Synthesis and characterization of colorless polyimide nanocomposite films containing pendant trifluoromethyl groups

Highly Self-Healable Polymeric Coating Materials Based on Charge Transfer Complex Interactions with Outstanding Weatherability

In this study, we prepare highly self-healable polymeric coating materials using charge transfer complex (CTC) interactions. The resulting coating materials demonstrate outstanding thermal stability (1 wt% loss thermal decomposition temperature at 420 °C), rapid self-healing kinetics (in 5 min), and high self-healing efficiency (over 99%), which is facilitated by CTC-induced multiple interactions between the polymeric chains. In addition, these materials exhibit excellent optical properties, including transmittance over 91% and yellow index (YI) below 2, and show enhanced weatherability with a ΔYI value below 0.5 after exposure to UV light for 72 h. Furthermore, the self-healable coating materials developed in this study show outstanding mechanical properties by overcoming the limitations of conventional self-healing materials.

Effects of diamine isomers on the properties of colorless and transparent copoly(amide imide)s

To fully understand the structure–property relationship of aromatic copoly(amide-imide)s (Co-PAIs) and determine which factors lead to chain rigidity, we prepared two series of Co-PAIs. They were synthesized from two types of amine monomers containing m- and p-isomers and different ratios of 4,4′-(hexafluoroiso-propylidene)diphthalic anhydride (6FDA) and 4,4′-biphthalic anhydride (BPA). m-Substituted and p-substituted N,N′-[2,2′-bis(trifluoromethyl)-4,4′-biphenylene]bis(aminobenzamide) (MPAB) diamine isomers were synthesized from 3- and 4-nitrobenzoyl chloride and 2,2′-bis(trifluoromethyl) benzidine (TFB), respectively. The Co-PAI films were synthesized from poly(amic acid) (PAA), via solution-casting, followed by thermal imidizations. The thermal- and mechanical-properties and optical transparency of the Co-PAI films with different BPA monomer contents were investigated. We also investigated the effects of the different MPAB isomers on the Co-PAI structures. Compared with the m-substituted MPAB Co-PAI films, the p-substituted MPAB Co-PAI films have superior thermo-mechanical properties at the same monomer content. However, the optical transparencies of the m-MPAB Co-PAIs are slightly better than those of the p-MPAB Co-PAIs.

The thermal- and mechanical-properties and optical transparency of the copoly(amide imide) films with different BPA monomer contents were investigated.

Indium Tungsten Oxide Thin Films for Flexible High-Performance Transistors and Neuromorphic Electronics

Thin-film transistors (TFTs) with high electrical performances (mobility > 10 cm²/V s, V_th < 1 V, SS < 1 V/decade, on/off ratio ≈ 10⁶) obtained from the silicon- and oxide-based single-crystalline semiconductor materials require high processing temperature and hence are not suitable for flexible electronics. Amorphous oxide-based transparent electronic devices are attractive to meet emerging technological demands where crystalline oxide-/silicon-based architectures cannot provide a solution. Here, we tackle this problem by using a novel amorphous oxide semiconducting material-namely, indium tungsten oxide (IWO)-as the active channel in flexible TFTs (FTFTs). Post-annealing temperature as low as 270 °C for amorphous IWO thin films deposited by radio frequency sputtering at room temperature could result in smooth morphology ( R_rms ≈ 0.42 nm), good adhesion, and high carrier density ( n ≈ 7.19 × 10¹⁸ cm^-3). Excellent TFT characteristics of flexible devices could be achieved with linear field effect mobility μ_FE ≈ 25.86 cm²/V s, subthreshold swing SS ≈ 0.30 V/decade, threshold voltage V_th ≈ -1.5 V, and on/off ratio I_on/ I_off ≈ 5.6 × 10⁵ at 3 V and stable operation during bending of the FTFT. Additionally, IWO TFTs were implemented as synapses, the building block for neuromorphic computing. Paired-pulse facilitation up to 138% was observed and showed an exponential decay resembling chemical synapses. Utilizing this characteristic, a high-pass dynamic temporal filter was devised providing increased gain from 1.55 to 21 when frequency was raised from 22 to 62 Hz. The high performance and stability of flexible TFTs obtained with IWO films demonstrate their promise for low-voltage electronic applications.

Mixed Rigid and Flexible Component Design for High-Performance Polyimide Films

To develop the polyimide (PI) which is closely matched to the coefficient of the thermal expansion (CTE) of copper, a series of PIs are prepared from 5,4′-diamino-2-phenyl benzimidazole (DAPBI), 4,4′-diaminodiphenyl ether (ODA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) using a sequential copolymerization, blade coating, and thermal imidization process. The physical properties of the PIs are effectively regulated and optimized by adjusting the ratio of the rigid DAPBI and flexible ODA components. By increasing the DAPBI content, thermal stability, dimensional stability, and mechanical properties, the resultant polymer is enhanced. PI-80 exhibits an excellent comprehensive performance, a glass transition temperature of 370 °C, and a tensile strength of 210 MPa. Furthermore, the CTE as calculated in the range 50–250 °C is ca. 19 ppm/K, which is equal to that of copper. A highly dimensionally stable, curl-free, and high T-style peel strength (6.4 N/cm) of copper/PI laminate was obtained by casting the polyamic acid onto copper foil (13 μm) and thermally curing at 360 °C, which indicates that it has the potential to be applied as an electronic film for flexible displays and flexible printed circuit boards. A structural rationalization for these remarkable properties is also presented.

High-mobility ZrInO thin-film transistor prepared by an all-DC-sputtering method at room temperature

Thin-film transistors (TFTs) with zirconium-doped indium oxide (ZrInO) semiconductor were successfully fabricated by an all-DC-sputtering method at room temperature. The ZrInO TFT without any intentionally annealing steps exhibited a high saturation mobility of 25.1 cm²V⁻¹s⁻¹. The threshold voltage shift was only 0.35 V for the ZrInO TFT under positive gate bias stress for 1 hour. Detailed studies showed that the room-temperature ZrInO thin film was in the amorphous state with low carrier density because of the strong bonding strength of Zr-O. The room-temperature process is attractive for its compatibility with almost all kinds of the flexible substrates, and the DC sputtering process is good for the production efficiency improvement and the fabrication cost reduction.

Flexible polyimide films hybrid with functionalized boron nitride and graphene oxide simultaneously to improve thermal conduction and dimensional stability

Coupling agent-functionalized boron nitride (f-BN) and glycidyl methacrylate-grafted graphene (g-TrG) are simultaneously blended with polyimide (PI) to fabricate a flexible, electrically insulating and thermally conductive PI composite film. The silk-like g-TrG successfully fills in the gap between PI and f-BN to complete the thermal conduction network. In addition, the strong interaction between surface functional groups on f-BN and g-TrG contributes to the effective phonon transfer in the PI matrix. The thermal conductivity (TC) of the PI/f-BN composite films containing additional 1 wt % of g-TrG is at least doubled to the value of PI/f-BN and as high as 16 times to that of the pure PI. The hybrid film PI/f-BN-50/g-TrG-1 exhibits excellent flexibility, sufficient insulating property, the highest TC of 2.11 W/mK, and ultralow coefficient of thermal expansion of 11 ppm/K, which are perfect conditions for future flexible substrate materials requiring efficient heat dissipation.