Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: POSTERS Driven Soft Matter

CPP 20.1: Poster

Wednesday, February 27, 2008, 16:00–18:30, Poster A

Alignment of microphase separated block-copolymers by ionic polarization — •Peter Kohn, Klaus Schröter, and Thomas Thurn-Albrecht — Department of Physics, Martin Luther University Halle-Wittenberg, 06120 Halle, Germany

Microphase separated block-copolymers display well defined local periodic structures. In the absence of an external field the domains are oriented isotropically on a macroscopic scale. It is well known that by applying a static external electric field, which couples to the dielectric contrast of the domains, the system’s thermodynamic equilibrium is changed to the state where the domain interfaces are oriented along the electric field direction.
In contrast to this approach we show that alignment can also be achieved with AC-electric fields which induce an additional polarization caused by mobile ions in a system with selective ion solubility in one block. In such a dissipative conducting system the resulting structure is governed by stability considerations rather than thermodynamic equilibrium, but an orientation of the interfaces parallel to the field is the stable domain-orientation with no torque acting on the domains. We use impedance spectroscopy to characterize the induced ionic polarization in a styrene-methylmethacrylate block-copolymer doped with lithium triflate. By small-angle x-ray scattering the effect of electric fields of different frequency and strength on the domain orientation is studied. Orientation based on mobile ion polarization is more efficient than the dielectric mechanism of orientation.