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Molecular manipulator driven by spatial variation of liquid-crystalline order

Nature Materials volume 9, pages 816–820 (2010)Cite this article

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Abstract

Collective long-range interactions between micrometre-sized impurities in liquid crystals result from the elastic distortion of the liquid-crystalline order1,2,3,4,5,6,7,8. For substantially smaller polymeric impurities, what is relevant is not the elastic interaction between them but the coupling between the scalar nematic order parameter S and the polymer concentration φ. This coupling originates from local molecular interactions, but becomes long ranged because the total polymer concentration is conserved over the whole sample. Here, we propose a new mechanism by which the spatial variation of S generates a force, mediated by the coupling between S and φ, that transports nanoscale polymeric impurities. We have designed a prototype of a molecular manipulator that moves molecules along spatial variations of the scalar order parameter, modulated in a controlled manner by spot illumination of an azobenzene-doped nematic phase with ultra-violet light. We also demonstrate the use of the manipulator for the measurement of the anisotropic diffusion constant of a polymer in the nematic phase. The manipulator can control the spatial variation of the polymer concentration, thus showing promise for use in the design of hybrid soft materials.

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Figure 1: Spatial variation of the scalar order parameter and the excess polymer concentration before and after ultraviolet irradiation.
Figure 2: Excess birefringence δ na and ultraviolet-irradiation time dependencies of the excess fluorescence intensity δA.
Figure 3: Anisotropic diffusion of accumulated polymers in the nematic phase after switching off the ultraviolet irradiation.

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Acknowledgements

The authors are very grateful to S. Ujiie for providing the azobenzene derivatives and to J. Lagerwall for his kind proofreading and helpful comments on this manuscript. This work was partly supported by a Grant-in-Aid for Scientific Research on Priority Area ‘Non-equilibrium soft matter physics’, a Grant-in-Aid for Scientific Research (A) (No. 18204037), a Grant-in-Aid for Young Scientists (B) (No. 21740312), a Grant-in-Aid for the Global COE Program ‘The Next Generation of Physics, Spun from Universality and Emergence’ from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, the Toray Science Foundation and the Murata Science Foundation.

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  1. Sadaki Samitsu

    Present address: Present address: Functional Thin Films Group, Organic Nanomaterials Center, National Institute of Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan,

Authors and Affiliations

  1. Division of Physics and Astronomy, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan

    Sadaki Samitsu, Yoichi Takanishi & Jun Yamamoto

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  1. Sadaki Samitsu
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Contributions

J.Y. conceived the initial idea. S.S. designed and conducted the experiments and analysed the results. Y.T. advised on the experiments. All authors discussed the results and implications, and wrote and commented on the manuscript at all stages.

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Correspondence to Sadaki Samitsu or Jun Yamamoto.

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The authors declare no competing financial interests.

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Samitsu, S., Takanishi, Y. & Yamamoto, J. Molecular manipulator driven by spatial variation of liquid-crystalline order. Nature Mater 9, 816–820 (2010). https://doi.org/10.1038/nmat2853

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