RELAXATION AND DIELECTRIC PROPERTIES OF LUBRICANT COMPOSITIONS BASED ON LITOL-24 WITH MESOGENIC ADDITIVES

In order to improve the wear resistance of machine parts in industry and agriculture, the various synthetic lubricants with mesogenic additives are used. It is established that adding an additive to the base lubricant leads to a decrease in the friction coefficient and a decrease in the wear of the machine parts. Such multi-component systems, lubricants and additives, are lyotropic liquid crystals (LC) and exhibit rich mesomorphism which also affects their tribological characteristics. The composing of phase diagrams of LC lubricants with additives depending on the concentration and thermodynamic quantities is an important research task in connection with the need to optimize the composition of lubricants and to determine the regimes of their most effective employment. In this regard, in addition to mechanical testing of specimens in the presence of lubricant compositions, it is necessary to study the physicochemical properties and carry out structural studies of multicomponent lubricants. We were motivated by the possibility to complement the existing data on the optical and X-ray spectroscopy, electron microscopy and theoretical studies of the thermodynamic parameters of lubricant composites by dielectric spectroscopy (DE). Using the method of DE spectroscopy, we first investigated the electrical properties of lubricating compositions based on Litol’s-24 comprising mesogenic additives as homologues carboxylates of copper (II), valerate and isovalerate copper in the concentration range 1, 5, 10 and 20 wt. %. We found the frequency dependence of the dielectric permeability, conductance, dielectric loss, as well as the temperature and concentration dependence of the electrical quantities of lubricant compositions in the measuring electric field of the frequency range 100 Hz – 1 MHz and at heating from room temperature to temperatures exceeding Litol’s-24 melting temperature. The paper confirms the possibility of the occurrence of phase transitions between the columnar and isotropic liquid-crystalline phases at the concentrations of additives of 1, 5 and 10 wt. %, and estimates the activation energies of the lubricant compositions in order of magnitude. The obtained results are applicable for the analysis of tribological characteristics of lubricant compositions.

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