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Flow-Induced Ordering in Cubic Gels Formed by P2VP-b-PEO-b-P(GME-co-EGE) Triblock Terpolymer Micelles: A Rheo-SANS Study
S. Reinicke, M. Karg, A. Lapp, L. Heymann, T. Hellweg, H. Schmalz:
Macromolecules, 43, 23, 10045-10054 (2010)
doi: 10.1021/ma101768b

Small-angle neutron scattering (SANS) measurements under steady shear were performed to determine the exact nature and degree of structural order within a hydrogel based on poly(2-vinylpyridine)-block-poly(ethylene oxide)-block-poly(glycidyl methyl ether-co-ethyl glycidyl ether) (P2VP56-b-PEO410-b-P(GME48-co-EGE48)) triblock terpolymer micelles. Previous static SANS measurements indicated the presence of a simple cubic (sc) or body centered cubic (bcc) packing. By exposing the sample to steady shear, different macroscopic structural transitions were induced, indicated by a stress plateau and a significant change of the 2D SANS patterns. A comparison of these 2D patterns with patterns from analogous systems reported in literature and theoretical predictions revealed the presence of a bcc structure. Furthermore, with increasing shear rate the structural alignment changes from a nonoriented state to an intermediate state consisting of polycrystalline bcc domains with weak preferential orientation, and finally to a highly aligned state in which twinned bcc domains exist. The [111] axis of the twinned bcc crystals is aligned in the direction of the shear flow, and the {110} slipping planes are preferentially aligned parallel to the shear plane (walls of the Couette cell). A minor fraction of twinned bcc domains, probably located in regions of lower shear velocity, i.e., close to the inner wall of the Couette cell (stator), is tilted by an angle of 90° with respect to the shear plane.


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