Maximum water—surfactant ratio

Figure 5. Maximum water/surfactant ratio of B52/B30 in 80.4/19.6 w/w ethane/propane at 30 C and 500 bar versus acrylamide/ surfactant ratio.

For the 1 M NaCl system the solubility region was further reduced. Fig. 13, and the water solubilization maximum found at even higher surfactant/cosurfactant ratio. The series with the lower ratios of surfactant to cosurfactant showed an uptake of the aqueous solution somewhat similar to the series in the system with 0.5 M NaCl. The series with the surfactant/(cosurfactant + surfactant) ratio equal to 0.4 gave an initial liquid crystal formation lasting for 2-3 days folllowed by a middle phase lasting a longer time. The liquid crystalline and the middle phase layer were both more pronounced for the sample with initial salt concentration equal in the water and in the microemulsion. Fig. 14A, than for the sample with all the salt in the water. Fig. 14B. 

There is in practice at least another composition variable, i.e., the surfactant concentration, but strangely enough it has less effect than the water/oil ratio. This is of course related to the fact that the surfactant concentration is not allowed to change much in most practical cases for cost reasons, from say a minimum of 0.2% to a maximum of 5%. However, since the surfactant concentration does play a role, it will have to be taken into account in another way. 

The size of the water droplet is influenced by the ratio of water to surfactant and the surfactant concentration (at fixed water/oil ratios). As the ratio of water to surfactant increases, the size of the water droplet increases and consequently, the catalyst size also increases. However, a maximum particle size is reached and further increasing the water-to-surfactant ratio has no effect on catalyst size [27, 28, 31]. For example, in a microemulsion system of water/n-heptane with the surfactant sodium dioctyl sulfosuccinate the Pt-Ru particle size increases from 2.4 0.1 to 3.2 0.1 nm when the ratio of water to sodium dioctyl sulfosuccinate increases from 4 to 8 [28]. However, increasing the water-to-dioctyl-sulfosuccinate ratio to 10 does not result in any fijrther increase in catalyst size [28]. Droplet size can also be controlled by varying the surfactant concentration while keeping the concentrations of water and oil constant. For example, increasing the surfactant concentration, with constant water and oil concentrations, increases the number of droplets. As a result, droplet size decreases, resulting in fewer metal ions per droplet and a consequently decreased particle size. 

Figure 15.6. Self-diffusion measurements of the oil component in a microemulsion containing didodecyldimethylammonium sulfate (DDAS)/dodecane/water (D2O) at different ratios of surfactant to oil. The X-axis represents the total volume of oil plus surfactant, i.e. the volume fraction of aggregates/micelles according to equation (15.7) represents oil diffusion when the system solubilizes a maximum amount of oil (the emulsification failure line), with the continuous line being a fit of equation (15.7) to the data represents the oil diffusion at lower oil-to-surfactant ratios when the system forms prolate structures the corresponding line is simply a guide for the eye (Nyden, unpublished data)...

The amount of water solubilized in a reverse micelle solution is commonly referred to as W, the molar ratio of water to surfactant, and this is also a good qualitative indicator of micelle size. This is an extremely important parameter since it will determine the number of surfactant molecules per micelle and is the main factor affecting micelle size. For an (AOT)/iso-octane/H20 system, the maximum Wq is around 60 [16], and above this value the transparent reverse micelle solution becomes a turbid emulsion, and phase separation may occur. The effect of salt type and concentration on water solubilization is important. Cations with a smaller hydration size, but the same ionic charge, result in less solubilization than cations with a large hydration size [17,18]. Micelle size depends on the salt type and concentration, solvent, surfactant type and concentration, and also temperature. 

Fig. 2.2.2 Effect of the water-io-surfactant molar ratio (/ ) on the wavelength of maximum Ru(Bpy), fluorescence intensity in the NP-5/cyclohexane/waier and NP-5/cyclohexane/ water/ammonia microemulsion systems CJ1 = 460 nm. (From Ref. 25.)...

On the basis of these inequalities, one can conclude that C passes through an extremum. The extremum is a maximum because (i) C is small for small values of h, due to the low adsorbability caused by the strong interactions between surfactant and oil (ii) it increases with h, due to the increasing favorable interactions between the head group of the surfactant and water (iii) passes through a maximum when the decrease of CG with increasing h compensates for the ratio of increases of r with h and CG it becomes again small for h =h0. 

The results showed distinct and regular changes for the aqueous solubility region in pentanol surfactant mixtures. With increased electrolyte content, the "minimum amount of water for solubility was enhanced, the solubility limit towards the pentanol water axis was shifted to higher soap concentrations, and the "maximum solubility of the aqueous sodium chloride solution was obtained for higher surfactant alcohol ratios (Figure 2). 

Dispersions have proved to be much more stable to gas injection than to water injection(2,4). The maximum ratio of water to surfactant solution that can be used in a three-phase cycle of surfactant solution, gas, and water is uncertain, but is probably no more than three(4). 

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