Experimental investigation of tribological properties of cholesteric liquid crystals as oil additives

Abstract

The tribological behaviour of cholesteric (twisted nematic) liquid crystals (fatty acid cholesteryl esters-cholesteryl valerate and stearate) as commercial mineral motor oil additives was investigated using a block-on-disc tribometer at constant sliding velocity and variable load, concentration in oil and average depth of roughness of steel-steel friction surfaces. The average friction coefficients of friction pair lubricated with oil with and without additives and near contact temperature after the test measured at 0.8 mm depth from the contact point were served as output parameters. Regression equations describing the relationship between output parameters and factors were obtained for each lubricant and tribological performance of liquid crystalline additives then was evaluated. It is established that friction coefficient of steel-steel friction pair and friction zone temperature are significantly reduced by addition of liquid crystals. Results show that tribological efficiency is increased with increase of molecular weight of the liquid crystalline additive.