B.I. Kupchinov’s research while affiliated with National Academy of Sciences of Belarus 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.

The effect of temperature in the mesomorphic condition on the lubricity of cholesteric liquid crystals is analyzed. It was established a practically linear relationship between the temperature of transition of compositions into the liquid crystalline phase and the phase of isotropic liquid. It is shown that the friction coefficient of individual cholesteric liquid crystals and their blends within the mesophase is temperature dependent and can change by an order of magnitude and has a reversible nature.

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.

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.

Comparative studies of worn surfaces lubricated by pure oils and oils with additives were conducted with use of atomic force microscope. It was established that introduction of liquid crystals or molybdenum disulfide dispersion in oil results in formation of smoothed microreliefs of similar character. Low friction coefficient and small wear, high load opacity of tribosystem, and also the formation of smaller microasperities testifies, that oil with liquid crystal additive is more effective in comparison with other lubricants.

Comparative investigations of microrelief of friction surfaces lubricated with pure oils with and without additives were conducted. With the help of atomic force microscope, it was established that introduction of liquid crystals or molybdenum disulfide dispersion into the lubricant results in formation of smoothed microreliefs of similar character. Low friction coefficient and wear, high load capacity of tribojunction and also formation of smaller microasperities when the liquid crystal additive is used makes it more effective as compared with other lubricating media.

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.