Microemulsions mixed surfactants

Fig.1 Formation of reverse micelles in a self-assembled mixed surfactant system. The addition of water tends to link these droplets to form a highly viscous bi-continuous microemulsion with aqueous and isooctane nanochannels separated by the surfactants...

A. Bumajdad and J. Eastoe. Conductivity of mixed surfactant water-in-oil microemulsions. Phys. Chem. Chem. Phys., 6(7) 1597-1602, 2004. 

The gas/liquid and liquid/liquid systems are relevant to biomedical and engineering applications. The large interfacial area in foams, macro- and microemulsions is suitable for rapid mass transfer from gas to liquid or liquid to gas in foams and from one liquid to another or vice versa in macro- and microemulsions. The formation and stability of these systems may be influenced by the chain length compatibility which may also influence the flow through porous media behavior of these systems. Therefore, the present communication deals with the effect of chain length compatibility on the properties of monolayers, foams, macro- and microemulsions. An attempt is made to correlate the chain length compatibility effects with surface properties of mixed surfactants and their flow behavior in porous media in relation to enhanced oil recovery. 

This method is particularly useful for the measurement of very low interfacial tensions (<10 mN m ) that are particularly important in applications such as spontaneous emulsification and the formation of microemulsions. Such low interfacial tensions may also be achieved with emulsions, particularly when mixed surfactant films are used. In this case, a drop of the less-dense liquid A is suspended in a tube containing the second liquid, B. On rotating the whole mass (see Figure 5.4) the drop of the liquid moves to the centre and, with an increasing speed of revolution, the drop elongates as the centrifugal force opposes the interfacial tension force that tends to maintain the spherical shape, which is that having a minimum surface area. 

The synergisms of mixtures of anionic-cationic surfactant systems can be used to form middle-phase micro emulsions without adding short-chain alcohols [109, 110]. The surfactants studied were sodium dihexyl sulphosuccinate and benzethonium chloride. The amount of sodium chloride required for the middle-phase microemulsion decreased dramatically as an equimolar anionic-cationic surfactant mixture was approached. Under optimum middle-phase microemulsion conditions, mixed anionic-cationic surfactant systems solubilised more oil than the anionic surfactant alone. Upadhyaya et al. [109] proposed a model for the interaction of branched-tail surfactants (Fig. 8.16). According to this model the anionic-cationic pair allows oil to penetrate between surfactant tails and increases the oil solubilisation capacity of the surfactant aggregate. Detergency studies were conducted to test the capacity of these mixed surfactant systems to remove oil from... 

Compared with coarse-grained materials, nano-particles can possess unique electronic, magnetic and optical properties. The main principle of producing nano-particles with microemulsions consists in mixing two types of microemulsions, i.e. o/w and w/o microemulsions. In this way, for example, ultra-fine particles are obtained, whose core and external shells consist of Fe salts, and in the intermediate layer copper is contained. To produce microemulsions, anionic surfactants such as Aerosol OT (AOT) are used, one mole of which can solubilise up to 8 moles of the aqueous phase. 

Kunieda intensified the studies on phase behavior and formation of microemulsions in mixed-surfactant systems [66-76], in order to understand the relationship between maximum solubilization of microemulsions and surfactant distribution of mixed surfactants at the water/oil interface in the microemulsion phase. He developed a method to calculate the net composition of each surfactant at the interface in the bicontinuous microemulsions assuming that the monomeric solubihty of each surfactant in oil is the same as in the oil microdomain of the microemulsions [69]. Using this approach, the distribution of surfactants in the different domains of bicontinuous microemulsions (Figure 9) could be quantified [70-75], even if the complete microstracture of these systems was not completely elucidated. 

Zhang and Chan [420] recently reported synthesis of Pt and Pt-Co nanoparticles. The common components in the microemulsions were Triton X-100 as the surfactant, cyclohexane as the oil phase and propan-2-ol as the cosurfactant. The volume percentages in each microemulsion were surfactant 10, oil phase 35, co-surfactant 40 an aqueous phase 15. For pure platinum, the aqueous phase was a solution of H2PtCl6 (microemulsion 1) or hydrazine (microemulsion 2). The two were mixed under stirring to obtain the particles. In case of the composite particles, microemulsion 1 also contained C0CI2 in the aqueous phase. The Pt Co ratio was around 1 2.2. The particles were spherical, 3-4 nm in diameter and had a narrow size distribution. Formation of a small amount of cobalt oxide from unalloyed cobalt cannot be ruled out. 

Unexpected conductance behaviors have been shown by w/o microemulsions obtained from mixed surfactants and mixed cosurfactants [56-621. The transport property depends on the mixing ratio. This is discussed in Section II.B.5. 

Eicke and Meier [122] studied the interfacial charge transport in w/o microemulsions with mixed surfactants (AOT/pentaethylene monododecyi ether) and n-octane and observed unusual reductions in conductance producing a percolation type of pattern in the conductance versus temperature course. The diffuse double layer at the water/oil interface of the droplets was considered to be highly compressed, which accounts for reduced mobility and surface conductivity. 

When surfactant mixtures of practical interest containing multiple species were used (e.g., commercial nonionic surfactants or mixtures of anionic and nonionic surfactants), a maximum in hydrocarbon removal from polyester/cotton fabric similar to that in Figure 4.32 was again seen. For situations where the surfactant oil ratio in the system is large, the typical case for household washing, the maximum occurred at the PIT of a system for which surfactant composition in the films separating oil and water domains of the microemulsion phase was the same as the initial surfactant composition (Raney and Miller, 1987). This result is reasonable since the small amount of hydrocarbon present can dissolve only a small portion of the total surfactant, leaving the remainder, which has neariy the initial composition, to make up the films. It should be noted that here too the PIT is well above the cloud point temperature of the mixed surfactant solution. 

R.K. Mitra, B.K. Pal, and S.P. Moulik 2006 Phase behavior, interfacial composition and thermodynamic properties of mixed surfactant (CTAB and Brij-58) derived w/o microemulsions with 1-butanol and 1-pentanol as cosurfactants and n-heptane and -decane as oils, J. Colloid Interf. Sci. 300, 755-764. 

S. Ajith and A.K. Rakshit 1995 Studies of mixed surfactant microemulsion systems Brij 35 with Tween 20 and sodium dodecyl sulfate, J. Phys. Chem. 99,14778-14783. 

For this reason, the solubilization capacity of the microemulsions formulated with IPM is lower than that observed with R (+)-LlM. The oil behavior can also be governed by the chain compatibility between oil and surfactants. The change in the solubilization capacity behavior of the two oils when the mixing ratio (w/w) of ethoxylated mono-di-glyceride increases to 3/1 or in the quaternary systems water/ethoxylated mono-di-glyceride/oil could be attributed to the better chain compatibility between the mixed surfactants chains and the IPM chain length. 

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