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Tribology Letters (2018) 66:68
https://doi.org/10.1007/s11249-018-1020-3
ORIGINAL PAPER
Ultralow Friction Between Steel Surfaces Achieved by Lubricating
with Liquid Crystal After a Running-in Process with Acetylacetone
Hui Chen
1
· Chonghai Xu
1,2
· Guangchun Xiao
2
· Zhaoqiang Chen
2
· Mingdong Yi
2
Received: 7 February 2018 / Accepted: 23 April 2018 / Published online: 30 April 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
A suitable running-in process is advantageous for reducing friction. The aim of the present work was to study the influence
of the running-in with acetylacetone on tribological performance of 4-Cyano-4’-pentylbiphenyl (5CB) liquid crystal. Friction
tests were performed between steel surfaces in a ball-on-disk sliding system. After a running-in period of 240 s, the COF of
5CB was measured to be 0.013, which is about a quarter of the value (0.055) without running-in. The reduced contact pres-
sure, caused in running-in process, does not directly lead to a drop in COF. The generation of tris(acetylacetonato) iron(III)
induced by the tribochemical reactions between acetylacetone and steel surfaces, and the unique physical properties of liquid
crystal are assumed to be reasons for the ultralow COF. Surface analysis was performed to correlate COF with the topography
of wear surfaces. An evenly distributed specific grooved structure observed on wear area of the ball may have a beneficial
effect on COF as well. We believe our findings can provide an effective and simple solution to reduce COF of liquid crystal
between steel surfaces. A better understanding of the tribological behavior is needed for the development of this tribological
system and for the possible future applications.
Keywords Ultralow friction · Liquid crystal · Acetylacetone · Running-in
1 Introduction
Friction occurs in almost all mechanical devices and a large
amount of energy is consumed due to friction between
moving components. Additionally, friction causes wear and
eventually failure of machinery components. It is estimated
that 26.56 EJ energy (up to 32% of the energy) is consumed
by friction in road vehicles annually [1] and about 23%
(119 EJ) of the world’s total energy consumption originates
from tribological contacts [2]. It is expected that by taking
advantage of new technologies in surface, materials, and
lubrication, energy losses due to friction and wear could
potentially be reduced by 40% in 15 years [2]. To achieve
this goal, extensive research has been devoted to reduce the
friction and wear between moving parts. In these studies,
the tribological performance of liquid crystals (LCs) [3]
and other new type of lubricants [4, 5] are of great interest
because of their encouraging lubricating properties.
LCs exhibit mesophase between liquid and crystal phase
within a certain range of temperatures (for thermotropic
LCs) or concentrations (for lyotropic LCs). Within these
ranges, LCs exhibit the fluidity of liquids and anisotropy of
crystal in their physical properties [6]. LCs are commonly
used in flat-panel electric displays [7], but researchers have
been investigating their tribological behavior since 1980s
[8]. LCs have demonstrated unusual lubricating properties
when used as lubricants [9–12] or additives [13–16] due to
its ordered state. A review on the tribological performance
of LCs is given in the work of Carrión et al. [3]. Compared
to conventional lubricants, LCs exhibit lower coefficient of
friction (COF) and higher load-carrying ability in a lot of
studies. For instance, Fischer et al. [9] investigated the lubri-
cation of octylcyanobiphenyl (8CB, a thermotropic smectic
LC) in a thrust bearing and in ball-on-flat contact. The 8CB
presents higher load-carrying ability and lower COF com-
pared to the Newtonian fluid (S150N and S600N). Similarly,
LCs (cyanobiphenyl, 5CB, and cyanophenyl cyclohexyl,
5CPC) show a lower COF compared to other synthetic oils
* Chonghai Xu
xch@qlu.edu.cn
1
School of Mechanical Engineering, Shandong University,
Jinan 250061, People’s Republic of China
2
School of Mechanical and Automotive Engineering, Qilu
University of Technology (Shandong Academy of Sciences),
Jinan 250353, People’s Republic of China
@Phil_Robichaud
@deepthiw
@JoseServera