Liquid Crystalline and Ionic Liquid Crystalline Lubricants

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (15 October 2019) | Viewed by 14110

Special Issue Editor


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Guest Editor
Fraunhofer Institute for Mechanics of Materials IWM, Woehlerstr. 11, 79108 Freiburg, Germany
Interests: tribology; water-based lubrication; ionic liquids; programmable friction; graphene
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Special Issue Information

Dear Colleagues,

The reduction of friction and wear holds an enormous potential for resource conservation and energy saving. Holmberg and Erdemir [1] calculated that approximately 23 % of the total worldwide energy consumption is caused by friction and wear. Global savings of 1.4 % of GDP/year and 8.7 % of total energy consumption are possible through tribological optimization in the long term. Therefore superlubricity [2] and in situ control of friction [3] were identified as two of the greatest challenges in tribology. The development of novel and better base oils and additives, which has been pursued since the mid-1960s to improve tribological properties, is gradually reaching its limits. For this reason, new substances based on complex liquids, such as liquid crystals or ionic liquids, are currently becoming the focus of research.

This Special Issue addresses the tribological behavior of liquid crystals which were discovered in 1888 by the Austrian botanist F. Reinitzer. The first investigations on the friction-reducing effect of liquid crystals (LCs) were published in the 1980s. It was found that LCs are surface active with special anisotropic properties which can lead to ultralow friction. This development resulted in the ACS Symposium "Tribology and the Liquid Crystalline State" in 1990. Subsequently, a number of molecular structures were found which led to a significant reduction of friction, both in the form of pure substances or in mixtures with various oils. A review article on the research work on liquid crystals for tribological applications was published by Carrión et al. [4]. In recent years, tribological studies have also shown the potential of ionic liquid crystals as possible additives to oil or even water. In recent years, these attractive properties have led to further research in the field of tribology of LCs. However, it has been shown that not all LCs are suitable and that the manufacturing costs pose a problem to their applicability.

This Special Issue will demonstrate current advances and future trends using liquid crystals and ionic liquid crystals in the field of tribology emphasizing on the underlying friction and lubrication mechanisms. Contributions addressing the mechanisms under mild tribological conditions, as well as under high pressures and temperatures with the additional effects of tribochemical reactions are welcome.

[1] Holmberg, K.; Erdemir, A. Influence of tribology on global energy consumption, costs and emissions. Friction 2017, 5, 263–284.

[2] Hod, O.; Meyer, E.; Zheng, Q.; Urbakh, M. Structural superlubricity and ultralow friction across the length scales. Nature 2018, 563, 485–492.

[3] Fajardo, O.Y.; Bresme, F.; Kornyshev, A.A.; Urbakh, M. Electrotunable Lubricity with Ionic Liquid Nanoscale Films. Sci. Rep. 2015, 5, 7698.

[4] Carrión, F. J.; Martínez-Nicolás, G.; Iglesias, P.; Sanes, J.; Bermúdez, M. D. Liquid Crystals in Tribology. Int. J. Mol. Sci. 2009, 10, 4102-4115.

Dr. Tobias Amann
Guest Editor

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Keywords

  • Liquid crystals
  • Ionic liquid crystals
  • Lubricant additives
  • Nanofluids
  • Friction
  • Lubrication
  • Coatings
  • Tribochemistry

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Published Papers (3 papers)

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Research

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13 pages, 4042 KiB  
Article
Macroscopic Friction Studies of Alkylglucopyranosides as Additives for Water-Based Lubricants
by Wei Chen, Tobias Amann, Andreas Kailer and Jürgen Rühe
Lubricants 2020, 8(1), 11; https://doi.org/10.3390/lubricants8010011 - 16 Jan 2020
Cited by 16 | Viewed by 4115
Abstract
Water-based lubricants might become an interesting alternative to conventional oil-based lubricants and help to reduce wear as well as improve the energy efficiency of transport processes. Since pure water is generally a rather poor lubricant due to its low viscosity and corrosiveness, it [...] Read more.
Water-based lubricants might become an interesting alternative to conventional oil-based lubricants and help to reduce wear as well as improve the energy efficiency of transport processes. Since pure water is generally a rather poor lubricant due to its low viscosity and corrosiveness, it must be tribologically optimized with suitable additives. Here, we study the friction behavior of alkyl glucopyranosides (AGPs) with varying lengths of the alkyl chain. Sliding experiments show that a significant reduction in the coefficient of friction compared to that of pure water is observed. The extent of friction reduction depends strongly on the concentration and on the shearing conditions. It is assumed that the low coefficients of friction are due to the ability of AGPs to form liquid crystalline phases with an ordered structure in the friction gap. Furthermore, the interaction of the AGPs with the surface forms a wear protection layer (boundary lubrication). The friction properties of the water-based system are compared to those of a conventional, mineral oil-based lubricant. Full article
(This article belongs to the Special Issue Liquid Crystalline and Ionic Liquid Crystalline Lubricants)
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Review

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25 pages, 10678 KiB  
Review
Liquid Crystals as Lubricants
by Nadezhda V. Usol’tseva and Antonina I. Smirnova
Lubricants 2019, 7(12), 111; https://doi.org/10.3390/lubricants7120111 - 9 Dec 2019
Cited by 14 | Viewed by 5263
Abstract
The review summarizes the literature data and the authors’ own research results on the application of liquid crystals in tribology. It has been shown that both thermotropic (calamitic, discotic, cholesteric) and lyotropic (surfactants, chromonics) mesogens as tribological additives are able to optimize the [...] Read more.
The review summarizes the literature data and the authors’ own research results on the application of liquid crystals in tribology. It has been shown that both thermotropic (calamitic, discotic, cholesteric) and lyotropic (surfactants, chromonics) mesogens as tribological additives are able to optimize the properties of lubricating compositions when introduced even at low concentrations to oils and greases. A wide possibility of varying the chemical structure of mesogens and studying the relationship between their structure and tribological properties can be used for the desired (programmed) change of the quality of tribotechnical processes. The synergism of the combined use of mesogenic esters of cholesterol and carbon nanostructures as additives in improving tribological properties has been established. The use of synthetic lubricants in biological systems still requires further research as the experimental results obtained on models of joint prostheses in vitro conditions are significantly worse than the results obtained in vivo. Considering the annual loss of billions of US dollars worldwide due to the low efficiency of friction processes in the industry and the resulting wear, liquid crystals and the systems based on them can be the most effective way to optimize these processes. The present review will be useful for researchers and industrialists. Full article
(This article belongs to the Special Issue Liquid Crystalline and Ionic Liquid Crystalline Lubricants)
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9 pages, 1243 KiB  
Review
Ionic Liquid Crystals in Tribology
by M.D. Avilés, C. Sánchez, R. Pamies, J. Sanes and M.D. Bermúdez
Lubricants 2019, 7(9), 72; https://doi.org/10.3390/lubricants7090072 - 21 Aug 2019
Cited by 22 | Viewed by 4171
Abstract
The present work intends to provide a brief account of the most recent advances in the use of ionic liquid crystals (ILCs) in the field of tribology, that is, the development of new lubricants with the ability to reduce the coefficients of friction [...] Read more.
The present work intends to provide a brief account of the most recent advances in the use of ionic liquid crystals (ILCs) in the field of tribology, that is, the development of new lubricants with the ability to reduce the coefficients of friction and the wear rates of materials under sliding conditions. After a definition of ILCs and their relationship with neutral liquid crystals (LCs) and ionic liquids (ILs), the review will be focused on the influence of molecular structure and composition on the tribological performance, the combination with base oils, surfactants or water, and the different sliding configuration and potential applications. The main mechanisms proposed in order to justify the lubricating ability of ILCs will be analyzed. Special emphasis will be made for recent results obtained for fatty acid derivatives due to their renewable and environmentally friendly nature. Full article
(This article belongs to the Special Issue Liquid Crystalline and Ionic Liquid Crystalline Lubricants)
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