B. Ważyńska’s research while affiliated with AGH University of Krakow and other places

The mixtures of two liquid crystalline compounds (6CHBT and 6CB) with paraffin oil of different concentration were tested as lubricating agents. A great decrease of friction coefficient was observed after doping the paraffin oil with liquid crystalline compounds, specially for higher loads (40, 50 N). The compound with cyano group 6CN gives better improvement of lubricating properties. The FT-IR measurements of tested mixtures shown the tendency of liquid crystalline molecules to accumulate on the metal surface.

Few liquid crystalline compounds and mixtures were tested as lubricating agents. The much decrease of friction coefficient was observed in comparison to the paraffin oil, the commonly used reference lubricant. The compounds were differing in chemical structure as well as the kind of formed liquid crystalline phases. The chemical structure plays a crucial role in the improvement of tribological properties.

The paper presents description and analysis of the results obtained in the investigation performed on a disc-ball tribotester T-11. Samples of 100Cr6 steel were tested, while as lubricant the mixtures of paraffin oil, with addition of 0.5%, 1%, and 2% of liquid crystalline compounds, from two homologous series defined with nOBCAB and nCBB symbols, were used. The friction force and wear of a sample and a counter-sample were measured. The improvement in tribological and anti-wear properties was found for all mixtures in relation to paraffin oil. The best tribological properties and the best wearability were obtained for mixtures with a compound 8CBB. This compound differs from the others in formation of different liquid crystalline phases.

The paper presents the description and analysis of the results obtained in the investigation performed on disc—ball tribotester T-11. Samples of 100Cr6 (European) steel were tested, while as a lubricant, liquid crystalline mixtures in nematic as well as smectic A, B and E phases were used. The friction force and the wear of sample and counter-sample were measured. The analysis of values of friction coefficients has shown that the friction coefficient of liquid crystalline mixtures is lower than that of paraffin oil. Nematic mixtures have a low friction coefficient under a load of 50N and smectic B mixtures have low friction coefficient under 20N, 30N and 40N load.

In the mixture of two nonpolar compounds with the destabilization of smectic A phase the selective reflection of the light is from red to blue with increasing temperature and in the mixture of two polar compounds with the induction of smectic Ad phase the selective reflection of the light is from blue to red with increasing temperature. To check if the polarity of compounds are responsible for the differens in colour changes of the selectively reflected light two nonpolar, two polar, and polar and nonpolar compounds were mix together. It was found that the polarity of compounds do not influence the colour sequence only the distance of the compositions giving selective reflection of the light in the temperature-concentration scale from smectic phase.

AFM studies of mixtures with different smectic A, B and E phase were done. Compounds with terminal NCS group were used. AFM images were obtained for liquid crystals samples spread on mica surface or mica covered by polyvinyl alcohol in order to examine the influence of molecular orientation.

The influence of the polar compound added to the binary mixture with the phase transitions Nre-induced Ad-N was tested by thermomicroscopy. The enhancement or the destabilization of the induced smectic Ad phase was observed after adding 10TPCHB, 6TPCHB, 10CPCHB, 6CPCHB, 10.CN and 10.NCS. It correlates with the behavior of these compounds in binary mixtures with 7BCB.