Papers by Keyword: Polyimide

Abstract: A kind of Polyimide films (PI films) containing biphenyl and bis-benzimidazole rings were prepared from the its precursor Polyamic acid (PAA) solution synthesized by aromatic diamine containing biphenyl and bis-benzimidazole rings with different commercial aromatic dianhydrides. The PI films exhibited excellent hydrophobicity with the contact angle of higher than 90o and the hydroscopicity are lower than 1%. The PI films also have great dielectric properties of the dielectric constant ranges from 2.10 to 2.94 under the voltage frequency within 1 to 10⁶ H_Z.

Abstract: Neural probe array is utilized in neural recording, in the aim to understand the neural activity. Silicon is the common substrate used in neural probe array. However, due to the rigid nature, the silicon-based neural probe array causes cell damage during implantation into the brain tissue. This would reduce the signal-to-noise ratio. Therefore, flexible polymer probe is more suitable as it can help to minimize the tissue damage and thus increasing the signal-to-noise ratio. The lack of stiffness for the flexible probe is solved by coating it with polyethylene glycol (PEG). It stiffens the probe and can be dissolved in water, which allows the polymer probe to regain its flexibility. The proposed integrated probe with reduced distance between probe and ASIC will further help to improve the signal-to-noise ratio during neural recording. The coated flexible probe regained original impedance of 14.1 kΩ at a frequency of 1 kHz. A bench-top neural recording with the flexible probe array in saline solution will also be acquired.

Abstract: In recent years, the utilisation of ionic liquids supported on porous polymer membranes has been demonstrated to enhance gas separation performance by improving both permeability and selectivity for several industrially-relevant gas mixtures. However, the use of such supported ionic liquid membranes (SILMs) is normally not feasible at elevated process temperatures due to the resulting decrease in ionic liquid viscosity, which can lead to increased loss of ionic liquid from the membrane support during operation. In addition, many of the polymer membranes typically used in SILMs exhibit relatively poor mechanical and thermal stabilities at high temperatures. To overcome these problems associated with SILMs, thermally-stable composite ionic liquid and polymer membranes (CILPMs) have been fabricated in this study, thus exploiting the beneficial properties of ionic liquids for gas separation at elevated temperatures. Poly (pyromellitimide-co-4,4-oxydianiline) (PMDA-ODA PI) in combination with the ionic liquid, [C₄mi [NTf₂] were used to fabricate the CILPMs. A measurement rig was designed and built to determine permeabilities and selectivities of the CILPMs for H₂, N₂, CO, CO₂ and CH₄ over a range of pressures and temperatures. The fabricated CILPMs were shown to maintain excellent mechanical and thermal stability over a wide range of processing conditions. Temperature was shown to greatly affect both permeability and selectivity of the membranes, whilst pressure had less influence. The incorporation of [C₄mi [NTf₂] into the membranes was found to significantly increase CO₂ permeation and, therefore, it is anticipated that these CILPMs hold significant potential for CO₂ separation applications.

Abstract: Polyimide (PI) was chosen as the matrix of the composites, barium titanate/polyimide (BT/PI) nanocomposite films were prepared with in-situ polymerization. The morphology of the samples was obtained by SEM. The factors affecting the dielectric properties are discussed. When the mass fraction of BT is 70%, the dielectric constant will be 19.32, and loss 0.00254 (at 10³ Hz). The optimal solvent content and ultrasonic time were 9.2 ml and 30 min respectively. TG analysis shows that the film is stable below 500°C. The AC breakdown strength were 42 MV·m^-1 and 64 MV·m^-1 for 70% BT/PI and 60% BT/PI respectively, and corresponding energy storage density were 0.17 J·cm^-3 and 0.30 J·cm^-3 respectively.

Abstract: Effects of atomic oxygen (AO) irradiation on the structural and tribological behaviors of MoS₂ filled polyimide (PI) composites were studied by using ball-on-disc tribometer, infrared spectra, X-ray photoelectron spectroscopy and scanning electron microscopy. It was found that the irradiation of AO induced the destruction of polymer molecular structures and formation of volatile products which induced the change of the structure, morphology and tribological properties of samples. The addition of MoS₂ filler significantly increased the AO resistance of PI composites due to the formation of MoO₃-rich skin layers during AO process. The addition of MoS₂ improved the tribological properties of PI before and after AO irradiation.

Abstract: A new microwave imidization method was used to prepare polyimide (PI) film in this paper. FT-IR spectrum and ultraviolet absorption spectrum are measured to study the chemical structure and optical properties of this film. The FT-IR spectrum shows that the characteristic imide groups are observed at the peaks of 727.18 cm^-1, 1379.67 cm^-1 and 1776.51 cm^-1, which confirmed imide formation. The ultraviolet absorption spectrum reveals that optical band gap of the PI is about 2.64 eV.

Abstract: In this paper, a series of polyimide (PI) films with different monomer mole ratios between PMDA and ODA (0.980: 1, 0.990: 1, 1.000: 1, 1.010: 1 and 1.015: 1) were prepared in order to investigate the effect of molecular weight on optical properties. Inherent viscosity values were taken as a measure of the molecular weight. The fluorescence properties of the PI films have been measured. The fluorescence spectra show that three obvious emission peaks can be observed at 583 nm (1.00 dL/g), 594 nm (1.42 dL/g) and 603 nm (1.57 dL/g) respectively. In addition, emission peaks show red-shift with the increase of molecular weight, which can attribute to the decease of orbital energy caused by conjugated effect.

Abstract: CP2 polyimide (prepd. from 6FDA and 1,3-bis (3-aminophenoxy) benzene) was blended with (1-50 wt.%) detonation nanodiamonds (DND, pristine, acetone-washed, and 4-(2,4,6-trimethylphenoxy) benzoic acid-functionalized), and the blends were evaluated as thin films for its potential utility in high-energy-density capacitors that would have stable dielectric properties over a wide temperature range (-55 to 300°C) and at frequencies up to or greater than 100 kHz. Both the dielectric storage and loss increased substantially with DND content. Surface functionalization (with the above benzoic acid derivative) significantly reduced the dielectric loss, while the use of acetone-washed DNDs had no effect on the dielectric loss. DND was also blended with CP2 via in-situ polymerization and found to have little effect on the dielectric properties.

Abstract: Graphene/polyimide nanocomposites with different weight loadings were prepared by a solution compounding technique. Graphene was synthesized from graphite oxide that was fabricated by the Hummers method. X-ray diffraction (XRD), ultraviolet visible (UV-vis) spectra and simultaneous thermal analysis were used for the microstructure analysis of the graphenes. Graphenes with single layer structure were synthesized successfully and had good solubility in water or other polar solvents due to a few functional groups on the graphene carbons. Graphenes have good thermal stability. Mechanical and tribological properties were studied for the graphene/polyimide composites. The composites have excellent strength and toughness with very small graphene loading level and the addition of graphene decreased the friction coefficient and wear rate of the composites.

Abstract: The surface binding energy between the polyimide(PI) and zinc oxide (ZnO) have been simulated using the molecular dynamics theory.The PI / ZnO model has been established by using Forcite program package of Materials Studio software.The total atoms number about 300 million, the radius of the nano-ZnO cluster model have five groups are respectively 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm.The effect of different particle size of nano-ZnO on surface binding energy in PI / ZnO composites was investigated. The relationship between the surface binding energy of PI / ZnO composites and the nano-Zno radius, the maximum of surface binding energy were obtained. The computed results show that the intermolecular bonds between nano-ZnO and PI are mainly van der waals bonds.And the surface atomic number of nano-ZnO increases along with the increasing of nano-ZnO radius, indicating that the increasing of contact surface between the nano-ZnO and PI, which lead to the surface binding energy increases, the total energy lower and the system more stable.