Shear-Induced Orientational Transitions in the Body-Centered Cubic Phase of a Diblock Copolymer Gel

Abstract

Gels of a poly(oxyethylene)−poly(oxybutylene) diblock copolymer in aqueous solution forming a bcc phase have been examined using small-angle X-ray scattering (SAXS) with simultaneous rheology. Application of large amplitude oscillatory shear is observed to induce macroscopic alignment of twinned bcc crystals. Alignment at relatively low frequency leads to a structure in which {200} planes are oriented normal to the shear direction. At high frequency, large amplitude shearing leads to a transition to flow with the [111] plane parallel to the shear direction. Flow occurs in the {110} and {211} planes which intersect along the same [111] direction, leading to a high-symmetry SAXS pattern with numerous sharp reflections. These results highlight the similarity between the defect mechanics of cubic phases in block copolymer gels and those in metals.

Poly(N-isopropylacrylamide) nanocrosslinked by polyhedral oligomeric silsesquioxane: Temperature-responsive behavior of hydrogels

“…PNI-PAM hydrogels can exhibit a clear volume phase transition in response to external stimuli such as temperature [5,6,8,17], pH [17][18][19], composition of solvents [5,9,[20][21][22][23], salt concentration [10,19], light [7,24], mechanical stress [25,26], and magnetic field [27,28], which endows the materials with many potential applications. Nonetheless, conventional hydrogels possess some drawbacks of properties [29][30][31][32][33][34][35]. For instance, organic hydrogels often display morphological inhomogeneity, low mechanical strength, low swelling ratio at equilibrium and slow swelling (and/or deswelling) rates [26,[35][36][37][38].…”

Phase behavior of block co-poly(ethylene oxide–butylene oxide), E18B9 in water, by small angle neutron scattering

“…A considerable body of work has been carried out on block copolymers in solution via time resolved scattering 0021 techniques (SAXS and SANS) [7][8][9][10][11][12][13]. This is a reliable way of determining the mesophase morphology and has been carried out by Fairclough and co-workers [8] for the diblock copolymer E 41 B 8 , where a phase diagram was constructed by SAXS measurements that displayed strong agreement with rheological data.…”

Three‐dimensional crystallographic determination of the body‐centered‐cubic morphologies of shear‐aligned block copolymer systems

“…The shear‐dependent texture of cubic bcc‐ordered block copolymer and colloidal structures has been addressed in a number of studies 2–17. However, both the observed alignment and the interpretation of apparently equal scattering patterns differ significantly from one study to another.…”