Rheology and Structures of Aqeuous Gels of Triblock (oxyethylene/oxybutylene/oxyethylene) Copolymers with Lengthy Oxyethylene Blocks

摘要

Four EBE copolymers (E=oxyethylene repeat unit,B=oxybutylene repeat unit,B=oxybutylene repeat unit)based on a B_(20) central block and end blocks ranging from 58 to 260 E units wee studied.Rheological measrueemnts (oscillatory andsteady shear) were used to confirm gelboundaries (priviously explored by a tube inversion method) and to determine storage and oss moduli (G' and G") and yield stresses (#delta#_y) for aqueous gels formed at copolymer concentrations below 20 wt%.The phase diagrams contianed a region of hard gel (G'>G",high G' and #delta#_y),an extesive region of soft gel ((G'>G",low G' and #delta#_y),denoted 1,and a second region of soft gelat low temperatures,denoted 2.Small-angle X-ray scattering was uesed 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 gelboundary was not defined,although the Im3m and Pm3n cubic structures were eliminated.Depending on concentration,the soft gels were assigned either t opercolationinduced fractalstructures (soft gel 1 ) or to defective cubic structures (soft gels 1 and 2).