylmethyl ammonium bromide (TOMAC), have also fulfilled this purpose however, cosurfactants (e.g., fatty alcohols, such as 1-butanol or 1-octanol) must be added for a monophasic w/o-ME (Winsor IV) system to occur. Nonionic and mixed ionic-nonionic surfactant systems have received a great deal of attention recently because they are more biocompatible and they promote less inactivation of biomolecules compared to ionic surfactants. Surfactants with two or more hydrophobic tail groups of different lengths frequently form w/o-MEs more readily than one-tailed surfactants without the requirement of cosurfactant, perhaps because of their wedge-shaped molecular structure [17,41]. 

Emulsion Polymerizations, eg. vinyl acetate [VAc]/ABDA, VAc/ethylene [VAE]/ABDA, butyl acrylate [BA]/ABDA, were done under nitrogen using mixed anionic/nonlonic or nonionic surfactant systems with a redox Initiator, eg. t-butyl hydroperoxide plus sodium formaldehyde sulfoxylate. Base monomer addition was batch or batch plus delay comonomer additions were delay. 

Rabagliati et al. (14) studied the polymerization of styrene in a three phase system containing an anionic-nonionic surfactant mixture and brine. Both AIBN and potassium persulfate initiators were used. The system was reported to be microemulsion continuous and even multicontinuous. (14). No autoacceleration was observed and the authors concluded that the polymerization exhibits an inverse dependence of the degree of polymerization on initiator concentration, similar to bulk solution polymerization. 

In the nonionic system observed under EVM, the initial microemulsion showed no tendency of gelation until it reached 60 C. After reaching 60<>C, the system gels and starts to polymerize after 10-12 hours. As polymerization proceeds, the water separates out. After about 20-24 hours, the gel starts to become a solid with an excess emulsion phase formed at the bottom. The polymerization is essentially complete after 36 hours. Due to different modes of polymerization in the anionic and nonionic surfactant systems, the mechanical properties of the solid are different. The polymers obtsuned from anionic microemulsions are brittle, while those obtmned from nonionic microemulsions are ductile. 

Several objectives motivated the extension of ACN studies to light compressible solvents [12]. Initial studies of AOT in such solvents had demonstrated the possibility of intriguing solvent effects [20,21,32], which could be clarified by additional experiments. A second objective was to test the concepts generated from the thermodynamic models that were developed for the AOT-brine-propane system [25,44]. A final objective was to study the behavior of nonionic surfactant systems as a complement to AOT systems. Nonionic systems provide an enhanced opportunity to study temperature effects on surfactant phase behavior, as nonionic surfactants are much more responsive to temperature than the anionic surfactant AOT. 

RE Anton, H Rivas, JL Salager. Surfactant-oil-water systems near the affinity inversion - Part X Emulsions made with anionic-nonionic surfactant mixtures. J Dispers Sci Technol 17 553—566, 1996. 

Ethoxylated quaternary salts are used primarily as lightconditioning additives in both anionic and nonionic surfactant systems. However, these quaternaries have less substantivity due to their greater water solubility. Increasing either the alkyl chain length or the number of alkyl groups results in increased conditioning performance (see Figure 14.28). 

We note that for nonionic surfactants, the addition of salt is about 100 times less efficient compared with ionic surfactants. In the latter case, there is a remarkable effect even if the salt concentration is on the order of 10 mM, while for nonionic surfactants there is an effect for salt concentrations even on the order of 1 M. In the latter case, the mechanism is that salt dehydrates the EO chain, while in the former case the mechanism is that the salt increases the counterion binding and hence decreases the ionic repulsion between the surfactant head groups. Thus, by knowing the mechanisms, we conclude that, for the ionic systems, adding a divalent counterion would be much more efficient compared with a monovalent counterion. For the nonionic surfactant systems, the anion is the deciding partner, while changing the cation hardly affects the CPP of the system. Here di- and trivalent anions are much more efficient compared with monovalent anions. 

Schick and Schmolka (15) have summarized the influence of electrolytes on the foam film thickness and stability for nonionic surfactant systems. Specific effects of such anions on the film blackening times have been reported. The order of the magnitude of the effect follows the lyotropic series, where SCN and Cl act as... 

Mixed anionic and nonionic surfactant systems have been widely used in industry to manufacture latex products. Anionic surfactants can provide electrostatic repulsion force between two similarly charged electric double layers. By contrast, nonionic surfactants can impart two approaching latex particles... 

Uses Liq. foam control agent for anionic or nonionic surfactant systems suggested for applies, where soaps or detergents are the major cause of foam problems. CNCDefoamerXD2-123D [CNC Infl.j Uses Cone. liq. defoamer for acid phosphate ore processing. CNCDefoamerXD3-1C [CNC Int l.]... 

Islam, M.N., Okano, T., Kato, T. Surface phase behavior of a mixed system of anionic — nonionic surfactants studied by Brewster angle microscopy and polarization modulation infrared reflection — adsorption spectroscopy. Langmuir 2002, 78(26), 10068-10074. 

Eigure 6 illustrates how the three tensions among the top, middle, and bottom phases depend on temperature for a system of nonionic surfactant—oil—water (38), or on salinity for a representative system of anionic surfactant—cosurfactant—oil—water and electrolyte (39). As T approaches from lower temperatures, the composition of M approaches the composition of T, and the iaterfacial teasioa betweea them, goes to 2ero at T =. ... 

The surfactant most commonly used is the anionic detergent sodium lauryl sulfate. Other surfactants that have been used include sodium dodecylbenzene sulfonate [25155-30-0] sodium A/-lauroyl sarcosinate or Gardol [137-16-6] and sodium cocomonoglyceride sulfonate [3694-90-4]. Cationic and nonionic surfactants are not used for several reasons, including incompatibiUty with the abrasive system and lack of high foaming capabiUty. 

The composition of a typical IOS system prepared by Stapersma et al. [4] is shown in Table 2, along with the analytical data of an AOS with the same chain length. Compositions containing IOS, a nonionic surfactant, glycols, and another salt-tolerant anionic surfactant which are pourable and pumpable at 20°C and can be used in the manufacturing of detergent compositions, have also been described by Stapersma et al. [36]. 

To reduce the strong interactions occurring between protein and surfactant with AOT systems during LLE, anionic [8,32] and nonionic surfactants [30,33,142] and other interfacial additives [88,124,143] have been included. An improvement on the percent extraction of protein has also been reported for several of these cases [29,32,33,124,142,143]. 

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