V.G. Rodnenkov’s research while affiliated with Belarusian State University of Transport and other places

Studies have demonstrated the effect of liquid-crystal additives on the tribological properties of fluoroparaffins serving as ski greases. It is established that the introduction of these additives into the HF80 grease reduces the friction coefficient considerably (3–7 times) when in contact with snow in temperatures below zero (−15°C) in the laboratory conditions. This is due to the drop in heat conductivity of the modified grease, because the orienting effect of the liquid-crystal molecules produces an anisotropic structure in the acquired lubricating layer. The effectiveness of the studied mesogenic modifiers depends on their molecular structure and concentration in the grease.

The method of microadhesiometery is used for an estimation of adhesive ability of ski ointments alloyed by mesogene substances. The opportunity of decrease in adhesive activity of ski ointment was established at the certain concentration of mesogene additive. It was proposed to use mesogene substances for decrease in adhesion of ski ointments to snow.

Different alternatives of internal friction between layers of a liquid are described. Main classes of materials capable to reduce intraliquid pressure are considered. Their advantages and disadvantages are revealed. It is recommended what materials to select as reagents reducing intraliquid friction.

Results of experimental studies of the abnormally low friction of natural joints are discussed. Methods of physical, chemical analyses have revealed a new feature of the synovial fluid in joints showing that it is capable to retain liquid crystalline cholesterol compounds. These compounds in the zone of friction of the joint cartilage produce a liquid crystalline nematic phase within the range of physiological temperatures. Tribological tests of natural and pseudosynovial fluids have revealed that low friction of the contacting cartilage is due to the liquid crystalline phase in the synovia.

The molecular structure influence of cholesterol n-alkanoates introduced in Vaseline oil on the corrosion resistance of the steel friction surface was studied. The cholesterol n-alkanoates used as antifriction additives to Vaseline oil affected the energy state of the steel 08 K∏ surface forming after friction in the given lubricants. Friction in the presence of the oil containing cholesterol n-alkanoate with the alkyl radical consisting of eight carbon atoms facilitated formation of the metal surface layer on the friction surface that possessed lower corrosion activity (low defect density) at the steady-state potential and higher activity to cathode reduction of hydrogen at the potentials differing from the steady-state one. In oils containing other cholesterol n-alkanoates on the friction surface, the above structure was not formed. The activity of the steel surface after friction to anodic dissolution at the potentials different from the steady-state one was independent of the molecular structure of cholesterol n-alkanoates.

Experimental results have shown that the tribological behavior of liquid crystalline cholesterol n-alcanoates (CA) correlates with their molecular structure. It has been revealed that the solubility of CA in Vaseline oil decreases as the alkyl radical becomes longer, meanwhile the system becomes more viscous. The lubricity of pure CA depends on their molecular mass. The increase in length of the CA alkyl radical results in the decrease in the wire drawing stress and the increase in the wear scar diameter. An inverse correlation has been established between the wire drawing stress and the CA melting enthalpy. After the introduction of CA the load-carrying capacity and the friction coefficient in oils depend on the temperature of transition into the isotropic phase. The friction coefficient tends to decrease and the load-carrying capacity increases as the temperature of the phase transition rises.

This investigation was devoted to the study of a natural phenomenon-low friction in living joints-and development of synthetic lubricants. The experiments conducted allowed us to establish that the known property of synovia to ensure the high antifrictional ability of joint cartilages is provided by the realization of a liquid-crystalline state of the lubricant in the friction zone that was unknown before. An idea was advanced that molecules of liquid-crystalline cholesterol compounds found in synovia are arranged with their longer axis aligned with prevailing microgroove locomotions on cartilage surfaces to make a liquid-crystalline nematic phase, thus reducing energy dissipation during relative motion of contacting cartilages and leading to the medicative effect revealed by experimentation.

Applications of liquid crystals in various real friction units are described and their effectiveness as components of water- and oil-based coolant-lubricants is demonstrated. Liquid crystals reduce the run-in period of internal combustion engines and manifest high wear resistance. Applications of liquid crystals for correction of human articular pathologies are illustrated.

The paper reviews the studies of the tribological behavior of oils modified by liquid crystals, specifically the solubility of liquid crystals in mineral and synthetic oils and the rheological properties of the latter. It is demonstrated that liquid crystals, irrespective of their type, improve the antifrictional behavior of oils. A relationship has been established indicating that the molecular structure of oils with these additives governs their lubricating action. The concentration of a liquid crystal additive in oil determines the moment of coefficient of friction decrease and roughness decrease.

A review of researches belonging to studying the liquid crystals properties is presented. It is shown that the liquid crystals and their mixtures as lubricants exhibit lower friction as compared with commercial oils independent of geometry and material of the friction pair. Low dissipation of the liquid crystals in the lubricating layer is provided preferably by the homeotropic orientation of their molecules.