Shape and chirality transitions in off-axis twist nematic elastomer ribbons

Yoshiki Sawa, Kenji Urayama, Toshikazu Takigawa, Vianney Gimenez-Pinto, Badel L. Mbanga, Fangfu Ye, Jonathan V. Selinger, and Robin L. B. Selinger

Phys. Rev. E 88, 022502 – Published 8 August 2013

Abstract

Using both experiments and finite element simulations, we explore the shape evolution of off-axis twist nematic elastomer ribbons as a function of temperature. The elastomers are prepared by cross-linking the mesogens with planar anchoring of the director at top and bottom surfaces with a 90 $^{o}$ left-handed twist. Shape evolution depends sensitively on the off-axis director orientation at the sample midplane. Both experiments and theoretical studies show that when the director at midplane is parallel to either the ribbon's long or short axes, ribbons form either helicoids or spirals depending on aspect ratio and temperature. Simulation studies show that if the director at midplane is off-axis, ribbons never form helicoids, instead evolving to distorted spiral shapes. Experimental studies for two samples with off-axis geometry show agreement with this prediction. Samples in all these geometries show a remarkable transition from right- to left-handed chiral shapes on change of temperature. Simulations predict off-axis samples also change their macroscopic chirality at fixed temperature, depending on the angular offset. These results provide insight into the mechanisms driving shape evolution and macroscopic chirality, enabling engineering design of these materials for future applications.

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Received 6 March 2013

DOI:https://doi.org/10.1103/PhysRevE.88.022502

Authors & Affiliations

Yoshiki Sawa^*, Kenji Urayama^†, and Toshikazu Takigawa

Department of Material Chemistry, Kyoto University, Kyoto 615-8510, Japan

Vianney Gimenez-Pinto^*, Badel L. Mbanga^‡, Fangfu Ye^§, Jonathan V. Selinger, and Robin L. B. Selinger^∥

Liquid Crystal Institute, Kent State University, Kent, Ohio 44242

^*Y.S. and V.G.-P. contributed equally to this work.
^†Author to whom correspondence may be addressed: urayama@kit.ac.jp; Current address: Kyoto Institute of Technology, Department of Macromolecular Science and Engineering, Sakyo-ku, Kyoto 606-8585, Japan.
^‡Current address: Physics Department, Tufts University, Medford, MA 02155.
^§Current address: Laboratory of Soft Matter and Biological Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
^∥Author to whom correspondence may be addressed: rselinge@kent.edu.

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Vol. 88, Iss. 2 — August 2013

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