Preparation And Study On Thermal Conductivity Of 2D Nanosheets And Their Composites

Thermal conductive polymer composites can be widely used in many fields such as energy and electronics.The 2D nanosheet is a kind of heat-conductive filler with excellent properties.The composites filled with nanosheets is the hotspot of current research.In this paper,experimental preparation and theoretical analysis of 2D nanosheets such as Ti3C2Tx,h-BN(where Tx refers to a variety of functional groups on the surface)and their composites were carried out.The thermal conductivity and other properties of 2D fillers and their composites were discussed.Firstly,a new 2D MXene material was studied with Ti3C2Tx.The Ti3C2Tx films were prepared by a series of experiments,tested by the T-shaped method and characterized by scanning electron microscopy.The results show that within the testing temperature range between 80 K and 290 K,the electrical conductivity of the Ti3C2Tx films remains almost constant at?12500?-1m-1.In comparison,the effective thermal conductivity of the same films increases from 1.3 Wm-1K-1 at 80 K to 3.05 Wm-1K-1 at 290 K,which is mainly attributed to the combined effect of heat capacity and phonon mean free paths variations ofTi3C2Tx flakes.By applying the unit cell model,the inherent thermal conductivity of Ti3C2Tx flakes is estimated to be in the range of tens to hundreds Wm-1K-1 and the thermal resistance between Ti3C2Tx flakes is less than 3×10-6 W-1m2K.Secondly,the h-BN/PP composites were prepared,its properties test and characterization analysis were carried out.The effects of h-BN content,particle size and processing method on the TC of composites were studied.The experimental results showed that the in-plane and through-plane TC of the h-BN/PP composites were improved with the increasing of h-BN mass fraction,but no more percolation occurred at the maximum filling of 22wt%.The in-plane and through-plane TC of the composites filled with 5-10?m BN are better than the composites filled with 30?mBN,which is mainly because the effective TC of the composites combines the contact thermal resistance and the TC of h-BN.Both hot-pressing and injection molding can make h-BN has a certain orientation in the matrix PP,resulting in a difference between the in-plane and through-plane TC,but the injection molding enables a better orientation of h-BN in PP(the averaging orientation is closer to in-plane)so that its in-plane TC is higher.Finally,based on the existing composites TC calculation model,the TC model of the composites filled with 2D nanosheets and particles is established by the method of thermal resistance series-parallel connection.Six kinds of typical filler distributions are proposed and their in-plane and through-plane TC are calculated.The results of analysis and calculation show that,in a certain direction,the less the "coplanar" fillers in the cross-section perpendicular to the direction,the smaller the thermal resistance in this direction,the larger the TC.According to the analysis and calculation results,a hybrid filling optimization distribution is concluded.