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Tribological Aspects of Control over Frictional Interaction between Solids in the Presence of Liquid Crystals
Abstract
The development of novel additives ensuring improved performance of lubricating materials is one of the pressing problems
of modern tribological engineering. In this respect. liquid crystals (LC) have captured keen attention of tribologists due
to their unique lubricity, the experience accumulated in this sphere has proved that LC behave most efficiently as antifrictional
additives when found in the mesomorphic state.
The work presents investigation results of the mesomorphic state and lubricating action of cholestric LC distinguished by
their chemical structure and physical properties, and their mixtures with Vaseline oil. The phase slate and the phase transition
temperature of LC structures were estimated by the polarizing microscopy with application of a purposefully manufactured device.
The device is intended to visualize and perform a continuous control of phase variations in LC mixtures in response to temperature.
The tribological tests were carried out within the temperature interval 0.1÷0.5 m/s and 0.1÷3.0 MPa loads for the steel-on-steel
friction pair using a face friction machine following the disc-on-cylinder end geometry under a given test temperature.
Aggregative states of matters are governed by ratio of average kinetic energy of molecular heat motion and their potential energy. Intermolecular forces are short-term; they reveal itself at low distances comparable with molecular size, unlike the long-tern forces (gravitational, electromagnetic etc.).
We investigated the features of the optical properties of magnetoactive cholesteric liquid crystals (CLCs) in an external static magnetic field. The boundary-value problem of light transmission through a finite layer of a magnetoactive CLC at normal light incidence and light reflection from a half-space is considered. We also investigated the evolution of the reflection with a change in the azimuth and ellipticity of the incident light. Some features of the reflection spectra, optical rotation, and polarization ellipticity, as well as the ellipticity spectrum of the eigen polarizations, are investigated, too. The peculiarities of the ellipticity evolution of the eigen polarizations due to a change in the magneto-optical activity parameter are considered.
Experiments are described in which friction coefficients under boundary lubrication regime are measured with a nematic liquid crystal as the lubricant. Using steel-to-steel contacts, with one of the mating surfaces coated with a thin insulating film, electric fields are applied across the liquid crystal film. A substantial decrease in the friction coefficient is observed with both d.c. and low-frequency a.c. voltages, suggesting the possibility of controlling friction by external fields.
Orientation of Nematic Liquid Crystals and Their Mixtures (in Russian)
- Koniar Zh