Liquid Crystalline and Ionic Liquid Crystalline Lubricants

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