Nonionic surfactant systems, mixe

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... 

The third factor determining the distribution of surfactant between the solution and the surface phase is represented by the third term from the right in Equation 17. It involves the interaction between the two surfactant species, i.e. Xl2 Analysis of the cmc of mixed surfactant systems (6-7) reveals that there is normally a net attraction when anionic and nonionic surfactants are mixed. This corresponds to a negative Xi2 suggested explanation is that the... 

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. 

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. ... 

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. 

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. 

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. 

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. 

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],... 

Among the purposes of this paper is to report the results of calorimetric measurements of the heats of micellar mixing in some nonideal surfactant systems. Here, attention is focused on interactions of alkyl ethoxylate nonionics with alkyl sulfate and alkyl ethoxylate sulfate surfactants. The use of calorimetry as an alternative technique for the determination of the cmc s of mixed surfactant systems is also demonstrated. Besides providing a direct measurement of the effect of the surfactant structure on the heats of micellar mixing, calorimetric results can also be compared with nonideal mixing theory. This allows the appropriateness of the regular solution approximation used in models of mixed micellization to be assessed. 

Calorimetric measurements can be used to obtain heats of mixing between different surfactant components in nonideal mixed micelles and assess the effects of surfactant structure on the thermodynamics of mixed micellization. Calorimetry can also be successfully applied in measuring the erne s of nonideal mixed surfactant systems. The results of such measurements show that alkyl ethoxylate sulfate surfactants exhibit smaller deviations from ideality and interact significantly less strongly with alkyl ethoxylate nonionics than alkyl sulfates. 

It is worth noting that the effect of temperature on ionic and polyethoxy-lated nonionic surfactants is just opposite. As temperature increases, the nonionics become more lipophilic whereas the ionics turn more hydrophilic. By mixing the two types of surfactants in a proper proportion, these effects could cancel each other out, and the mixture is said to be insensitive to temperature. This interesting feature of ionic-nonionic surfactant mixtures may be considered as a synergy, since it could be very important in practice. Analysis of this feature is not included here, because plenty of information may be found in the literature on applications of such mixtures to equihbrated and emulsified systems [10,71-74]. 

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. 

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