System water-decane

Figure 4.3 Phase diagrams of the system water-decane-CioE4 at equal volumes of water and decane without additive and with the hydrophilic alkyl polyethylene oxides C8E91 and C 2E93, respectively, at 8 = 0.10.

Figure 4.9 Phase diagram of the system water-decane-CioE4 at equal volume fractions of water and decane as a function of the temperature T and the surfactant concentration cf>7. At low (f>7 there is a three-phase coexistence, while at moderate cf>7 the one-phase bicontinuous microemulsion appears. At even higher cf>7 the lamellar phase appears. At high and low temperatures a microemulsion phase coexists with either excess water or oil. The polymer fraction cf>p is raised symmetrically for the water- and oil-soluble polymers, and the one-phase microemulsion window closes continuously. The 2 K temperature shift is due to the use of heavy water. (From Ref. [40], reprinted with permission of the American Chemical Society.)...

A somewhat different water, decane, and AOT microemulsion system has been studied by Feldman and coworkers [25] where temperature was used as the field variable in driving microstructural transitions. This system had a composition (volume percent) of 21.30% water, 61.15% decane, and 17.55% AOT. Counterions (sodium ions) were assigned as the dominant charge transport carriers below and above the percolation threshold in electrical... 

Figure 6. The repeat distance d (a), the thickness of the oil layer 62 (bX and the product dip (c) vs

The dielectric relaxation properties in a sodium bis(2-ethylhexyl) sulfosuc-cinate (AOT)-water-decane microemulsion near the percolation temperature threshold have been investigated in a broad temperature region [47,143,147]. The dielectric measurements of ionic microemulsions were carried out using the TDS in a time window with a total time interval of 1 ps. It was found that the system exhibits a complex nonexponential relaxation behavior that is strongly temperature-dependent (Figure 8). 

Borkovec et al. [59] also reported on a two-stage percolation process for the ME AOT (Aerosol OT, bis(2-ethylhexyl)sodium sulfosuccinate) system AOT-decane-water. The structural inversions were investigated using viscosity, conductivity, and electro-optical effect measurements. The viscosity results showed a characteristic profile with two maxima, which was interpreted as evidence for two symmetrical percolation processes an oil percolation on the water-rich side of the phase diagram and a water percolation process on the oil-rich side. 

Figure 4. Phase diagrams of the ternary systems. Water, AOT, isooctane or decane. The phase diagram with decane has been established by Assih et al.

In these studies, the system water/Brij 30 (polyoxyethylene lauryl ether with an average of 4mol ethylene oxide/decane) was chosen as a model to obtain O/W emulsions. The results showed that nanoemulsions with droplet sizes on the order of 50 nm were formed only when water was added to mixtures of surfactant and oil (method B), whereby an inversion from a W/O emulsion to an O/W nanoemulsion occurred. 

The droplet size is considered in several references [55-58]. The works of Suarez considered water-decane-AOT-l-propanol(l-butanol)-PEO and water-cyclohexane-SDS-l-pentanol-PEO systems and found that the droplet size decreases as a function of the polymer content. The latter works of the Brown group considered water-cyclohexane-... 

Unlike the experiments carried out below the cloud point temperature, appreciable solubilisation of oil was observed in the time frame of the study, as indicated by upward movement of the oil-microemulsion interface. Similar phenomena were observed with both tetradecane and hexadecane as the oil phases. When the temperature of the system was raised to just below the PITs of the hydrocarbons with C12E5 (45°C for tetradecane and 50°C for hexadecane), two intermediate phases formed when the initial dispersion of Li drops in the water contacted the oil. One was the lamellar liquid crystalline phase La (probably containing some dispersed water). Above it was a middle-phase microemulsion. In contrast to the studies below the cloud point temperature, there was appreciable solubilisation of hydrocarbon into the two intermediate phases. A similar progression of phases was found at 35°C using n-decane as the hydrocarbon. At this temperature, which is near the PIT of the water/decane/C Es system, the existence of a two-phase dispersion of La and water below the middle-phase microemulsion was clearly evident. These results can be utilised to optimise surfactant systems in cleaners, and in particular to improve the removal of oily soils. The formation of microemulsions is also described in the context of the pre-treatment of oil-stained textiles with a mixture of water, surfactants and co-surfactants. 

Using one of the pure alkyl aryl sulfonates with water, sodium chloride and decane, we are investigating simultaneously the phase behavior, the structure of the phases, and the interfacial tensions between them. Ultralow tensions are observed in this system (10), and it is important to know why they occur, when they do (13). Our first aim is to establish the equilibrium phase diagram of surfactant-water-decane as a function of... 

Figure 23 Temperature dependence of the deuterium relaxation rate difference. A/ , measured with deuterium-labeled C12E5, in the ternary C12E5-water-decane system. The two volume fractions, (1) = 0.23 and 0.12, respectively, refer to the total volume fraction of surfactant and oil for a constant surfactant/oil ratio 0 /0 = 0.815. At lower temperatures the system forms spherical oil droplets in water and AR is the same for the two volume fractions. Above a certain temperature, the droplets grow in size as demonstrated by the increase in AR. (Data from Ref. 58.)...

In the AOT-water-oil system, when the temperature is increased sufficiently a cloud point (critical point) is reached. At temperatures well below this transition temperature the viscosity data are in agreement with a simple hard-sphere model. Upon approaching the critical point one first notices a relatively moderate increase of viscosity by about a factor of 4 followed by a critical divergence of viscosity very close to the cloud point. The critical divergence of such a system (with decane as oil) at the critical temperature was studied and was shown to scale almost Ising-like according to rj [ Tc - T)/Tc] with a critical exponent of 0.03 [69]. 

Typically such W/O microemulsions (like their O/W counterparts) are Newtonian fluids up to shear rates of at least 10 s .This has, for instance, been verified for the system ammonium heptadecylbenzene-/ -sulfonate-cyclohexanol-water-decane [72]. This is a result of quite general validity i.e., such systems are normally of low viscosity and behave as Newtonian fluids up to high shear rates or shear frequencies. 

The dielectric measurements performed for the AOT/water/decane and AOT/water/hexane micro emulsions at the volume fraction of the dispersed phase of (p= 0.13 demonstrate the significant shift of the percolation region to the direction of high temperatures when the oil chain lengfli decreased (Fig. 18) (118, 119). However, the values of s for bofli die microemulsions are die same at low temperatures, i.e., below die percolation onset. Thus, diose results do not support die hypothesis that the clustering can be responsible for the temperature behavior of die static dielectric permittivity at F < and it must be the internal processes within a droplet diat determine the behavior of the dielectric polarization in the system. 

Figure 3.3 NMR relaxation data (1 /T2-I/T,) for the systems with decane or hexadecane with C,2E5 and water as a function of droplet volume fraction. The figure is adapted from ref [113] and data taken for hexane from ref [113] and for decane from ref [34].

Figure 3.11 NMR relaxation as function of temperature for the (a) Ci2Es-water-decane system and for (b) the Ci2Es-water-hexadecane system at five droplet...

Figure 3.12 Self-diffusion coefficient plotted versus temperature for two (in a) respective three (in b) concentrations, (a) the Ci2Es-water-decane, system and (b) the Ci2Es-water-hexadecane system. The dotted lines are the oil diffusion and the permanent...

Figure 3.13 SANS data and their fits versus scattering vector q, at chosen scattering length densities for (a) the Ci2E5-water-decane system, and for (b) the CijEj-water-...

Figure 3.14 Intensity in the forward direction versus scattering length density of the water phase for (a) the C 2E5-water-decane system.

Figure 3.IS Results from dynamic lightscattering measurements on (a) the Ci2Es-water-decane system, and (b) the Ci2E5-water-hexadecane system. Results from the static light-scattering measurements on...

Figure 3.20 The phase diagrams for the Lund cut with 0.85 1 surfactant-to-oil volume ratio for the Ci2Es-water-decane system, where part of the oil is substituted with lidocaine. Without lidocaine (circles), with...

C Es-water-decane system, where part of the lidocaine. The figures adapted from and data... 

Figure 3.24 The difference with temperature for the system CnEj-water-decane, where 1% of the oil is substituted with lidocaine at 298 K (circles), 300 K (squares) and 302 K (diamonds). The figure adapted from and data taken from ref [114].

Rabie et al [ 122] reported similar results with heptanol, a relatively long-chain alcohol in the system AOT/decane/water and showed that by using the titration method (see Section 3.3), the value of w (around 45 in absence of heptanol) increased to about 90 with a heptanol/AOT molar ratio of about 0.35. As expected, the w value decreased drastically with further addition of heptanol. It was concluded that when in excess, the alcohol acts as a co-solvent rather than a co-surfactant. The observation of Caillet et al. [ 126] that the water solubilization capacity of different alcohols ([ 1 -alkanol]/[AOT] = 0.5, temperature 25"C) reaches a peak in the system AOT/n-decane/ water with increase of the chain length up to C7 has been already mentioned. As for benzene, not a usual co-surfactant, Rabie et al. [122] confirmed a rise of w from about 45 to a peak of 75 at a benzene/AOT molar ratio close to 10. 

---