Molecular simulation of the effect of plasma modification on the microscopic properties of polyimide

Abstract

Polyimide is often used as the insulating material of the repulsion coil, which needs to withstand the collision of the fast repulsion mechanism in high-speed motion and temperature rise. The polyimide molecular model was established in this study. The external electric field was applied to the model through the semi-empirical method to calculate the total molecular energy, dipole moment, molecular orbital energy, and energy gap of polyimide. It was found that the total molecular energy of plasma-modified polyimide was lower, the energy gap was smaller, and the corresponding molecular properties were more stable. Then, the cell models of ordinary polyimide and plasma-modified polyimide were established by molecular dynamics simulation. The effects of plasma modification on the micro properties of polyimide were studied and compared. The free volume, mean square displacement, cohesive energy density, mechanical properties, and relative dielectric constant of polyimide models with different modified ratios were calculated. The results show that the introduction of polar groups through plasma modification can inhibit the movement of the polyimide molecular chain and improve the thermal stability of the polyimide system. The mechanical properties of polyimide are also improved due to plasma modification, and the elastic modulus is the largest when the modification rate is 20%. At the same time, the relative dielectric constant of polyimide increases with the increase of the modification rate.

Atomic Insight into Multilevel Microstructure Evolution and Energy Variation Mechanisms of Polyimide under Shock Compression

“…Figure displays the density and energy curves during the PI model preparation, indicating that the system tends toward equilibrium and an energy-minimum state. The final density of the PI model is approximately 1.355 g/cm 3 , which aligns with MD results ranging from 1.33 to 1.36 g/cm 3 reported in the refs ,, and is also close to the actual experimental density of PI material (ranging from 1.35 to 1.42 g/cm 3 ,, ).…”

Polyimide (PI) Composite Spunlace Nonwovens for Hygiene Material with Excellent Comfort and Antimicrobial Properties

“…Polar groups can affect the charge balance inside and outside the bacterial cell, thereby disrupting the cell barrier and leading to cell inactivation. It is believed that a grafting reaction on the fiber surface caused by the plasma induces the significant decrease in the number of -C-C-/-C=C-groups [37]. This reaction is oxidized to produce oxygen-containing groups including -C-O-and -O-C=O, which is compatible with an immense rise in the content of -C-O-and -O-C=O groups after treatment.…”

Preparation and Properties of Low-Dielectric Polyimide Films Containing Tert-Butyl

“…The diamine segment of tert-butyl PI is a non-planar tert-butyl structure where the tert-butyl group twists at a certain angle. Such a non-planar conjugated structure in the main chain can hinder the close packing of the polymer chains and segments, which contributes toward increasing the local free volume and reducing the dielectric constant [31][32][33][34]. In addition, the introduction of functional groups (e.g., C=O, -O-, and benzene ring) in anhydride can greatly reduce the molecular polarizability and decrease the packing density, thus resulting in a decrease in the dielectric constant of tert-butyl PI films.…”