Mixed Nonionic Surfactant Systems

Kunieda H, Yamagata M. Three phase behavior in a mixed nonionic surfactant system. Colloid Polym Sci 1993 271 997-1004. 

Acrylamide was successfully polymerized in a supercritical inverse emulsion composed of an ethane-propane mixture as the continuous phase, water and acrylamide as the dispersed phase, and a mixed nonionic surfactant system as the emulsifier [86], AIBN [2,2 -azobis(isobutyronitrile)] was the initiator. The polymerization was subsequently repeated in supercritical CO2 [87]. The C02-philic surfactant used to produce the inverse emulsion was an amide, end-capped poly(hexafluoropropylene oxide). The process yielded polymers of average molecular weights from 5 x 10 to 7 x 10. ... 

A remarkable contribution in recent years was to have shown for the first time the formation of highly viscoelastic worm-like micelles (Figure 12) in mixed nonionic surfactant systems [110]. This finding allowed to clarify the relation between packing constraints of hydrophobic chains and micellar growth because the complex interactions between counterions (present in ionic surfactant systems) and headgroups had not to be taken into consideration. 

Acharya, D.P., and Kunieda, H. (2003) Formation of viscoelastic wormlike micellar solutions in mixed nonionic surfactant systems. J. Phys. Chem. B, 107, 10168-10175. 

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. 

The same effect is seen when a non—aromatic cationic surfactant/nonionic surfactant system is used. Since the nonideality of mixed micelle formation in this case is due almost entirely to the electrostatic effects and not to any specific interactions between the dissimilar hydrophilic groups, the geometrical effect just discussed will cause the EO groups to be less compactly structured... 

In order to define a ionic/nonionic surfactant solution with high salinity/hardness tolerance, the following criterion should be followed. The mixed micelle should have as large of a negative deviation from ideality as possible. Surfactant mixture characteristics which result in this have already been discussed. The nonionic surfactant should have a high cloud point. Otherwise the amount of nonionic surfactant which can be added to the system is limited to low levels before phase separation occurs. If possible, a mixed ionic surfactant should be used for reasons Just discussed. There is no such benefit to using mixed nonionic surfactants, although this is not necessarily detrimental either. 

The variation of the mixture critical micelle concentration (CMCf ) with temperature and with overall surfactant composition has been studied using ultrafiltration for two binary mixed nonionic/anionic systems. 

The cloud point phenomena as a lower consolute solution temperature is becoming better understood in terms of critical solution theory and the fundamental forces involved for pure nonionic surfactant systems. However, the phenomena may still occur if some ionic surfactant is added to the nonionic surfactant system. A challenge to theoreticians will be to model these mixed ionic/nonionic systems. This will require inclusion of electrostatic considerations in the modeling. 

As already stated, several studies have been pubUshed using nonionic surfactant systems. The formation of viscoelastic micellar solutions in mixed nonionic systems is interesting in basic research-as the relation between packing constraints of hydrophobic chains and micellar growth would be clarified since the complicated interaction between the counterion and headgroup does not occur-as well as in applications such as cosmetics or pharmacy, where the avoidance of ionic additives is often desirable. 

Kunieda, H., Ozawa, K., Aramaki, K., Nakano, A., and Solans, C. (1998) Formation of microemulsions in mixed ionic-nonionic surfactant systems. Langmuir, 14, 260-263. 

Successful attempts have been made to modify/minimize preeipitation in polyelectrolyte/oppositely charged surfactant systems. Laurent and Scott (65) reported such an effect with the addition of simple salts and defined a critical electrolyte concentration (c.e.c.) at which precipitation is totally inhibited. (See Chapter 5 and also Section III.E below.) Likewise, Dubin et al. (66,67) have found inhibitory effects on adding nonionic surfactants to these mixed polymer/surfactant systems, presumably a result of mixed micelle formation. 

Eanun, M. and Salah Al-Diyn, W. 2007 Struetural transitions in the system water/ mixed nonionic surfactants/R (-H)-limonene studied by electrical conductivity and self-diffusion-NMR, J. Disper. Sci. Technol. 28 165-174. 

Fanun, M. 2007. Structure probing of water/mixed nonionic surfactants/caprylic-capric triglyceride system using conductivity and NMR. J. Mol. Liq., 133, 22-27. 

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... 

Investigations of the solubilization of water and aqueous NaCl solutions in mixed reverse micellar systems formed with AOT and nonionic surfactants in hydrocarbons emphasized the presence of a maximum solubilization capacity of water, occurring at a certain concentration of NaCl, which is significantly influenced by the solvent used [132],... 

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