Abstract
Phase diagrams have been determined as a function of temperature for the following binary and ternary systems containing molecularly distilled or commercial polyoxyethylene (n) oleyl ether (abbreviation; OL-n(m) and OL-n, respectively); OL-6.5(m)-water system and OL-5, OL-7, or OL-8-liquid paraffin-water system. The effect of temperature on the phase equilibria is very remarkable.
The phase diagrams of ternary systems for OL-5 at 50°C, for OL-7 at 70°C, and for OL-8 at 90°C were shown to be very much alike, suggesting that the hydrophile-lipophile balance of nonionics varies with temperature. From the studies of phase diagrams, it seems reasonable to think that the curvature of the oil-water interface changes from convex through flat to concave towards water with the rise of temperature. It was confirmed by the measurement of electrical conductance that the changes in structure of the ternary system with temperature are quite continuous. The molecularly distilled nonionics were found to exhibit the lower phase inversion temperatures and the higher cloud points compared with the commercial ones of the same average ethylene oxide chain length. Also, in the case of the system containing molecularly distilled nonionics, regìon IO where water is solubilized in the oleophilic micelle shifted to the higher temperature with increasing surfactant concentration, while region S where the surfactant crystalline phase separates from the oil phase appeared in the lower temperature region, compared with the system containing commercial nonionics.
Thus, it is clear that the difference in distribution of ethylene oxide chain length, as well as temperature, has a remarkable effect on the phase equilibria in the ternary system.
