CHARACTERIZATION OF A POLY(ETHYLENE OXIDE) POLY(PROPYLENE OXIDE) TRIBLOCK COPOLYMER (EO(27)-PO39-EO(27)) IN AQUEOUS-SOLUTION

We have studied the poly(ethylene oxide)-poly(propylene oxide) tribloc k copolymer (EO(27)- PO39-EO(27)) in aqueous solution in a wide range of temperatures and concentrations. In this paper we present a phase d iagram which is based on small-angle X-ray scattering, ultrasonic spee d measurements, differential scanning calorimetry, low-shear viscosime try, and light transmission measurements. We find a broad transition f rom unimers to micelles with increasing temperatures. The micelles hav e close to spherical symmetry with a core-shell structure and an outer layer that can be described as a star micelle. The micelles grow in s ize with temperature, and phase separation with clouding takes place a t temperatures above 85 degrees C. A stiff gel is found at concentrati ons above 24% (w/w).