Regulation of Hydrogen Bonding Interactions for Improving Dielectric Energy Storage Characteristics of Polythioureas
To understand the mechanism of H-bonding interactions on dielectric energy storage characteristics of polythiourea(PTU),the effects of H-bonding patterns and strength on dielectric constant,breakdown strength and energy density are investigated for the alicyclic PTU(AcPTU)and aromatic PTU(ArPTU)based on experiments and molecular simulations.Their chemical compositions and conformations are characterized by infrared and nuclear magnetic resonance spectra.The dielectric energy storage characteristics are obtained from broadband dielectric spectra,breakdown strength and D-E hysteresis loops.The dielectric relaxation strength of the dipole polarization is extracted based on the H-N formula and the trap depth is achieved by thermal stimulus decurrent method.The H-bonding patterns and strength are identified and analyzed by the Multiwfn software.The experimental and simulation results show that the H-bonding patterns and strength affect the dielectric properties by changing the dipole polarization and trap characteristics.The alicyclic structure increases the dihydrogen-bonding arrays that are assembled from trans/trans conformational thioureas.The dihydrogen-bonding arrays enhance the dielectric relaxation strength and thus increase the dielectric constant.The benzenes enhance the number and intensity of π H-bonds.It deepens the trap level contributed by H-bonding acceptors,including carbon atoms of benzenes and sulfur atoms,thereby improving the breakdown strength.AcPTU has a high dielectric constant due to the enhanced dielectric relaxation strength of the dihydrogen-bonding array.ArPTU exhibits high breakdown strength up to 855 MV/m because the benzene structure enhances the H-bonding effect on hindering charge transport.Additionally,when the electric field of 300 MV/m is applied,the energy density and efficiency of AcPTU reach 2.62 J/cm3 and 93.31%,respectively.This study provides a theoretical basis for improving the dielectric energy storage characteristics of intrinsic polymers.
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