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

Abstract

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 bodycentred 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) diblock 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 Ia " 3d) 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.

Close-Packed Spherical Morphology in an ABA Triblock Copolymer Aligned with Large-Amplitude Oscillatory Shear

“…101 Interestingly, in soft materials which form FCC spheres, the application of shear predominantly produces a transition to the HCP spherical microstructure. 59 60,64 The alignments of the HCP and FCC spheres in our study follow the literature conventions described above: (1) closepacked planes are stacked along the shear gradient direction, (2) in the HCP structure, the velocity direction is parallel to the close-packed direction, and (3) the FCC structure is rotated 90°such that the close-packed direction is parallel to the vorticity direction (as described previously, prior studies have reported tilted or rotated FCC structures).…”

Unexpected Intermediate State for the Cylinder-to-Gyroid Transition in a Block Copolymer Solution

“…Following the temperature quench to 69 8C, the scattering pattern does not show any distinct change even 40 min after the rheometer reaches temperature equilibrium (pattern 2). The 10-spot scattering pattern characteristic of G [7,12] then appears abruptly, approximately at the same time as the elastic modulus begins to increase. The 10-spot profile continues to sharpen with time, as illustrated by pattern 3 obtained after 2 h of annealing and pattern 4 after 8 h. From comparison of the SAXS patterns and the rheology trace, the C e G transition at 69 8C appears as a one-step process, with a substantial induction time.…”

“…The four very weak second-order spots at l 60 8 relative to the equator are consistent with reflections from {220} planes. [7,12] The presence of these reflections suggests that the gyroid phase constitutes a directionally oriented polycrystal. The [111] axis lies along the shear direction z, and the {211} and {220} planes that intersect along the [111] direction are brought into the diffracting condition by rotating around this axis.…”

An integrated Couette system for in situ shearing of polymer and surfactant solutions and gels with simultaneous small angle x-ray scattering

“…[7][8][9] We have recently developed the first instrument for si-multaneous SAXS/rheology experiments on soft solids such as block copolymer melts and gels. [10][11][12][13][14][15] This instrument is based on a modified Rheometrics Solids Analyzer RSA II rheometer. The utility of the device was first demonstrated by examining the effect of shear on cubic micellar phases formed by poly͑oxyethylene͒-poly͑oxybutylene͒ ͑EB͒ diblock copolymers in aqueous K 2 SO 4 solutions.…”

“…The utility of the device was first demonstrated by examining the effect of shear on cubic micellar phases formed by poly͑oxyethylene͒-poly͑oxybutylene͒ ͑EB͒ diblock copolymers in aqueous K 2 SO 4 solutions. 10,11,14,15 We have utilized the shear sandwich geometry ͑i.e., oscillatory shearing between parallel plates͒, with apertures in the plates to allow transmission of the x-ray beam. Using this instrument, it has proved possible to correlate changes in the dynamic mechanical properties upon large amplitude shearing to changes in the alignment of the ordered microstructures.…”