WETTING TRANSITIONS AT LIQUID-LIQUID INTERFACES IN 3-COMPONENT WATER PLUS OIL PLUS NONIONIC SURFACTANT SYSTEMS

There is a controversial problem concerning the wetting properties in the three-liquid-phase region of the system water + n-hexadecane + C(6 )E(2), where C(i)E(j) denotes the nonionic surfactant poly(oxyethylene ) alcohol CjH2i+l(OCH2CH2)OH, In this study, both interfacial tension measurements and direct contact angle measurements are used to further reconfirm that the middle phase of this system does exhibit a wetting transition at the interface separating the upper and the lower phase as temperature is increased towards the upper critical consolute tempe rature. The effect of chain length of oil on the wetting transition is also discussed in the ternary system water + n-alkane + C(6)E(2) by U sing three different oils: n-tetradecane, n-hexadecane, and n-octadeca ne. The wetting transition temperature increases as the chain length o f the n-alkane increases; As temperature is decreased toward the lower critical consolute temperature, the lower phase of the system water n-tetradecane + C(6)E(2) exhibits another wetting transition at the i nterface separating the upper and the middle phase. For all three syst ems-water + n-tetradecane + C(6)E(2), water + n-hexadecane + C(6)E(2), and water + n-octadecane + C(6)E(2)-the wetting transition temperatur es determined from interfacial tension measurements are consistent wit h those determined from direct contact angle measurements. In addition , experiments on the fish-shaped phase diagrams of these three systems are also performed to locate the critical end points of these systems .