Shear induced order in SEP diblock copolymer micelles: multiple BCC slip systems

Poly(styrene-$b$-ethylene-\textit{alt}-propylene) (SEP) diblock copolymers are solvated by squalane leading to glassy poly(styrene) domains dispersed in a viscoelastic medium. For diblocks containing less than about 50{\%} by weight poly(styrene) and at SEP concentrations greater than 6 w. {\%} these mixtures self-assemble into glassy spherical microdomains that order on a body centered cubic (BCC) lattice. We have investigated how polycrystalline configurations respond to large amplitude oscillatory shear as a function of shear rate, strain amplitude and block copolymer composition. Structure was characterized by small-angle X-ray scattering measurements while simultaneously deforming the mixtures with an \textit{in-situ} rheometer. All three slip systems associated with plastic deformation in BCC metals$\{110\}<\bar {1}11>,\{211\}<\bar {1}11>,\{321\}<\bar {1}11>$, were identified with the x-ray beam oriented perpendicular to the shear plane. Higher shear rates and larger strain amplitudes produced more slip within the $\{211\}<\bar {1}11>$ system. These results represent one of the most comprehensive assessments of BCC structure in solvated copolymers and will be discussed within the context of the associated linear viscoelastic behavior.