Molecular Dynamics Simulations on the Effect of Quenching Temperature on the Dielectric Energy Storage Characteristics of Polythiourea
In order to improve the energy density of polythiourea(PTU),the PTU was treated by quenching.The effect of hydrogen-bonding(H-bonding)kinetic properties on dielectric energy storage characteristics of PTU was studied by mo-lecular dynamics simulation.Firstly,the evolution of H-bonding pattern and strength with the increase of quenching temperature was described by means of thermal fluctuation index(TFI)and reduction gradient density(RDG).Secondly,the radial distribution function and autocorrelation function of H-bonds were calculated,and H-bonding density and av-erage lifetime were then extracted.Finally,the correlation between H-bonding characteristic parameters and dielectric constant was established.Based on the results above,the mechanism of quenching to improve energy density of PTU was revealed.The results show that,with the increase of the quenching temperature,the H-bonding pattern changes from di-hydrogen bonds to single H-bonds,and eventually exceeds the H-bonding threshold,which is difficult to form H-bonds.It is accompanied by decreases in the H-bonding density,resulting in decreases in strongly polar dihydrogen bonding thiou-rea arrays and thus the dielectric constant.Meanwhile,the H-bonding strength gradually weakens as the quenching temperature increases.Moreover,the H-bonding lifetime is shortened and the dynamic motions is accelerated,which is conductive to reducing the barrier for the orientation of thiourea arrays and increasing the dielectric constant.Owing to the changes of H-bonding patterns and strength,the dielectric constant increases first and then decreases with the increas-ing quenching temperature.When the quenching temperature is 393 K,the dielectric constant of PTU increases to 10 and the energy density reaches 16.3 J/cm3.
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