Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 109: Tribology and Structure of Surfaces: Misc.
O 109.4: Vortrag
Freitag, 24. März 2017, 11:30–11:45, WIL A317
Effect of additives and external fields on lubricating properties of nematic liquid crystals — •Pritam Kumar Jana1, Wei Chen2, Mikko J. Alava1, and Lasse Laurson1 — 1COMP Centre of Excellence, Department of Applied physics, Aalto University, P.O. Box 11100, Aalto 00076, Finland — 2Computer Network Information Center, Chinese Academy of Sciences, Beijing 100190, China
Several studies have been performed to understand the structural and dynamical properties of liquid crystal lubricants under external pressure and shear stress, mainly due to the observations of ultra-low friction in such systems [1]. However, to balance between efficiency and effective cost, more extensive investigations are required. In the present study, we construct a full atomistic model where a nematic liquid crystal, 4-cyano-4-hexylbiphenyl (6CB), and a short alkane chain, hexane (C6H14), are used as lubricant and additives, respectively, and mica serves as the confining surfaces. When the sliding velocity of the upper mica plate is low enough, thin films of both pure 6CB and pure C6H14 show stick-slip dynamics. However, for the same film thickness liquid crystals exhibit higher friction as compared to hexane. In addition for thick films effective viscosities of pure liquid crystals remain constant and approximately similar to bulk viscosity. When film thickness decreases effective viscosities increase. We also consider mixtures of 6CB and C6H14, by varying their proportions, as well as the effect of external electric fields, to study the resulting lubrication properties.
[1] C. Manzato, A. S. Foster, M. J. Alava, and L. Laurson. Physical Review E 91, 012504 (2015)