Effect of H-Bonding Interaction on Breakdown Strength of Polythiourea

The construction of a new power system requires the support of dielectric film capacitors. As the breakdown strength is crucial for the development of dielectric film capacitors, H-bonded polythiourea (PTU) capable of withstanding high electric fields presents itself as a potential working material for capacitors. However, since the effect of H-bonding interaction on the breakdown strength of PTU remains unclear, a combination of molecular dynamics simulation and experiments is employed to investigate the dependence of breakdown strength on the H-bonds. The results of molecular dynamics simulations demonstrate that the H-bonding patterns and strength in PTU can be effectively tailored by adjusting the quenching temperature, leading to differences in fractional free volume. The weakened H-bonding interaction resulting from enlarged H-bonded trans/trans conformational thiourea arrays leads to an increase in the fractional free volume. This value abruptly increases from 4.94% for the pristine PTU to 5.62% as the quenching temperature approaches 403 K. Experimental results indicate a high correlation between the breakdown strength and the quenching temperature. With increasing quenching temperature, the breakdown strength gradually decreases. Specifically, when the quenching temperature reaches 403 K, there is a sharp decrease from 652 MV/m for the pristine PTU to 585 MV/m for the quenched PTU. The combination of simulation and experimental results suggests that the breakdown strength of PTU is strongly associated with the H-bonding strength. The fractional free volume, dominated by H-bonds, determines the breakdown strength. A stronger H-bonding interaction results in a smaller fractional free volume and a larger breakdown strength. These findings provide insight into the correlation between H-bonds and breakdown strength.