Simultaneous Rheology and Small-Angle Scattering Experiments on Block Copolymer Gels and Melts in Cubic Phases

A new instrument for simultaneous small-angle X-ray scattering and rheology experiments on soft solids is described. This device is based on a commercial rheometer with a shear sandwich geometry in which the sample is subjected to a planar oscillatory deformation. This instrument has been used for time-resolved small-angle X-ray scattering/rheology experiments at the Synchrotron Radiation Source, Daresbury Laboratory, England. The focus has been in particular on the effect of large-amplitude shearing on the orientation of cubic phases in gels of block copolymers formed in concentrated solutions, and on the bicontinuous cubic phase of a block copolymer melt. Representative results are presented for face-centred cubic (f.c.c.) and body-centred cubic (b.c.c.) phases in gels of poly(oxyeth­ylene)-poly(oxybutylene) diblock copolymers, and for the bicontinuous cubic `gyroid' structure in a poly-(ethylene-alt-propylene)-poly(dimethylsiloxane) di-block copolymer melt. The orientations of the micellar b.c.c. phases in the gels and the gyroid structure (belonging to the b.c.c. space group ) following large-amplitude shearing are shown to be the same, i.e. directionally oriented crystals are produced in both cases, in which (111) directions are oriented along the shear direction.