Liquid-liquid equilibria of aqueous two-phase systems formed by Triton X-100 surfactant and thiocyanate salts

Liquid–Liquid Equilibrium of Aqueous Two-Phase Systems Formed by Nonionic Surfactants (Triton X-100, Triton X-165, or Triton X-305), Salts (NaNO3 or KNO3), and Water at Different Temperatures

“…Despite the relative change of the compositions of the phases in equilibrium due to the temperature change, the TL slope (Table 8) for the same global composition was almost unchanged by the temperature increase, according to other studies in the literature. 25,31 This shows that the changes in the positions of the points representing the composition of the upper phase, promoted by temperature increase, occurred maintaining them along the TL. Effect of Cations.…”

“…Specifically, to a surfactant molecule, an increase in temperature promotes (i) the attenuation of hydrogen bonds among water molecules surrounding the hydrophobic segment of the surfactant, which contributes to a decrease in the surfactant’s hydrophobic character, and (ii) the weakening of hydrogen bonds between water molecules and the hydrophilic portion of the surfactant, which contributes to an increase in the surfactant’s hydrophobic character. − However, in concentrated aqueous surfactant solutions (such as in the ATPS studied in this work), the hydrophobic segment of the molecule is majority enclosed within the micelles core, and the impact of temperature increase is particularly on the hydrophilic portion of the surfactant . It is worth noting that the magnitude of this effect is dependent on the other component forming the ATPS, and a temperature increase can lead to a decrease in the biphasic region …”

“…49,50 As the above results show, there is a dependence of the cation effect on the properties of the other component forming the system, in which interactions between the cation and that component can determine salting-in effects of common saltingout agents. 25 This influence extends not only to the formation of ATPSs but also to the intrinsic surfactant/polymer phase separation, including effects on the cloud point or critical micellar concentration. 8 Other examples of anomalies in the salting-out effect observed in ATPSs include: (i) the work of Hey et al, 51 who studied ATPSs formed with PEG 8000 + water + sulfate salts.…”

“…41 The same was observed for the ATPS formed by TX-100, KNO 3 , and water (Figure S1) and has been reported for many ATPSs formed by nonionic surfactants. 25,42 This behavior can be directly attributed to a reduced hydration of the hydrophilic portion of the surfactant at higher temperatures due to the decreased probability of hydrogen bond formation. 43 Specifically, to a surfactant molecule, an increase in temperature promotes (i) the attenuation of hydrogen bonds among water molecules surrounding the hydrophobic segment of the surfactant, which contributes to a decrease in the surfactant's hydrophobic character, and (ii) the weakening of hydrogen bonds between water molecules and the hydrophilic portion of the surfactant, which contributes to an increase in the surfactant's hydrophobic character.…”

“…44−46 However, in concentrated aqueous surfactant solutions (such as in the ATPS studied in this work), the hydrophobic segment of the molecule is majority enclosed within the micelles core, and the impact of temperature increase is particularly on the hydrophilic portion of the surfactant. 13 It is worth noting that the magnitude of this effect is dependent on the other component forming the ATPS, 25 and a temperature increase can lead to a decrease in the biphasic region. 44 Comparing the liquid−liquid equilibrium data for the same global composition of a specific ATPS (Tables 3−6), it is possible to observe that the change of temperature had a large effect on the concentrations of the ATPS components in the upper phase, while the concentration of these components in the lower phase was almost independent of the temperature.…”