Presence of mixed surfactant

The presence of mixed surfactant adsorption seems to be a factor in obtaining films with very viscous surfaces [411]. For example, in some cases the addition of a small amount of non-ionic surfactant to a solution of anionic surfactant can enhance foam stability due to the formation of a viscous surface layer, which is possibly a liquid crystalline surface phase in equilibrium with a bulk isotropic solution phase [25,110], In general, some very stable foams can be formed from systems in which a liquid crystal phase is present at lamella surfaces and in equilibrium with an isotropic interior liquid. If only the liquid crystal phase is present, stable foams are not produced. In this connection foam phase diagrams may be used to delineate compositions that will produce stable foams [25,110],... 

A recent study on electrokinetic removal of ethyl benzene from contaminated clay showed a promising use of anionic-nonionic mixed surfactants. Surfactant addition resulted in 1.6-2.4-fold more removal than afforded by EK alone, and a mixed surfactant system, including 0.5% SDS and 2.0% PANNOX 110 (nonyl phenol polyethylene glycol ether) permitted optimal ethyl benzene removal (98%). This indicated that, in the presence of mixed surfactant micelles, the zeta potential of the soil particles significantly increased compared with that seen when anionic surfactant micelles were formed, and electrolytic mobility was thus enhanced (Yuan and Weng, 2004). The use of anionic-nonionic mixed surfactants in EK will also improve the desorption and migration of PAHs. 

As for direct emulsions, the presence of excess surfactant induces depletion interaction followed by phase separation. Such a mechanism was proposed by Binks et al. [ 12] to explain the flocculation of inverse emulsion droplets in the presence of microemulsion-swollen micelles. The microscopic origin of the interaction driven by the presence of the bad solvent is more speculative. From empirical considerations, it can be deduced that surfactant chains mix more easily with alkanes than with vegetable, silicone, and some functionalized oils. The size dependence of such a mechanism, reflected by the shifts in the phase transition thresholds, is... 

Preservatives such as sodium benzoate, sorbic acid, and methyl and propyl parabens have been used in liquid and semisolid dosage forms. There have been reports that the parabens have been inactivated when used in the presence of various surfactants. This loss of activity was thought to be due to the formation of complexes between the preservative and the surfactant. The interaction between polysorbate (Tween) 80 and the parabens has been demonstrated by a dialysis technique (Ravin and Radebaugh, 1990). It has also been shown that molecular complexes form when the parabens are mixed with polyethylene glycol (PEG) and methylcellulose. The degree of binding was less than that observed with Tween 80. Sorbic acid also interacts with Tweens but does not interact with PEGs. The quaternary ammonium compounds are also bound by Tween 80, which reduces their preservative activity. 

The second repulsive energy (referred to as steric repulsion) is produced by the presence of adsorbed surfactant layers of nonionic surfactants, such as alcohol ethoxylates or A-B, A-B-A block, or BA graft copolymers, where B is the anchor chain and A is the stabilizing chain [mostly based on polyethylene oxide (PEO) for aqueous systems]. When two droplets or particles with adsorbed PEO chains of thickness 5 approach a separation distance h such that h < 28, repulsion occurs as a result of two main effects. The first arises as a result of the unfavorable mixing of the PEO chains, when these are in good solvent conditions. This is referred to as Gm x and is given by the following expression ... 

In the presence of anionic surfactants, it is reasonable to expect that the hydrophobic groups of the poljrmer and of the surfactant would combine to form a mixed film at the liquid-air interface. The interactions between the cationic groups of the polymer and the anionic groups of the surfactant would further strengthen the interactions in the monolayer. These effects can be expected to increase the surface and sub-solution viscosity in lamellae and in turn enhance their stability. 

The aminolysis and methanolysis of ionized phenyl salicylate (189) have been examined under micellar conditions. The effect of CTABr on the rates of aminolysis of (189) by -butylamine, piperidine, and pyrrolidine is to bring about a rate decrease (up to 17-fold with pyrrolidine). The results are interpreted in terms of binding constants for the amines with CTABr and the pseudo-phase model.The effects of mixed surfactants SDS and CTABr on the methanolysis of (189) and the alkaline hydrolysis of phenyl benzoate suggest that micellar aggregates are involved in the processes.The effects of NaOH and KBr on the intramolecular general base-catalysed methanolysis of (189) in the presence of CTABr has been investigated. Pseudo-first-order rate constants were not affected by either additive but other changes were noted. The effect of mixed MeCN-water solvents on the same reaction has also been probed. 

The dissociation of protein-surfactant complexes can be induced by the presence of another surfactant with a lower hydrophobic-hydrophilic balance (higher cmc) due to the formation of mixed micelles [105], This effect is illustrated in Fig. 15 for complex formation between insulin and SDS in the presence of a constant concentration of sodium n-decylsulphate (SDeS). In a binary mixture of similar surfactants (SDS + SDeS) that behave as an ideal mixture in the micelles and in the solution, the cmc (C,2 ) is given by [106,107]... 

Ci 3(EO)6 surfactant at 100 °C still presented the y-MnOa phase, but a pure phase of y-MnOOH with high crystallinity could be obtained after hydrothermal treatment at 120 °C in the Ci3(EO)6 solution. It has been known that hydrothermal treatment in water at high temperature of 200 °C could result in the formation of pure y-MnOOH phase (Fig. 1). This indicates that the presence of PEO-surfactant could efficiently reduce the hydrothermal temperature of the pure y-MnOOH formation. SEM images of the y-MnOOH synthesized in the Ci3(EO)6 solution at 120 °C show a lot of rods mixed with small granular particles and a small quantity of nanowires (Fig. 5). 

A second qualitative jump connected with the development of detergent compositions is based on the investigation of mixed surfactant-polymer solutions. It has been shown in [99] that aqueous solutions of water-soluble cellulose esters (a conventional component of detergent compositions) give mixed micelles in mixtures with ionics, and this is a convincing evidence of that the presence of cellulose esters and other polymers in detergent compositions not only prevents re-deposition (secondary deposition of soils on fabrics) but also enhances the detergency of surfactants. 

Chem C-S, Liou Y-C (1998) Effects of mixed surfactants on the styrene miniemulsion polymerization in the presence of an alkyl methacrylate. Macromol Chem Phys 199 2051-2061... 

Emulsion droplets are normally stabilized by enhancing the mechanical strength of the interfacial film formed around the oil droplets (38). by steric stabilizaticm effects, and/or by the presence of charged surfactants which create an electrostatic barrier. The stabilizing factor of the latter is the electrostatic repulsimi of similarly charged droplets. The emulsion stability can be considerably improved with the use of mixed emulsifying agents (39). 

In a similar study, Ebeltoft et al. mixed surfactants (sodium dodecyl sulfate, eetyltrimethylammonium bromide, or cetylpyridinium ehloride) with PSAA and studied the pressiue-area isotherms (70). All the surfaetants appeared to interact with the PSAA and in similar ways. It was concluded that PSAA monolayers are good models for emulsion-stabilizing monolayers in Norwegian crude oils. Monolayers of both PSAA and cmde oil interfacially active fractions responded similarly to the presence of ionic surfactants, indicating analogous dissolution mechanisms. 

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