[SY-O6] On the potential use of liquid crystals as ‘smart’ lubricants - an MD simulation study
Liquid crystals (LC) - well-known for their application in LC-displays - have recently raised interest also for lubrication applications: favorable friction properties (specific friction of the order 0.005) have been experimentally observed in different systems [1]. The special behavior is attributed to the anisotropic viscosity and compressibility, which LC exhibit in semi-ordered phases (i.e. nematic or smectic phase). The LC molecules' elongated shape allows them to align with the shear, which could simultaneously reduce friction and increase load support. Moreover, the complex phase behavior and dynamic properties might also be exploited to design novel tribological systems with tunable or self-regulating friction, so-called ‘smart’ lubricants [2,3].
Here, we present a molecular dynamics simulations study of different LC lubricated model tribo-systems with the aim to characterize the LC rheological properties and investigate possible tuning mechanisms on a microscopic level. Shearing simulations of LC lubricating films with different structure characteristics, i.e. preferential molecule orientation, were performed for varying loads and shear rates. The response of the systems (velocity profiles, local viscosity and shear force) was evaluated and correlated to the fluid film structure, which is influenced by the flow. Of particular interest are situations, where the inherent equilibrium structure of the LC film (induced by surface boundary conditions or external fields) is different from the shear direction, due to the competing forces for aligning the LC molecules in different directions.
[1] T. Amann, C. Dold and A. Kailer, Tribology International 65 (2013), p. 3
[2] C. Tadokoro, T. Nihira and K. Nakano, Tribol Lett 56 (2014), p. 239
[3] S. Itoh, Y. Imura, K. Fukuzawa andH. Zhang, Langmuir 31 (2015), p. 11360
Here, we present a molecular dynamics simulations study of different LC lubricated model tribo-systems with the aim to characterize the LC rheological properties and investigate possible tuning mechanisms on a microscopic level. Shearing simulations of LC lubricating films with different structure characteristics, i.e. preferential molecule orientation, were performed for varying loads and shear rates. The response of the systems (velocity profiles, local viscosity and shear force) was evaluated and correlated to the fluid film structure, which is influenced by the flow. Of particular interest are situations, where the inherent equilibrium structure of the LC film (induced by surface boundary conditions or external fields) is different from the shear direction, due to the competing forces for aligning the LC molecules in different directions.
[1] T. Amann, C. Dold and A. Kailer, Tribology International 65 (2013), p. 3
[2] C. Tadokoro, T. Nihira and K. Nakano, Tribol Lett 56 (2014), p. 239
[3] S. Itoh, Y. Imura, K. Fukuzawa andH. Zhang, Langmuir 31 (2015), p. 11360