Hydrotropes are substances consisting of amphiphilic molecules that are toosmall to self assemble in equilibrium structures in aqueous solutions, but canform dynamic molecular clusters H bonded with water molecules. Somehydrotropes, such as low molecular weight alcohols and amines, can solubilizehydrophobic compounds in aqueous solutions at a mesoscopic scale, around 100nm, with formation of long lived mesoscale droplets. In this work, we report onthe studies of near critical and phase behavior of binary, 2,6-lutidine - H2O,and quasibinary, 2,6-lutidine - H2O - D2O, and tert-butanol - 2-butanol - H2Osolutions in the presence of a solubilized hydrophobic impurity, cyclohexane.In additional to visual observation of fluid phase equilibria, two experimentaltechniques were used - light scattering and small - angle neutron scattering.It was found that the increase of the tert-butanol to 2-butanol ratio affectsthe liquid - liquid equilibria in the quasi-binary system at ambient pressurein the same way as the increase of pressure modifies the phase behavior ofbinary 2-butanol - H2O solutions. The correlation length of criticalfluctuations near the liquid-liquid separation and the size of mesoscaledroplets of solubilized cyclohexane were obtained by dynamic light scatteringand by small - angle neutron scattering. It is shown that the effect of thepresence of small amounts of cyclohexane on the near - critical phase behavioris twofold - the transition temperature changes towards increasing thetwo-phase domain, and long-lived mesoscopic inhomogeneities emerge in themacroscopically homogeneous domain. These homogeneities remain unchanged uponapproach to the critical point of macroscopic phase separation and do not alterthe universal nature of criticality. However, a larger amount of cyclohexanegenerates additional liquid-liquid phase separation at lower temperatures.
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