Abstract
Four EBE copolymers (E = oxyethylene repeat unit, B = oxybutylene repeat unit) based on a B20 central block and end blocks ranging from 58 to 260 E units were studied. Rheological measurements (oscillatory and steady shear) were used to confirm gel boundaries (previously explored by a tube inversion method) and to determine storage and loss moduli (G‘ and G‘ ‘) and yield stresses (σy) for aqueous gels formed at copolymer concentrations below 20 wt %. The phase diagrams contained a region of hard gel (G‘ > G‘ ‘, high G‘ and σy), an extensive region of soft gel ((G‘ > G‘ ‘, low G‘ and σy), denoted 1, and a second region of soft gel at low temperatures, denoted 2. Small-angle X-ray scattering was used to probe the hard gel structure. Concentrated aqueous gels (20 wt %) had a body-centered cubic (bcc, Im3m) structure. The structure of dilute gels near to the hard gel boundary was not defined, although the Im3m and Pm3n cubic structures were eliminated. Depending on concentration, the soft gels were assigne...
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