Spontaneous Change in Effective Viscosity of a Liquid Crystal by Surface Anchoring in an EHD Contact

The optical film thicknesses of a 0.1 mass% solution of hexadecanoic acid (HDA) in a nematic liquid crystal (i.e., 4-pentyl-4′-cyanobiphenyl (5CB)) were measured in an EHD contact by using ultrathin-film interferometry. Comparing with a 0.1 mass% solution of HDA in an ordinary isotropic liquid (i.e., polyalphaolefin), the optical film thickness of the solution was increased at middle entrainment speeds (i.e., in the mixed lubrication regime). This shows that the effective viscosity of 5CB was increased with decreasing the entrainment speed, by the surface anchoring of 5CB on the boundary films formed by HDA. Using this spontaneous change in the effective viscosity, it is believed that a smart lubrication system can be realized, which optimizes the viscosity of a liquid crystal lubricant autonomously so that the friction coefficient is minimized when the entrainment speed is changed. It should be noted that this method does not need any pretreatments of contact surfaces and any external fields (e.g., an electric field or magnetic field).