Insight into the aggregation and phase behavior for aqueous solution of ethylene glycol monobutyl ether with self-assembly induced optical and electrical properties

Ethylene glycol monobutyl ether (EGMBE) is a polar small molecule with amphiphilic characteristics, which can form various aggregates in aqueous solution. The solubility of EGMBE decreases as the temperature increasing with a lower critical solution temperature (LCST). The influence of temperature and salinity on aggregation behavior and solubility of EGMBE were thoroughly investigated in this paper. The phase transition temperatures of EGMBE aqueous solutions with different concentrations were determined and compared with literature. The completed phase diagram of the ternary system (water + NaCl + EGMBE) was constructed. The measured liquidliquid equilibrium (LLE) data can be well fitted to the commonly used empirical equations Othmer-Tobias, Bancroft and Setschenow. The dynamic light scattering (DLS) measurement shows that the particle size of EGMBE aggregates increases with increasing concentration, reaching its maximum at EGMBE mass fraction of about 30 %. Increasing temperature and inorganic salt concentration can both promote the increase of particle size, especially when approaching the phase separation point, the particle size increases sharply, and the corresponding viscosity of EGMBE solution abnormally increases with increasing temperature. The Tyndall effect of EGMBE solution was also observed to be most significant at mass fraction around 30 %. It is interesting to note that the conductivity of EGMBE solution increases with increasing concentration, reaching its maximum value when the EGMBE mass fraction is about 30 %, though EGMBE is not conductive. The investigation of pyrene fluorescence probes and surface/interfacial tension also demonstrated the aggregation and surface adsorption of EGMBE.