Anti-electroviscous effect of near-surface 5CB liquid crystal and its boundary lubrication property |
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Authors: | Email author" target="_blank">Xiangjun?ZhangEmail author Xiaohao?Zhang Yi?Xiong Yu?Tian Shizhu?Wen |
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Institution: | (1) State Key Laboratory of Tribology, Tsinghua University, Beijing, 100084, China |
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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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