A STUDY OF LYOTROPIC MESOPHASES OF CONCENTRATED-SOLUTIONS OF A TRIBLOCK COPOLYMER OF ETHYLENE-OXIDE AND 1,2-BUTYLENE OXIDE, E16B10E16, USING RHEOMETRY, POLARIZED-LIGHT MICROSCOPY, AND SMALL-ANGLE X-RAY-SCATTERING

The phase behavior and structure of aqueous solutions of a triblock co polymer of ethylene oxide and 1,2-butylene oxide, E16B10E16, have been studied as a function of polymer concentration (5-75 wt %) and temper ature (5-95 degrees C) using tube inversion, rheometer, polarized ligh t microscopy, and small-angle X-ray scattering. Sol-gel and gel-sol bo undaries were determined by rheometry and tube inversion methods. Pola rized Light microscopy and small-angle X-ray scattering were used to i dentify the lyotropic phases. A hexagonal mesophase was found for the stiff gel region (40-52 wt %). A lamellar phase was located in the gel s of concentrated solutions (greater than or equal to 54 wt %) by usin g polarized light microscopy and small-angle X-ray scattering. Further more, solutions with lamellar structure were detected by small-angle X -ray scattering for the mobile phases of the concentrated solutions (> 44 wt%). Small-angle X-ray experiments also showed that the concentrat ed cloudy sols (>40 wt%) at high temperature had aggregates with lamel lar structure. Two soft gel regions were defined: the soft gel region I concerning the interaction of spherical micelles, which was only det ected with a rheometer, was found at moderate concentrations (20-40%), and the soft gel region II concerning the arrangement of rodlike mice lles, which was defined with a rheometer and also the tube inversion m ethod, was found in the concentration region 40-49 wt % before the for mation of the hard gel. The transition of spherical micelles to rodlik e micelles was also investigated by rheometer at high temperatures for low concentrated solutions. The detailed phase diagram from 5 to 75 w t % solutions of the copolymer is presented.