Preparation and Dielectric Properties of Cross-linked Poly(Aryl Ether Sulfone) Nanocomposites

Author:Liu Jie

Supervisor:zhang yun he


Degree Year:2019





Dielectric capacitor can release stored electrical energy in a fraction of a second(millisecond),resulting in producing a burst of energy,which is not available in other power storage devices such as batteries and super-capacitors.This feature makes it widely used in pulsed power systems,power electronic converters,new energy vehicles,power grid frequency modulation and other fields requiring high power density.As the core material of capacitors,high-performance dielectric materials still have the problem of low energy storage density(the ability to store charge).If the energy storage density can be increased by 2-3 orders of magnitude,it will bring a major breakthrough to related electronics,energy and other technical fields.High power density,high voltage capacitor,power storage device miniaturization,miniaturization and lightweight stimulate the rapid development of polymer dielectric materials,but to polymer dielectric materials(including polymer dielectric composite materials)as the main body of the capacitor is still poor thermal stability,not of the work under the environment of high temperature stability,especially under the effect of high electric field,the temperature can cause the polymer dielectric internal leakage current exponential rise,causing a sharp drop in charging and discharging efficiency and energy storage density.The study of polymer dielectric materials with high temperature resistance and high energy storage density,especially those with high energy storage density and charging and discharging efficiency at high temperature(≥150 o C)is still facing challenges.In this thesis,by designing and synthesizing cross-linked poly(aryl ether sulfone)(DPAES)and reactive functional groups modified on the surface of inorganic barium titanate nanoparticles(BT),different forms of cross-linked network structure can be constructed.The effects of different cross-linking methods and different nanometer cross-linking points on the performance of high temperature dielectric energy storage of composite materials were systematically studied,and the relationship between interface structure and properties of composite materials was analyzed by means of phase field simulation and finite element simulation.The main research contents are as follows:1.We designed and synthesized a self-cross-linking poly(aryl ether sulfone)containing pendant propylene groups with a high glass transition temperature.Through high temperature thermal cross-linking,we prepared a series of cross-linked poly(aryl ether sulfone)/Ba Ti O3 composites(BT/c-DPAES).Compared with not cross-linked composites(BT/DPAES),BT/c-DPAES showed better mechanical properties and thermal properties,eg: 10 vol% BT/c-DPAES has a Young’s modulus of 2.7 GPa,tensile strength of 70.3 MPa,elongation at break is also above 4.2%,glass transition temperature is as high as 234 oC,which makes it have good high temperature dielectric stability and energy storage performance.In particular,at 150 oC and 200 MV m-1,BT/c-DPAES has better energy density and charge-discharge efficiency than BT/DPAES,indicating that the molecular chain restriction via the polymer cross-linking network can effectively improve the dielectric energy storage performance of the composite at high temperatures.2.In order to further expand the construction method of cross-linking network and improve the high-temperature dielectric energy storage performance of polymer composites,we proposed for the first time the construction strategy of "double cross-linking network structure",that is,the cross-linking network between nanoparticles and polymer and the cross-linking network of polymer itself co-exist.With the difference in activation energy of different functional groups of BT-BCB and DPAES,controllable preparation of double cross-linked network structure BT-BCB@DPAES(D)was realized by controlling the cross-linking temperature and time.When the content of BT-BCB is 10 vol%,the energy storage density of BT-BCB@DPAES(D)under 400 MV m-1 is 3.1 J cm-3,and the charging and discharging efficiency remains above 75%.3.In order to explore the influence of interface cross-linking network on dielectric properties,a phase field model was developed to study the breakdown process of composite materials with different cross-linking modes from the perspective of local electric field and energy density.Through phase field simulation,we found that the cross-linking network between the interface and the polymer makes the electrical conductivity at the interface similar to that of the polymer,with high insulation,and is conducive to alleviating local electric field distortion,reducing leakage current and reducing joule heat at the interface.Moreover,the breakdown evolution path simulated by the phase field shows that the construction of composite materials BT-BCB@DPAES(D)with double-cross-linked network structure can effectively prevent the breakdown from happening compared with single cross-linked network.This structure makes it have a high characteristic breakdown strength of 442 MV m-1 at 150 oC.And then,the composites possess long-time cycle stability at 150 oC and 200 MV m-1.The above analysis shows that the strategy for constructing double cross-linked network has excellent superiority in improving high temperature energy storage density and charge and discharge efficiency.4.To improve dielectric mismatches and reduce interface defects in polymer/ceramic composites by introducing nanoparticles of different sizes to regulate the size of cross-linking degree.The effects of cross-linking degree on thermal properties,mechanical properties,dielectric properties and energy storage properties of composite materials were studied systematically.The more uniform distribution of the local electric field in the 100 nm BT-BCB@DPAES nanocomposite results in enhanced breakdown strength,which is consistent with the characteristic breakdown strength of the experimental data.The results show that the proper cross-linking degree plays a positive role in improving the breakdown strength even though the interfacial polarization can cause the deterioration of the breakdown strength at high temperatures,affecting the dielectric energy storage performance of the composite materials.In summary,the composites with double cross-linked network structure possess excellent dielectric stability at 20~200 oC,and have high energy storage density,high charge-discharge efficiency and long cycle performance at 150 oC,which have a potential application prospect in the development of capacitors with high temperature resistance and high energy storage density.