Measuring the temperature dependent thermal conductivity of multiwall carbon nanotubes based nanolubricants by 3 omega method

The main purpose of this study is to utilize the well-known three-omega method for accurately measuring and inspecting the thermal conductivity of multiwall carbon nanotubes nanolubricants under the influence of temperature. For that, pure multiwall carbon nanotubes, without any special treatment, were dispersed in six types of oils at three different weight concentrations (0.05, 0.1 and 0.3 percent by weight) by ultrasonication and without using any stabilization method. First, the study focused the light for the first time on the recognized re-dispersion ability of the sonicated multiwall carbon nanotubes within oil. After full agglomeration, it was realized that agitating, shaking or even blowing compressed air on the agglomerated nanolubricant is able to break down the aggregation of the tubes. Quantitatively, viscosity, thermal conductivity and particle size distribution measurements were employed to evaluate the re-dispersion quality. It was observed that the sonicated tubes are separated, saturated, lubricated, and surrounded by oil layers, which not only ease its motion within the lubrication oil, but also counter balanced the Van der Waals forces which give them the ability of detaching by applying any slight force. Microscopic video is presented to clarify the behavior of the tubes during the re-dispersion process. Second, Thermal conductivity measurements were then performed with respect to temperature. The high sensitivity of the three-omega lab-made setup allowed to observe that the thermal conductivities of the nanolubricants peak at specific temperatures and then decay to the value of the base oil. Moreover, microscope images revealed that heating the nanolubricants to higher temperatures (60 to 80 degrees Celsius) resulted in agglomeration of the tubes due to the disappearance of the oil separation layers. Moreover, convection currents act as agitator which also increases the contacts between the multiwall carbon nanotubes.