Effect of shear on cubic phases in gels of a diblock copolymer

I.W. Hamley, J.A. Pople, J.P.A. Fairclough, N.J. Terrill, A.J. Ryan, C. Booth, G.E. Yu, O. Diat, K. Almdal, K. Mortensen, M.E. Vigild

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    The effect of shear on the orientation of cubic micellar phases formed by a poly(oxyethylene)poly(oxybutylene) diblock copolymer in aqueous solution has been investigated using small-angle x-ray scattering (SAXS) and small-angle neutron scattering (SANS). SAXS was performed on samples oriented in a Couette cell using steady shear, and SANS was performed on samples subject to oscillatory shear in situ in a rheometer with a shear sandwich configuration. A body-centered-cubic (bcc) phase observed for gels with concentrations greater than 30 wt % copolymer was found to orient into a polydomain structure, with the close-packed {110} planes both parallel and perpendicular to the shear plane. For gels with 30 wt % copolymer or less, a face-centered-cubic (fcc) phase was observed, and this was also observed on heating the more concentrated gels that formed a bcc phase at room temperature. The fcc phase could be oriented to form a highly twinned structure, with a significant deviation from the ABCABC... stacking sequence of the ideal structure due to random sequences resulting from slip of {111} hexagonal-close-packed planes. For the lower concentration gels, a transition from hard to soft gel on increasing temperature was found to be characterized by a change in the susceptibility of the sample to macroscopic shear orientation, as probed using SAXS. The hard gel could be oriented by shear into a twinned fee structure, whereas the soft gel comprised a fee phase with a small grain size, which could not be sheared to form a macroscopically oriented domain. Shear only homogenized the sample, producing a powder SAXS pattern from a fcc structure.
    Original languageEnglish
    JournalJournal of Chemical Physics
    Issue number16
    Pages (from-to)6929-6936
    Publication statusPublished - 22 Apr 1998


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