Tailoring The Dielectric Property Of PVDF Film Via Using Semiconductive Side-chain Triphenylene Discotic Liquid Crystalline Polymers

Polymer dielectric materials have a good development prospect in modern power supply and renewable energy systems because of their easy processability,very good flexibility and excellent electrical properties.However,the dielectric constant(ε)of most polymers is very low(<10),which increases the volume of materials in the field of dielectric energy storage.Therefore,how to improve the dielectric constant of polymer materials has become a problem.At present,there are two main methods to prepare high dielectric constant polymer materials.One is polymer alloy materials prepared by polymer blending,maintaining the flexibility of the polymer,well processability and light weight.But there are some problems to affect the properties of polymer blends,including the function of adding polymers and the compatibility between different kinds of polymers.The other is polymer-based nanocomposites,which theoretically can combine the advantages of polymer matrix and ceramic nanoparticles and produce the high dielectric costant,low loss and high energy storage.However,the interfacial problem and the poor dispersion of ceramic nanoparticles and compatibility between polymer matrix and ceramic nanoparticles lead to reduce the dielectric energy storage properties of the composites.Semiconductor side-chain triphenylene discotic liquid crystalline polymer(PHT)has the characteristics of high electron mobility,self-assembly order,good solubility,processability,controllable molecular weight,easy synthesis and so on.These properties are very beneficial to the blending of polymers and the surface modification of inorganic ceramic nanoparticles.Therefore,aiming at the existing problems in polymer blends and ceramic/polymer dielectric composites,the following studies have been done in this paper:(1)Three p-type semiconductor triphenylene discotic side chain liquid crystalline polymers,homopolymer(PHT),copolymer(PHT-co-P9F)and block polymer(PHT-b-P9F),were synthesized by traditional free radical polymerization and reversible addition fragmentation chain transfer method,in which PHT is poly{2-[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]methacrylate}and P9F is poly[2-(perfluorobutyl)ethyl methacrylate].Polymer alloy films were prepared by blending three kinds of polymers with polyvinylidene fluoride solution respectively.The compatibility and dielectric properties of a series of polymer alloys were studied.The results show that the dielectric properties of polymer alloys are related to the ordering of PHT and the compatibility between PHT and PVDF.Among the three kinds of polymer blends,the compatibility between PHT-b-P9F and PVDF is the best,because the F-H bond is formed between P9F and PVDF,which greatly improves the dielectric properties of PHT-b-P9F/PVDF polymer alloys.The maximum dielectric constant of 50 wt%PHT-b-P9F/PVDF at 100 Hz is 35.5,which is 4.23 times higher than that of pure PVDF.(2)The PHT is covered to the surface of barium titanate nanoparticles(BT)to enhance the dispersibility of BT nanoparticles and the compatibility between BT and polymer matrix and improve the interfacial polarization via utilizing the conductive property and steric hindrance effect of PHT.BT@PHT nanoparticles with core-shell structure were successfully prepared by RAFT method,and the corresponding BT@PHT/PVDF composites were fabricated by solution blending.The dielectric energy storage properties of the composites were characterized in detail by dielectric spectroscopy.The results showed that the maximum dielectric constant of 50 wt%BT@PHT/PVDF composites can reach 22.0 at 100 Hz.Compared with PVDF matrix,the dielectric loss and conductivity of all composites have no obvious change.In addition,the maximum energy storage density of 0.2 J/cm~3 was achieved in the 40 wt%BT@PHT/PVDF composites under 50 KV/mm electric field.This work provides a new idea for the realization of new dielectric materials with high dielectric constant,low dielectric loss and high energy storage density,and also reveals the effect of interface polarization on the dielectric behavior of dielectric materials.