Lubrication by a Smectic Liquid Crystal

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Abstract
The hydrodynamic aspects of lubrication by the smectic A liquid crystal octylcyanobiphenyl (8CB) were investigated in a thrust bearing and in the concentrated ball-on-flat contact. Both bearings were run with a Newtonian mineral basestock for comparison and performed as expected; friction followed the Stribeck curve in the thrust bearing and the film thickness increased with (velocity)2/3 in the elastohydrodynamic lubrication of the point contact. The lubricating behavior of the smectic liquid crystal is qualitatively different from that of the Newtonian fluid. Curves of friction coefficient vs velocity × viscosity/load cannot be superimposed to form a Stribeck curve. The higher the load, the lower the velocity at which low friction is maintained, which is opposite to the behavior of Newtonian fluids. In concentrated contact (EHD lubrication) the smectic gives a friction coefficient that is constant with velocity and lower than the minimum value with the Newtonian fluid. The fluid film thickness varies with (velocity)½.

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