Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 63: Polymer and Molecular Dynamics II

CPP 63.10: Talk

Thursday, March 15, 2018, 12:00–12:15, C 264

Transitions between diblock copolymer lamellar orientations in shear flow — •Ludwig Schneider and Marcus Müller — University of Göttingen, Institute of Theoretical Physics, Göttingen, Germany

Shear alignment of microphase-separated materials is a well known strategy to manipulate self-assembled samples towards macroscopic anisotropy. However, details about the exact mechanism of the reorientation towards equilibrium states, previously trapped in meta-stable states, remain an open research question.

A constant shear flow is applied to a melt of symmetric diblock copolymers. The subsequent transition between the unstable (parallel) and the stable (perpendicular) lamellar configuration is investigated. The hypothesis for the transition of an unstable lamellar grain in a stable matrix is either i) the rotation of the grain in the matrix, ii) a growth and shrink process extinguishing the unstable grain, or iii) a melting of the unstable grain with a subsequent reorientation of the stable orientation.

Using Molecular Dynamics simulation, we observe two different mechanisms as a function of shear rate: At high shear rate, none of the hypotheses apply. Instead, we observe a fast transition where the unstable grain looses its orientation order and disintegrates into a microemulsion-like state with a characteristic length scale. We believe that this scenario is realized in LAOS experiments. At low shear rate, the slow transition proceeds via the shrinking mechanism iii).