DFT and molecular dynamic simulation for the dielectric property analysis of polyimides

Electron displacement polarization of high-dielectric constant fiber separators enhances interface stability

The electrostatic effects of separators under the internal electric field are often overlooked, leading to the unreliability of traditional theoretical models. Here we introduce the dielectric constant as a descriptor and develop a high dielectric constant fiber separator primarily composed of phosphorylated cellulose. Under the internal electric field, the intense electron displacement polarization within the high dielectric constant separator enhances the charge transfer kinetics and optimizes the solvation structure, thus mitigating the formation of amorphous organic oligomers at the solid-electrolyte interphase. Furthermore, the separator induces the formation of LiF, thereby forming a robust and low-resistance solid-electrolyte interphase. The separator exhibits high ionic conductivity (0.76 mS cm-1 at 25 °C) and Li+ transference number (0.68). Consequently, the Li||LiFePO4 pouch cell with the prepared separator achieve high specific energy exceeding 350 Wh kg-1 (relative to the mass of pouch cells) under practical quantities of active materials and electrolyte.

Influence mechanism of vacancy defect effects on the intrinsic electronic properties of h-BN and the thermodynamic and dielectric properties of h-BN/PI interfaces

Polyimide (PI), known for its excellent properties, has been widely applied across various fields. However, its thermodynamic and dielectric properties require further enhancement. Hexagonal boron nitride (h-BN) is commonly employed as a nano-modifier to enhance the properties of the PI matrix. However, the vacancy defects in h-BN limit the improvement of the composite's properties. In this study, molecular simulation techniques are utilised to investigate the effects of vacancy defects on the electronic properties of h-BN and the interfacial properties of h-BN/PI composites. The simulation results indicate that as the number of vacancy defects increases, the distortion of the h-BN geometric structure becomes more severe. Among the single-atom vacancy defects, N-atom vacancies exert a more significant impact on the geometrical structure and insulating properties of h-BN. Two defect levels are introduced into the energy band structure of the diatomic vacancy defect model, thereby weakening the insulating performance of h-BN. The band structure of the three-atom vacancy defect model undergoes greater changes, with additional defect levels introduced into the band gap, resulting in reduced insulating performance and a semi-metallic state in h-BN. As the number of vacancy defects increases, the thermal conductivity and mechanical properties of the h-BN/PI interface deteriorate. In contrast, B-atom vacancies have a more pronounced effect on interfacial heat transfer, whereas N-atom vacancies more significantly affect mechanical properties. The free volume fraction of the model increases as the vacancy defect rate rises, leading to an increase in the relative dielectric constant of the h-BN/PI interface. This paper comprehensively examines the effects of vacancy defects on the interfacial properties of h-BN/PI composites, providing a foundation for the application of h-BN as a filler in the functional modification of PI.

Green Synthesis of Vat Photopolymerization 3D Printing Polyimide

Vat photopolymerization (VP) 3D printing polyimide (PI) has the combined advantages of 3D printing in free-form manufacturing and PI in comprehensive properties. While, the inks for VP 3D printing PI are generally involve in complicated synthesis process of photosensitive oligomers or precursors, which undoubtedly result in serious environmental issues because of significant amounts of solvents and wastewater during the precipitation and purification. Here, a VP 3D printing PI is designed via a novel one-pot environmentally-friendly approach with reactive dilute N-vinyl pyrrolidinone (NVP) as the solvent. NVP, similar to the conventional solvent N-methyl pyrrolidinone (NMP) used for PI synthesis, serves as the solvent during synthesizing the precursor double-bonds containing amide-acid while functions as the reactive diluent directly in the final photosensitive ink, thereafter, generating not even a drop of waste solvent or water because needless of precipitation of oligomers as usual. The resultant inks show good printability and low shrinkage of 11%, resulting in architectures with precision and complex structures, excellent thermal and mechanical performance of glass transition temperature (233.1 °C) and tensile strength (58.1 MPa), respectively. The method paves the green way for developing PI 3D architectures and functional devices, demonstrating significant potential in aerospace, microelectronics, and many others.

Si, B-containing dynamic covalent bonds enable excellent flame retardancy and reduced fire hazards for cyanate ester resin

Cyanate ester (CE) resins are distinguished by excellent dielectric properties in electronic packaging materials but face significant fire risks, with existing strategies often compromising their processability or original properties. Herein, we propose an innovative strategy involving the exchange of dynamic covalent bonds under heat stimuli aimed at forming a continuous and compact char layer to enhance the fire safety of CE resin. Using a straightforward one-pot method, dynamic Si-O and B-O bonds were integrated into a novel hyperbranched polymer (HPSiB), ensuring good compatibility with CE resin while lowering its peak curing temperature by 185 °C for facile processability. The resulting material with 6 wt% HPSiB exhibits a LOI value of 32.8% and UL-94 V0 rating, especially a low total smoke production of 6.7 m2, demonstrating excellent flame retardancy and reduced fire hazards compared to reported Si or B-containing flame-retardant materials. Moreover, its glass transition temperature increased by 35 °C, along with enhanced mechanical properties and an ultra-low dielectric loss of 0.0031 at 10 GHz. These advancements highlight the significant potential of this work in developing high-performance fire-resistant materials.

High comprehensive properties of colorless transparent polyimide films derived from fluorine-containing and ether-containing dianhydride

Fluorinated colorless transparent polyimide (CPI) films are crucial for flexible displays and wearable devices, but their development is limited by high costs and relatively low mechanical properties. In this study, a series of colorless transparent polyimide films was synthesized by incorporating the cost-effective ether-containing diamine, 4,4'-isopropylidenediphenoxy bis(phthalic anhydride) (BPADA), into commercially available 4,4'-(hexafluoroisopropyl)diphthalic anhydride (6FDA) and 2,2'-bis(trifluoromethyl)benzidine (TFMB). The comprehensive properties of the films were systematically investigated using a combination of experimental and numerical methods, including molecular dynamics (MD) simulations and density functional theory (DFT). This study focuses on exploring the influence of varying dianhydride ratios on the aforementioned properties. The incorporation of BPADA in the dianhydride significantly enhances the mechanical properties and flexibility of the film. When the ratio of ether anhydride to fluorine anhydride is 4 : 6 (CPI-4), the tensile strength is 135.3 MPa, and the elongation at break is 8.3%, which is 109.6% and 118.45% higher than that of the original film without ether anhydride. This research provides valuable insights for the future application of new polyimide materials in flexible display devices.

Data science-centric design, discovery, and evaluation of novel synthetically accessible polyimides with desired dielectric constants

Rapidly advancing computer technology has demonstrated great potential in recent years to assist in the generation and discovery of promising molecular structures. Herein, we present a data science-centric "Design-Discovery-Evaluation" scheme for exploring novel polyimides (PIs) with desired dielectric constants (ε). A virtual library of over 100 000 synthetically accessible PIs is created by extending existing PIs. Within the framework of quantitative structure-property relationship (QSPR), a model sufficient to predict ε at multiple frequencies is developed with an R 2 of 0.9768, allowing further high-throughput screening of the prior structures with desired ε. Furthermore, the structural feature representation method of atomic adjacent group (AAG) is introduced, using which the reliability of high-throughput screening results is evaluated. This workflow identifies 9 novel PIs (ε >5 at 103 Hz and glass transition temperatures between 250 °C and 350 °C) with potential applications in high-temperature capacitive energy storage, and confirms these promising findings by high-fidelity molecular dynamics (MD) simulations.

Hydroxyl-Amide Alkaloids from Pepper Roots: Potential Sources of Natural Antioxidants and Tyrosinase Inhibitors

Pepper (Piper nigrum L.) is a widely used spice plant known for its fruits and roots, which serve as flavor enhancers in culinary applications and hold significant economic value. Despite the popularity of pepper fruits, their roots remain relatively understudied, with limited research conducted on their bioactive components. This study focused on discovering and separating the primary bioactive amide alkaloids found in pepper roots. The process involved using the antioxidant activity of crude fractions and the Global Natural Products Social Molecular Networking analysis platform. The process led to the discovery of 23 previously unknown hydroxyl-amide alkaloids. Notably, compounds 11, 12, and 14 showed excellent antioxidant activity, while compound 11 exhibited significant inhibitory effects on mushroom tyrosinase. Theoretical exploration of enzyme-ligand interactions was conducted through molecular docking and molecular dynamics simulation. The findings of this study highlight the potential of hydroxyl-amide alkaloids as antioxidant products and natural food preservatives in the pharmaceutical and food cosmetic industries.

Synthesis of High-Performance Colorless Polyimides with Asymmetric Diamine: Application in Flexible Electronic Devices

Colorless polyimides (CPIs) are widely used as high-performance materials in flexible electronic devices. From a molecular design standpoint, the industry continues to encounter challenges in developing CPIs with desired attributes, including exceptional optical transparency, excellent thermal stability, and enhanced mechanical strength. This study presents and validates a method for controlling 2-substituents, with a specific emphasis on examining how these substituents affect the thermal, mechanical, optical, and dielectric characteristics of CPIs. The presence of two CF3 groups on the same side of the diamine structure ensured the transmittance of the film. The charge transfer effect and the molecular distance are dynamically regulated by changing the 2-substituent (-OCH3/-CH3/H/F). The polyimide exhibited a well-maintained equilibrium between transparency and thermal stability, with a T500nm value ranging from 86.2 to 89.6% in the visible region, and a glass transition temperature (Tg) ranging from 358.6 to 376.0 °C. Additionally, the 6FDA-2-MTFMB compound, when combined with methyl, excels as a protective layer and base material, exhibiting excellent performance in various aspects. It has been verified as an appropriate option for flexible photodetectors and wearable piezoresistive sensors. In summary, this systematic investigation will provide a comprehensive and demonstrative methodology for developing CPIs that are capable of adapting to flexible electronic devices.

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

The design of high-performance polyimide (PI) films and understanding the relationship of the structure-dielectric property are of great significance in the field of the microelectronics industry, but are challenging. Herein, we describe the first work to construct a series of novel tert-butyl PI films (denoted as PI-1, PI-2, PI-3, and PI-4) based on a low-temperature polymerization strategy, which employed tetracarboxylic dianhydride (pyromellitic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, 4,4'-diphenyl ether dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic anhydride) and 4,4'-diamino-3,5-ditert butyl biphenyl ether as monomers. The results indicate that introducing tert-butyl branches in the main chain of PIs can enhance the free volume of the molecular chain and reduce the interaction between molecular chains of PI, resulting in a low dielectric constant. Particularly, the optimized PI-4 exhibits an excellent comprehensive performance with a high (5) wt% loss temperature (454 °C), tensile strength (117.40 MPa), and maximum hydrophobic angle (80.16°), and a low dielectric constant (2.90), which outperforms most of the results reported to date.

Density Functional Theory-Based Approach For Dielectric Constant Estimation of Soluble Polyimide Insulators

Evaluation of the insulating properties of polymers, such as the dielectric constant and dissipation factor, is crucial in electronic devices, including field-effect transistors and wireless communication applications. This study applies density functional theory (DFT) to predict the dielectric constant of soluble polyimides (SPIs). Various SPIs containing trifluoromethyl groups in the backbone with different pendant types, numbers, and symmetries are successfully synthesized, and their dielectric constants are evaluated and compared with the DFT-estimated values. Two types of DFT-optimized SPIs, single-chain and stacked-chain models, are used to describe the local geometries of the SPIs. In addition, to reveal the relationship between the molecular structure and dielectric constant, further investigations are conducted by considering the dielectric constant of composing ionic and electronic components. The DFT-estimated static dielectric constant of the single-chain model accurately reproduces the corresponding experimental value with at least 80% accuracy. Our approach provides a rational and accelerated strategy to evaluate polymer insulators for electronic devices based on cost-effective DFT calculations.

Preparation and Properties of Intrinsically Black Polyimide Films with CIE Lab Color Parameters Close to Zero and High Thermal Stability for Potential Applications in Flexible Printed Circuit Boards

Black polymer films with high thermal stability are highly desired in flexible electrical and electronic fields. Conventional black polymer films based on high-temperature resistant polymers and black inorganic dyes are usually suffered from the poor electrical and tensile properties. In the current work, a series of intrinsically black polyimide (BPI) films with International Commission on Illumination (CIE) Lab optical parameters close to zero and high thermal stability have been designed and prepared. For this purpose, an electron-rich aromatic diamine, 4,4′-iminodianiline (NDA), was copolymerized with 1,4-phenylenediamine (PDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (sBPDA) to afford a series of poly(amic acid) (PAA) solutions, which were then thermally dehydrated to provide the final BPI films at elevated temperatures up to 400 °C in air. The molar fraction of NDA in the total diamine monomers was 0 for BPI-0 (sBPDA-PDA), 10% for BPI-1, 20% for BPI-2, 30% for BPI-3, 40% for BPI-4, 50% for BPI-5, and 100% for BPI-6. For comparison, two referenced polyimide (PI) films, including PI-ref1 and PI-ref2, were prepared according to a similar procedure. The former was derived from pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) and the latter was from PMDA and NDA. The BPI films exhibited an increasing degree of blackness with the increasing contents of NDA units in the polymer films. For example, the BPI-6 (sBPDA-NDA) film exhibited the optical transmittance of 1.4% at a wavelength of 650 nm (T₆₅₀), which was obviously lower than those of PI-ref1 (T₆₅₀ = 74.6%) and PI-ref2 (T₆₅₀ = 3.6%). In addition, the BPI-6 film showed the CIE Lab parameters of 0.39 for L*, 2.65 for a*, 0.66 for b*, and haze of 1.83, which was very close to the criterion of “pure blackness” for polymer films (L* = a* = b* = 0). At last, incorporation of the NDA units in the rigid-rod BPI-0 (BPDA-PDA) film slightly deteriorated the high-temperature dimensional stability of the derived BPI films. BPI-6 film showed a linear coefficient of thermal expansion (CTE) value of 34.8 × 10⁻⁶/K in the temperature range of 50 to 250 °C, which was higher than those of the BPI-0 (CTE = 12.3 × 10⁻⁶/K), PI-ref1 (CTE = 29.5 × 10⁻⁶/K), and PI-ref2 (CTE = 18.8 × 10⁻⁶/K) films. Nevertheless, the BPI films maintained good thermal stability with the 5% weight loss temperatures (T_5%) higher than 590 °C, and the glass transition temperatures (T_g) higher than 340 °C.

Perfluorocyclobutyl-containing transparent polyimides with low dielectric constant and low dielectric loss

The combination of loose chain packing and high fluoro content endows PFCB-containing polyimides with excellent optical transparency and dielectric properties.