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Observation of shear-induced nematic–isotropic transition in side-chain liquid crystal polymers

Nature volume 409, pages 167–171 (2001)Cite this article

Abstract

Flow-induced phase transitions are a fundamental (but poorly understood) property of non-equilibrium systems, and are also of practical importance for tuning the processing conditions for plastics, petroleum products, and other related materials21. Recognition that polymers may exhibit liquid crystal properties has led to the discovery of the first tailored side-chain liquid crystal polymers (SCLCPs), which are formed by inserting a spacer between the main polymer chain and the lateral mesogen liquid–crystalline graftings22. Subsequent research has sought to understand the nature of the coupling between the main polymer chain and the mesogens, with a view to obtaining better control of the properties of these tailored structures22. We show here that the parallel or perpendicular orientation of the mesogens with respect to the main chain can be reversed by the application of an external field produced by a shear flow, demonstrating the existence of an isotropic nematic phase transition in SCLCPs. Such a transition, which was theoretically predicted1,2 for low-molecular-weight liquid crystals but never observed, is shown to be a general property of SCLCPs too. We expect that these SCLCPs will prove to be good candidate systems for the experimental study of these non-equilibrium phenomena.

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Figure 1: Behaviour of the side-chain liquid crystal polymer described in the text.
Figure 2: Evolution of the birefringence versus shear rate at different temperatures.
Figure 3: Stress versus shear rate at 117.5 °C measured in a cone-plate cell (diameter: 12 mm, angle: 0.17 rad) in controlled shear rate mode.
Figure 4: Anisotropy of the main-chain conformation as revealed by neutron scattering.

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Acknowledgements

We thank P. Baroni for the construction of the shear devices and his technical help during the experiments.

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  1. Laboratoire Léon Brillouin (CEA-CNRS), Gif-sur-Yvette Cédex, Ce-Saclay, 91191, France

    Caroline Pujolle-Robic & Laurence Noirez

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  1. Caroline Pujolle-Robic
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  2. Laurence Noirez
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Correspondence to Laurence Noirez.

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Pujolle-Robic, C., Noirez, L. Observation of shear-induced nematic–isotropic transition in side-chain liquid crystal polymers. Nature 409, 167–171 (2001). https://doi.org/10.1038/35051537

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