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Anti-electroviscous effect of near-surface 5CB liquid crystal and its boundary lubrication property

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Abstract

The rheological properties of the near-surface 5CB (4-pentyl-4′-cyanobiphenyl) liquid crystal (LC) under an external electric field (EEF) are investigated using a dynamic quartz crystal microbalance (QCM). The real-time film-forming process and shearing response of the EEF-induced absorbed LC liquid are studied. The results indicate that the EEF-induced adsorbed LC is composed of a bulk liquid layer and a near-surface boundary layer. Within the boundary layer, the nematic 5CB LC presents an anti-electroviscous effect which may be due to the EEF-induced ordered structure. According to the estimation from QCM measurements, this near-surface layer is about 100 nm thick under certain electric strength and is irreversible even after the EEF is removed. Based on a QCM model, the near-surface LC layer presents a decreased and irreversible viscosity as the EEF voltage increases against the reversible electro-viscous effect of the bulk 5CB liquid crystal measured by rheometer and Raman spectrum measurements. The anti-electroviscous effect of the near-surface 5CB layer is also proved by an improved boundary lubrication property tested on a tribometer. The coefficient of friction of 5CB LC after a preliminary induction of EEF is the lowest one compared to those without EEF and during the application of EEF. The unique anti-electroviscous property of near-surface 5CB LC revealed in this article suggests a potential method to actively reduce shear resistance in boundary lubrication and in microfluidics.

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Acknowledgements

The authors would like to thank NSFC for the financial support under grant numbers of 50730007, 50975154, as well as the National Key Basic Research Program of China (Grant No 2007CB607604).

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Authors and Affiliations

  1. State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China

    Xiangjun Zhang, Xiaohao Zhang, Yi Xiong, Yu Tian & Shizhu Wen

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  1. Xiangjun Zhang
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  2. Xiaohao Zhang
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  3. Yi Xiong
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Correspondence to Xiangjun Zhang.

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Zhang, X., Zhang, X., Xiong, Y. et al. Anti-electroviscous effect of near-surface 5CB liquid crystal and its boundary lubrication property. Rheol Acta 51, 267–277 (2012). https://doi.org/10.1007/s00397-011-0607-5

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  • DOI: https://doi.org/10.1007/s00397-011-0607-5

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