The critical phenomena of (water+AOT+decane) microemulsion with the molar ratio (ω=30.0) of water to AOT

The critical behavior of {water+AOT+decane} microemulsion with various molar ratios of water to AOT

“…With an assumption of droplet in microemulsion being a pseudo-component and the two coexisting phases having different concentrations of the same droplets, a coexistence curve of temperature against volume fraction / can be drawn in the same way as it was done for the microemulsion with the small size of droplet [15,28].…”

Liquid–Liquid Phase Equilibria and Interactions between Droplets in Water-in-Oil Microemulsions

“…It also has been confirmed by different independent experiments for similar microemulsion systems. [11][12][13][14]33,35 Moreover, in a wider temperature range of |T − T c | < 6 K, we fitted the experimental data of Z cxc to eq 5 with the values of β and Δ being fixed at theoretical values of 0.326 and 0.50, respectively, to obtain the values of B ̂0Z and B ̂1Z , which are listed in columns 4 and 5 of Table 1. From Table 1, it can be seen that the differences between the values of B ̂0Z from the two fits described above and the correction-to-scaling term are not significant, which implies the critical singularity being applicable for the coexistence curves in the temperature range of about 6 K from the critical point.…”

“…It has been found that the droplet–droplet interaction in (water/AOT/ n -alkane) microemulsions was attractive, and its strength increased with w 0 and n of n -alkane. ,,− This interaction was interpreted by an attractive square-well energy potential between two droplets, which seemed to be supported by the fact that the (water/AOT/ n -alkane) microemulsions had LCST and it diminished with the increase in w 0 and n because the depth of the energy potential should increase well with temperature, w 0, and n . ,− However, some studies showed the existence of repulsive enthalpy (or energy) interaction between the droplets, ,,− which was unfavorable to droplet aggregation and phase separation. Therefore, drawing the droplets too close together and inducing the phase separation in AOT-based microemulsions are driven by the positive entropy change due to the release of the solvent molecules confined in the surfactant tails of the droplets; thus, the “energy potential” should have the Gibbs free energy character. , Our recent isothermal titration microcalorimetry (ITC) studies on the (water/AOT/oil) microemulsions confirmed the importance of the entropy effect on the stability of droplets in these microemulsions and found that the droplet interaction enthalpy varied with the nature of the oil phase and the molar ratio of water to surfactants, in some cases, from positive to negative. , However, as a key feature of microemulsion systems, interactions between droplets remain a confusing and challenging issue …”

“…[Water/sodium bis­(2-ethylhexyl)­sulfosuccinate (AOT)/ n -alkane] microemulsions are the most extensively investigated ones among those widely applied microemulsions. − The liquid–liquid phase equilibria of these microemulsions with different droplet concentrations in the two liquid phases commonly show lower critical solution temperatures (LCSTs), and their phase behaviors vary with the molar ratio of water to surfactants ( w 0 ) and the chain type and the chain length ( n ) of the alkane. ,− This was mainly attributed to the variations in the droplet–droplet interactions dependent on many factors; the nature of which has been a matter of long-standing question. ,− …”

“…A microemulsion may be considered as a binary solution of droplets dissolved in a solvent or a ternary solution having renormalized critical exponents. Experimental determinations on the critical exponents corresponding to the width of the coexistence curve, the correlation length, and the osmotic compressibility for microemulsions have been performed by different groups, − ,− where some controversies about whether the criticality of microemulsions belongs to the 3D-Ising universality still existed.…”