V.A. Levchenko

Specific heat of a liquid mixture near the consolute point in the bulk phase and in a porous medium

The critical behavior of the specific heat of the mixture 2.6-lutidine+water near the consolute point was investigated in the bulk phase and in a porous medium. The measurements of the bulk specific heat yield a critical exponent α=0.111±0.018 and a universal amplitude ratio A−/A+=1.77, in good agreement with theoretical predictions. Using previous experimental data for nitroethane+isooctane, we also determined the two-scale-factor ratio X+=0.271 between the critical amplitude of the specific heat and of the correlation length in agreement with the results reported for other fluid systems. The specific heat in the porous medium with a pore size of about 100 nm was measured. The behavior of the specific heat differs from that of the bulk specific heat. This may be the result of finite size effects, of a wetting layer in the pores, and of a distortion of the coexistence curve.

ORIENTATION ORDERING OF BOUNDARY LAYERS AND LUBRICITY OF OILS

A computer model of the adsorption process of lube oil molecules on friction surfaces reveals that carbon monocrystalline coatings with a strongly orientating effect promote the level of molecular orientation in boundary layers contrary to the amorphous ones because there is no essential orientating effect on these layers. The results of lab tribological tests of carbon coatings deposited on steel surfaces in some model oils corroborate that the coatings with a higher level of orientation ability yield better lube properties.

Influence of carbon coatings on lubricating properties of boundary layers

Abstract The friction behaviours of two types of diamond-like carbon coating (amorphous and monocrystalline) were studied under boundary lubrication. As lubricants, liquid paraffin with and without surfactant additives (stearic and oleic acids) were used as well as base mineral oil with viscosity corresponding to SAE 30. Tests were conducted on a ball-on-disc tribometer and on a tribometer where two rings were rubbing against each other. It was found that in all types of test the monocrystalline coating ensures minimal values of friction coefficient in a wider range of temperatures, whereas the amorphous coating has maximum values of friction coefficient compared with the monocrystalline coating and with the reference uncoated steel pair. This effect takes place for all lubricants studied. The observed experimental data can be explained by the strong orienting effect of the monocrystalline carbon coating on the structural order of molecules in boundary layers and correspondingly on their lubricating ability. The effect of the amorphous coating on molecular orientation in boundary layers is rather poor.

Epitropic liquid crystals — a new liquid phase

Abstract We review modern research for liquids forming epitropic liquid crystals (ELC) adjacent to walls. We consider the structure and various properties which differ from those of traditional nematic liquid crystals, such as the structural order parameter, the limited space, and the formation mechanism. The special methods and the results of these investigations are discussed in detail. An analysis of ELC layers is given (structure and influence of various affecting factors). It is shown that epitropic liquid crystals are formed by various polar organic liquids with molecules containing substituted benzene rings. It is established that in the epitropic liquid crystal layers, that is in the epitropic mesophases, there exists a secondary orientational order transition. The width of this layer and the molecular orientation depend on the dipole-dipole forces, the specific interaction with the solid substrate, and the dispersion forces of the liquid. We discuss the status and the outlook of recent experimental and theoretical work and conclude with a few remarks concerning the application of ELC layers in electronics, lubrication, tribology, and the biology of human organs.

Effect of orienting coatings on the apparent activation energy of boundary film destruction

The apparent activation energy of seizure in boundary lubrication was calculated using the temperature-kinetic approach to the description of boundary lubrication. The tests were carried out with the ball-on-disc machine. The ball was made of chromium ball-bearing steel and the disc was made of stainless steel. Discs made of stainless steel coated with aluminum nitride and high-ordered polycrystalline carbon were also used. The pair was lubricated with model lubricants. It was shown that the apparent activation energy of seizure in friction against steel coated with carbon is by almost an order of magnitude higher than in friction against uncoated steel.

Hard carbon coatings and boundary lubrication of steel parts

It is shown that the composition and structure of diamond-like carbon coatings deposited on friction surfaces of steel parts of lubricated friction units have a substantial effect on the degree of the orientation of molecules of a lubricant in a boundary film and, therefore, on the antifriction behavior of the lubricant under boundary lubrication conditions. We present the results of research carried out in recent years at the Department of Friction, Wear, and Lubrication of the Blagonravov Institute of Machine Science of the Russian Academy of Sciences in collaboration with the Chemical Faculty of the Lomonosov Moscow State University and the 25th State Research Institute of the Ministry of Defense of the Russian Federation in order to enhance the lubricity of oils, as well as to simplify and cheapen their compositions, which is of great importance from the viewpoint of ecology.

Effect of structure and composition of solid carbon coatings of steel parts on the lubricating properties of synthetic oil

The authors studied the friction and wear properties of PAOM-4 synthetic oil under the friction of steel samples, the working surfaces of which are coated by a thin layer of hard carbon coatings of different composition and structure. It was found that some of them result in improved antiwear and antifriction behavior of the test oil. The polyalphaolefin oil shows the highest lubricity when steel rubs against carbon diamond-like coatings, namely, monocrystalline tungsten-alloyed coatings and amorphous coatings with increased sp3 phase.

Laboratory tribotests of thin carbon coatings in lubricants

The basic means and methods for tribotests of modern thin coatings in lubricants are considered. The ball-on-disk, cylinder-on-plane, and ring-on-ring arrangement are used.

Nanostructured carbon coating-orientant and its interaction with boundary lubricating layers

In previous works we have shown that to improve oil lubricity one should increase the orientability of the working surfaces of solid bodies. This can be achieved by applying special carbon orientant coatings to ensure the formation of highly oriented boundary layers whose molecules acquire some orientation under the effect of the solid-phase force field. The level of the orientation effect and coating characteristics are dependent on its synthesis parameters, which makes it possible to regulate them during coating application. It is shown that with increasing structural ordering of the boundary layers, the friction coefficient decreases, thus widening the limits of resistance to temperature. In contrast, tribological tests of traditional carbon coatings of the amorphous structure are devoid of the above-described effect. The estimate of the total activation energy of failure of the boundary layers for steel samples with a polycrystalline coating-orientant has proved this value to be much higher than for the same steel with a coating without the orientant coating properties.

Orientational ordering in 2,6-lutidine near quartz surfaces modified by carbon

Abstract In this paper we present experimental results for the optical dichroism of ultra-thin layers of an epitropic liquid crystal, 2,6-lutidine, on a carbonized quartz substrate. The carbon layer consists of carbon chains with an orientation perpendicular to the substrate surface. It significantly enhances the orientational order of the lutidine layers adjacent to the surface. A two-fold increase of the orientational order parameter S for 2,6-lutidine (from 0.22 to 0.45) has been measured due to the influence of the carbon layer. The inclusion of nitrogen atoms (nN = 7%) into the carbon film leads to a further increase of S from 0.45 to 0.65.