Study On The Thermal Behavior For Carbon Nanotubes/Rubber Composites With The Action Of Magnetic Field

The rubber is widely used in daily life and industrial production due to its excellent physical and chemical properties, but the low thermal conductivity limits its use in the field where the good thermal performance is needed. There is incomparable potential in taking multi-walled carbon nanotubes (MWNTs) as the thermal conductive filler for improving the thermal conductivity of rubber due to their extremely high thermal conductivity. The effect of external magnetic field can prompt the MWNTs to orient in rubber matrix and make full use of the axial performance advantages of MWNTs, which is conducive to further improvement of the thermal performance of rubber composites. However, the research on thermal property of carbon nanotubes/rubber is less or the result is negative at present due to the high flexible, low modulus, big adhesive capacity and machining difficulty of rubber matrix. Therefore, the thermal behavior for carbon nanotubes/rubber composites with the action of magnetic field was investigated by the numerical and experimental methods.In the part of numerical calculations, it included two works.The lattice Boltzmann method (LBM) is suitable for dealing with complex geometry boundary conditions and multiple interparticle interactions, and the program implementation is simple. Therefore, the LBM has been used to study the thermal performance of the composite material. Firstly, the MWNTs/rubber composites microstructure models with different MWNTs orientations are reproduced by using computer and then a 3-D lattice Boltzmann method is proposed to compute the effective thermal conductivity of the composites. The effects of the orientation, volume fraction and diameter of MWNTs on the effective thermal conductivity of composites are quantified using this model. It is found that the thermal conductivities of the composites decrease with the increase of the angle between the axial direction of MWNTs and the direction of heat flux in matrix, and the decrease extent deduces gradually. The thermal conductivities of rubber composites have been improved remarkably when the MWNTs orientation is parallel to the direction of heat flux. Moreover, the difference between thermal conductivities of MWNTs/rubber composites with different MWNTs orientations increases when increasing the volume fraction of MWNTs. The thermal conductivity of the composites filled with small diameter MWNTs were larger over a certain range of volume fraction of MWNTs.The interfacial resistance plays an important effect to the thermal properties of carbon nanotube composites, but the LBM calculation model based on interface temperature continuity condition, which is difficult to give the influence of interfacial resistance on the MWNTs/rubber composites at present. ANSYS can be easily to study the effect of interfacial resistance on the rubber composites by setting thermal contact conductance. In order to further study the thermal performance of MWNTs/rubber composites, a representative volume element model of aligned MWNTs/rubber composite was developed based on continuum medium theory, and then the effective thermal conductivity of the composites is computed by using the finite element method. The effect of the interfacial thermal resistance on the effective thermal conductivity of composites is studied using this model. The results show that the interfacial resistance hinders the heat transfer between MWNTs and matrix and it has a great influence on the thermal conductivity of composites. Moreover, with the different volume fractions of MWNTs, the thermal conductivity of rubber composites decrease when increasing the interfacial resistance at the first time, but it will remain basically unchanged when the interfacial resistance increases to a certain value.Numerical calculations show that MWNTs orientation has a great influence on thermal conductivity of the composites. Therefore, in the experimental part, in order to make MWNTs orient well in rubber matrix, MWNTs will be magnetic modified firstly and Cooperation Precipitation was utilized to deposit Iron oxide (Fe3O4) on the surface of MWNTs; Then, Fe3O4/MWNTs magnetic nanoparticles were prepared; Finally, we obtained MWNTs/rubber composites with different MWNTs orientations by solution blending method with the action of the magnetic field. The effects of Fe3O4 magnetic particles, the intensity and the direction of magnetic field on the thermal conductivity .of rubber composites were studied through experimental test. The main conclusions are as follows:The MWNTs coated with Fe3O4 magnetic particles have good magnetic field response, but larger interfacial resistance exists between Fe3O4/MWNTs and rubber matrix due to their poor interfacial adhesion. The orientation degree of MWNTs is improved by increasing the intensity of magnetic field and the thermal conductivity along the direction of heat flux of rubber composites increased, but this growth trend will flatten out within the fields in excess of 430 mT. The smaller the angle between the MWNTs orientation and the direction of heat flux, the bigger the thermal conductivity along the direction of heat flux of rubber composites. Compared with the numerical calculation results, we can find that the variation trend of the thermal conductivity of rubber composites with increasing the MWNTs orientation is almost the same. However, due to the larger interfacial resistance and the limit of preparatory technological conditions, the experimental results are much lower than the results of theory analysis.