Study On The Dielectric Properties Of Polystyrene Enhanced By Modified Mutil-walled Carbon Nanotubes

With the ultra-high speed development of electronic industry and information technology,traditional capacitor materials is facing enormous challenges.The dielectric nanocomposites,with high dielectric constant and low dielectric loss,have attracted wide attention in the field of microelectronics,such as,integrated electrically induced contraction film capacitor,artificial muscle systems and electric stress control devices,etc.Generally,the main method to increase the dielectric constant is to introduce nanometer ceramic fillers or conductive fillers with high dielectric constant into the polymer matrix to prepare the nanocomposites.Although these fillers had a high permittivity,the dielectric loss of the nanocomposites increases greatly and the breakdown strength decreases obviously due to its easy agglomeration,when they were introduced into the matrix material.Therefore,the preparation of nanocomposites with high dielectric constant and low dielectric loss is of great significance.In this study,the multi-walled carbon nanotubes(MWCNTs)/polymer nanocomposites based on carbon nanotubes(MWCNTs)as the main filler,and the polymer matrix had low to dielectric loss of polystyrene(PS).MWCNTS/polystyrene nanocomposites were prepared by grafting an insulating layer on the surface of fillers through different modification methods to reduce dielectric loss.The specific contents of the experiment are as follows:(1)MWCNT was made to carry thiol groups with chain transfer properties on the surface by a simple modification.In the process of radical polymerization,the unreacted polystyrene chain segments were transferred to the surface of MWCNT to form a layer of polystyrene shell structure.The dielectric properties of the composites were studied with different filler contents.According to transmission electron microscopy,thermogravimetric analysis and nuclear magnetic resonance analysis,the graft of polystyrene shell on MWCNT was successfully obtained.According to the thermal stability analysis,with the increase of MWCNT content,the thermal stability of composites is higher.The higher dielectric constant of the composites was 214(100 Hz),and the lower volume fraction(4 wt%)had a dielectric loss of 2.23(100 Hz),indicating that this modification method is an effective way to improve the dielectric properties of the nanocomposites.(2)MWCNT fillers of different shell thickness were prepared in different monomer proportions through the homemade RAFT reagent in the laboratory and the advantage of controllable polymerization of RAFT reagent.The results of nuclear magnetism,thermogravimetric analysis and transmission electron microscopy show that the MWCNT successfully coated polystyrene has a shell layer,and the thickness of the shell layer is obviously different according to the ratio of monomer addition.When different kinds of fillers are introduced into the polymer matrix,various kinds of composites exhibit different dielectric behaviors.When the content of three different fillers reached 0.6%,the dielectric constant of MWCNT-OH/PS composites reached 11.5,and the dielectric loss was also very high,around 0.085.While the value of the dielectric loss of the modified composite decreased by about half from 0.085 to 0.01,which decreased by 7 times.By comparing the modified composites,it is not difficult to see that the thicker the polymer shell is,the greater the dielectric loss inhibition is,and the higher the dielectric constant is.This shows that we have achieved the goal of changing the thickness of the polymer shell to regulate the dielectric properties of the composites,and have a significant effect on the improvement of polarity and frequency dependence.