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 50 N and smectic B mixtures have low friction coefficient under 20 N, 30 N and 40 N load.

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ABSTRACT:The effect of the chemical structure and stereogeometry of mesogen on the liquid crystalline properties of thermotropic main-chain polyesters was studied by means of DSC and polarized microscopy for three series of polymers. The polyesters obtained from modified 4,4'-dihydroxybenzophenone (DHBP) and sebacoyl (SEB) or suberoyl (SUB) dichlorides did not exhibit the mesogenic properties. Modification of DHBP in this case consisted in replacement of ketone linkage by between two aromatic rings. The same bisphenol, however, when mixed with CC12 another (showing meso genic behaviour) enhanced the liquid crystalline properties of the copolyesters, namely increasing the temperature range of liquid crystalline phase. The condensation of SEB or SUB with DHBP modified by lateral substitution (at various positions) of one aromatic ring with CH3 group lead to polyesters of lower temperatures of the transition from crystal to nematic phase and mesophase to isotropic liquid, as compared to parent polymers (i.e., polyesters ofDHBP+SEB or SUB). Different shifts of those temperatures with the position of substitution have been observed and it was found less pronounced for 3-substituted than 2-substituted bisphenols. Temperature ranges of mesophases also depended on the structure of bisphenols and were broader for 3-substituted DHBP. Therefore, the stereogeometry of the polymer molecules and the bulkiness of their substituents are considered the most important parameters in controlling the mesogenic properties of thermotropic, rigid-flexible polyesters with mesogens incorporated in the main chain.

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 influence of the polar compound added to the binary mixture with the phase transitions Nre4nduced Ad-N was tested by thermomicroscopy. The enhancement or the destabilization of the induced smectic A phase was observed after adding 1OTPCHB, 6TPCHB, 1OCPCHB, 6CPCHB, 1O.CN and 1O.NCS. It corelates with the behavior of these compounds in binaiy mixtures with 7BCB.