PI Film Research Articles

Amorphous Co–Pi anchored on CdSe/TiO2 nanowire arrays for efficient photoelectrochemical hydrogen production

Photoelectrochemical (PEC) water splitting into hydrogen and oxygen using hybridized semiconductor photoelectrodes has become a promising strategy for converting solar energy into clean and sustainable H2 fuel. Here, we report a promising hybrid photoanode constructed by electrodepositing an amorphous Co–Pi film onto semiconducting CdSe/TiO2 nanowire arrays for photoelectrochemical hydrogen production. This photoanode exhibits a high water-splitting photocurrent density, which is attributed to the broad visible light absorption and efficient charge carrier separation by the virtue of the type-II heterojunction formed between TiO2 and CdSe. Photoconversion efficiency of Co–Pi/CdSe/TiO2 and CdSe/TiO2 photoanodes increase by 3.3 and 2.1 times, compared with the pristine TiO2 photoanode. Moreover, Co–Pi/CdSe/TiO2 photoelectrode shows greatly improved PEC stability, the drop in photocurrent of Co–Pi/CdSe/TiO2 nanowire arrays photoelectrode is about 10% after 1 h illumination, because of the addition of the Co–Pi film protecting the light absorber CdSe/TiO2 from photocorrosion. The enhanced PEC performance mechanism of triple hybrid photoanode is also discussed in this paper.

The In-plane Orientation and Thermal Mechanical Properties of the Chemically Imidized Polyimide Films

The thermal and mechanical properties of the chemically imidized polyimide (CIPI) films and thermally imidized polyimide (TIPI) films were investigated systematically. Experimental results indicated that the CIPI films show dramatically enhanced tensile strength and modulus with obviously reduced coefficient of thermal expansion (CTE) in comparison with TIPI films. These enhancements results from the high in-plane orientation and close packing of the CIPI backbones. Compared with thermal imidization which starts at about 140 °C, the chemical imidization activated by acetic anhydride and isoquinoline initiates the cyclization even at room temperature. The resulting imide rings restrict the mobility of polymer chains and lead to the in-plane orientation with solvent evaporation. Additionally, fewer small molecules remain in the films after treated at 120 °C by chemical imidization than by thermal imidization. The polymer chain plasticization caused by the evaporation of small molecules at high temperature is obviously restricted. Moreover, the partially imidized polymer inhibits the decomposition of mainchains that occurs at subsequent high temperature process, being beneficial to the formation of high molecular weight PI films. Hence, chemical imidization pathway shows apparent advantage to produce PI films with great combined properties, including high modulus, strength and toughness, as well as high thermal dimension stability etc.

A flexible three-dimensional force sensor based on PI piezoresistive film

In this paper, a flexible three-dimensional (3D) force sensor utilizing the piezoresistive principle has been manufactured. The proposed sensor is designed as four pressure sensing resistors embedded in a flexible substrate. The piezoresistive PI film is used to be sensing material, as its effective pressure sensitivity, good linearity, and low hysteresis. The bump built on top of the sensor convert an applied force to the mechanical stress, and changes the resistances of the four sensing cells. The normal and shear forces can be therefore detected by the resistance responses. Calibration and test experiments have been conducted to characterize the 3D force sensor. The results demonstrate that the sensor is capable of 3D force measurement with good linear responses and sensitivity. The proposed 3D force sensor could be suitable for tactile sensing in intelligent robots, and other applications requiring three-dimensional force detection.

Phosphinated polyimide hybrid films with reduced melt-flow and enhanced adhesion for flexible copper clad laminates

Adhesion properties of phosphinate-contained polyimide (P-PI) hybrid films were studied to develop suitable heat resistant adhesive film with excellent hot-melt processability. The diamine, 1,1-bis(4-aminophenyl)-1-(6-oxido-6H-dibenz<c, e><1, 2> oxaphosphorin-6-yl) ethane (i.e. DMA), was introduced to synthesize a series of P-PI films with different contents of DMA. The presence of the bulky phosphinate pendant group on PI backbone increased the adhesion strength and effectively reduced the melt flow after hot-pressing to flexible copper clad laminates (FCCL) without the usage of adhesive. The P-PI film tended to produce rougher surface that facilitated the mechanical interlocking effect between P-PI hybrid film and copper. The presence of characteristic phosphinate functional groups and the formation of polyphosphate layer on P-PI film were confirmed by FTIR and XPS results. The storage modulus and glass transition temperature of P-PI films were increased because of the enhanced rigidity by phosphinate groups. The presence of bulky phosphinate pendant group also reduced the coefficient of thermal expansion and dielectric constant of PI films. Although the introduction of phosphinate in PI reduced the initial weight loss temperature, the thermal stability of P-PI films was sufficient for the following manufacturing processes. Furthermore, another interesting observation was the enhancement of transparency at 400 nm for P-PI. Those properties make P-PI films useful in FCCL application.

(Invited) Printed Flexible Pressure Sensor Driven by OTFT Array

We have constructed an all printed electronics device manufacturing line and fabricated an organic TFT array on a flexible film substrate. In the automated and continuously operated manufacturing line, we used the reverse offset printer for electrode pattern, digital inkjet printer for organic semiconductor layer, slit-die coater for insulator layer, and gravure offset printer for pixel electrode, specified printer for pressure sensitive layer. The printed pattern with high resolution and high accuracy can be obtained on a flexible film, not only PI, PEN but PET film substrate in low process temperature. The all-printed organic TFT array back-plane is applied to the flexible and light-weight pressure sensor which is driven in active matrix mode. As an example, we demonstrated the compact cylindrical pressure sensor with bare-chip driver ICs at international nanotechnology exhibition in 2018 as shown in lower photo. By taking an advantage of the flexible lightweight and high resolution characteristics of sensors, we are continuing some kinds of field testing in field of healthcare-related applications of rehabilitation and nursing care support and also shelf management system at a convenient store. Furthermore we are challenging the development of robot skin which has sensors as sensitive as human touch. Compact cylindrical pressure sensor demonstrated at international nanotechnology exhibition in 2018. Figure 1

Effect of aging time on the dielectric properties of PI/CCTO composite thin films

In this paper, Pyromellitic diancomposite (PMDA) and 4,4-Oxydianiline (ODA) were selected as the monomers and CaCu3Ti4O12 (CCTO) particles were used as filler to synthesize the PI/CCTO composite film by the in situ polymerization. The phase composition and dielectric property of the composites were analyzed and tested by XRD and a broadband dielectric spectral instrument. The effects of aging time on the dielectric properties of PI and PI/CCTO composite films were researched. Results show that the aging time can improve the dielectric property of the PI composite film and the optimal aging time is 24h. The PI/CCTO composite film plays the minimum value of the loss tangent about 0.022 and the maximum value of the dielectric constant about 8.8 at 100Hz, which is 1.6 times larger than that of PI film.

Ternary memory property of novel polyimide with backbone carbazole moiety and pendant triphenylamine moiety

The polyimide (TPA-Cz PI) was synthesized by the reaction of 9-(4′-(4′-diphenylamino)phenylbenzyl)-3,6-diaminocarbazole with 2,2′,3,3′-biphenyltetracarboxylic dianhydride through a classical two-step polymerization process. It exhibited excellent organo-solubility and self-extinguishing property. The synthesized TPA-Cz PI shown excellent film formation. The TPA-Cz PI film sandwiched between an indium tin oxide bottom electrode and Al top electrode. And the fabricated memory device exhibited ternary rewritable storage property in the bias with good data retention and the current ratio of 104:102:1 for ON2, ON1, and OFF states. Its current conduction mechanism by the I-V curves of different conduction models based on the experimental data was analyzed and used to illuminate the physical nature of resistance switching effects. The experimental result indicates that field-induced conformational ordering of the TPA-Cz PI chains and charge-transfer interaction between electron-donor and electron-withdrawing are responsible for the switching behavior. This work can provide a sketch for the design and selection of ternary state resistance random access memory materials in future research.

P‐134: Lamination Contact Bonding and Mechanical Detaching of PI Film for Manufacturing of Flexible OLED Displays

In this work, we attempted to develop a new PI film bonding and mechanical detaching process which may be capable of replacing conventional PI film forming process, i.e., vanish coating followed by a thermal curing process and then laser lift‐off process. The new process developed showed that the mechanical detaching force is similar to that of laser lift‐off process.

P‐130: Reliable Flexible Elevated Metal Metal‐Oxide IGZO TFTs

Flexible EMMO IGZO TFTs fabricated on 20 µm thick PI film are reported here. The utilized technology results in high electrical stability, of devices, combined to high robustness against mechanical deformation down to 3%.

Enhanced thermal and electrical insulation properties of polyimide films determined via a two‐dimensional layered double hydroxide–potassium perfluorooctane sulfonate material

ABSTRACTPolyimide (PI) films used in aerospace and rail applications are degraded by thermal, chemical, and electric power under the effect of insulation aging. To prevent these types of degradation, we prepared nanocomposite films of PI and layered double hydroxide (LDH) modified with the potassium perfluorooctane sulfonate (FS) by an in situ method. On the whole, the glass‐transition temperature, dielectric constant (ɛ′), and corona‐resistance lifetime of the nanocomposite films increased over those of the pure PI film, but the temperature at 10 wt % weight loss, breakdown strength, and volume resistance decreased correspondingly as a whole. The PI matrix was protected by the inorganic material of LDH–FS with a high ɛ′ from corona corrosion. Furthermore, the heat and chemical interactions of the composite films improved the corona‐resistance lifetime, despite the decrease in the breakdown strength; this should result in promising applications for insulation parts of variable‐frequency motors. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46528.

Temperature effect on electrical characteristics of negative DC corona charged polyimide films

The study of the effect of sample temperature on the electric properties of PI films has been investigated. Surface potential decay (SPD) measurements on PI (Kapton HN, thickness: 50 μm) films were measured, after negative corona discharge, as a function of sample temperature varying from 27 to 80 °C. The measurements showed significant increase in the SPD rate with increasing sample temperature. Surface potential profile, return potential appearing after charge neutralization and charging current characteristics have been experimentally recorded for different sample temperatures in order to interpret SPD evolution at high sample temperature. The SPD curves were analyzed by fitting a bi-exponential decay Equation according to the presence of two different decay mechanisms related to shallow and deep traps. The distributions of trapped charges are obtained for different sample temperatures.

Effect of interface structure regulation caused by variation of imidization rate on conduction current characteristics of PI/nano-Al2O3 three-layer composite films

A series of sandwich structure PI films were prepared by different imidization process, with pure PI film as the interlayer and PI/Al2O3 composite films as outer layers. The imidization rate of the film with different cured processes was calculated by characterizing by infrared spectrum (FT-IR), and the morphology of interlayer interface with different imidization rates by scanning electron microscope (SEM). When the imidization conditions of the first and second films were 260 °C/120 min, the composite films displayed better interface structure and higher imidization rate (ID) than others. Moreover, results also showed that the conduction current of three-layer composite film steadily improved with increased ID and temperature, and was higher than that of the pure film. At the temperature of 30 °C, the electrical aging threshold at different ID was obtained. When the ID reached the maximum value of 78.9%, the electrical aging threshold reached the maximum 41.69 kV/mm.

Laser emission characteristics of the capillary of dye-doped liquid crystal

The dye doped liquid crystal filling tunable laser has been widely adopted in many areas, such as optical communication, sensor and medical imaging with a low cost. The temperature-sensitive refractive indice of liquid crystal makes it a filling material suitable for being used in the capillary. The existing studies have introduced the liquid crystal filled with capillary, which has the complicated craft and big cost. As is well known, the capillary has the advantages of the easy preparation and low cost, but the liquid crystal filled capillary based dye doped liquid crystal filling tunable laser is rarely studied. Dye-doped cholesteric liquid crystal (CLC) based tunable laser has many advantages such as small-size, low-threshold, high-efficiency, wide-tunability with wavelength varying from ultraviolet to infrared. So It shows great promise in applications of single-chip experiment, biological identification and sensor. To develop high-efficiency dye-doped CLC tunable lasers for different potential applications, it is crucial to explore their emission performances in three laser emission modes:distributed feedback (DFB), whispering gallery modes (WGMs) and random laser (RL). We theoretically propose and experimentally demonstrate the characteristics of laser emission based on dye-doped CLC in capillary tubes which are treated with the photo-alignment PI films. Firstly, we prepare capillary tubes filled with dye-doped CLC with three inner diameters of 100 m, 200 m and 300 m. By using a double-frequency Nd:YAG 532 nm laser as a pump source, the emission spectra, energy thresholds and temperature dependent tunabilities in the cases with and without PI films are analyzed, respectively. It is clearly shown that dye-doped CLC in the capillary with the PI films generate DFB-mode lasing and WGMs lasing. Experimental results show that the capillaries with thinner-inner diameters and PI films have lower emission threshold energies than without PI films, the former threshold can be reduced to as low as 4.5 J mm-2. Meanwhile, with temperature increasing, the DFB wavelength is blue-shifted, resulting in a central wavelength tuning range of 5.9 nm. Then high performance WGM with an FSR of 1.05 nm is created when the temperature is increased up to as high as 43 ℃. It can be found that the laser emission with photo-alignment PI films shows an optimum RL mode with less laser emission peaks than the laser emission without photo-alignment PI films. In this work we propose and demonstrate that a capillary based dye-doped CLC tunable laser with photo-alignment PI films can easily work with three emissions:DFB-mode, WGMs or RL by changing optical field and the applied temperature. The above research results provide valuable clues and methods to develop high-quality dye-doped CLC based tunable laser, filter, optical switch and sensor.

Transition metal doping effects in Co-phosphate catalysts for water splitting studied with XAS

Metal oxides as oxygen evolution reaction (OER) catalysts for water splitting are ubiquitous in research and application. Pure and doped (or hybrid) Co oxide systems are of particular interest due to their good efficiency. However, the electronic effects of different dopants are still unclear in many of these systems. We present a study of doped Co-phosphate (Pi) films deposited electrochemically from aqueous solutions of neutral pH using an X-ray absorption spectroscopy (XAS), a technique that can reveal important information about catalytically active states. These hybrid films, obtained from solutions containing both Co ions and another transition metal (TM) ion (TM=Mn, Fe, Ni), were analyzed with XAS at the TM L-edges and the O K-edge. We find that a large concentration of Co3+-ions in the films and a low-lying edge of the O 2p conduction band (CB) are good indicators for the OER efficiency of the films. Our results show that native Co-Pi is close to optimal for the OER activity at low deposition potential. However, Mn- and Ni-doped systems have promising properties when deposited at higher potentials because these ions tend to stabilize the Co3+-state in the films as well as the position of the O 2p-edge CB (a few tenths of 1eV), in contrast to native Co-Pi films.

Polymerization of poly-(amic acid) ammonium salt in aqueous solution and its use in flexible printed circuit boards

It is highly desirable to combine the solubility of the PI precursor in a non-polluting solvent with the high performance behavior of PIs without sacrificing processability, thermal properties and mechanical properties. In this study, we explored a new strategy based on polycondensation reactions to prepare poly-(amic acid) ammonium salt (PAAS) in aqueous solution. PAAS was synthesized using a mixture of 3,3,4,4-biphenyltetracarboxylic dianhydride and 4,4′-oxydiphthalic anhydride and a mixture of 4,4′-diaminodiphenyl ether and p-phenylenediamine. The molecular weight of PAAS, the inherent viscosity of the PAAS solution, and the thermal and mechanical properties of the obtained PI films were investigated by focusing on the polymer structures and comparing with those of the polymerization in N,N-dimethylacetamide. The PI films produced via the different polymerization methods had almost the same thermal properties. Adhesion properties of flexible copper-clad laminates (FCCLs) which were influenced by the plastic deformation and the interface condition that was investigated using Fourier-transform infrared microspectroscopy, were investigated using the peel strength test. The peel strength of the FCCLs changed little between room temperature and 200°C, and this indicates that the obtained film that prepolymerized in aqueous solution can potentially be used for FCCLs at high temperature in the microelectronics industry.

New Synthetic Approach of Fluorine-Containing Graphene Oxide for Improving Dielectric and Mechanical Properties of Polyimide Composites

A new approach to synthesize fluorine-containing graphene oxide (FCGO) was proposed, in which a less toxic reagent was used rather than fluorine gas or anhydrous hydrogen fluoride. The dielectric and mechanical properties of polyimide composites were improved by incorporating a small amount of FCGO. FCGO served as not only nanofiller to lower the dielectric constant of PI films but also inorganic toughening particles to improve the toughness of PI films. The dielectric constant of PI films with 0.6 wt % FCGO was decreased from 3.33 for pure PI to 2.34. In addition, both the tensile strength and Young’s modulus of PI films with 0.6 wt % FCGO were increased to 141 MPa and 4.95 GPa from 118 MPa and 2.81 GPa for pure PI, respectively. In addition, its tensile energy to break was enhanced to 31.6 MJ/m3 from 20.8 MJ/m3.

Effect of Alkali Treatment on the Mechanical Property of Polyimide Film

Polyimide films treated with an alkali and ion exchange undergo surface-confined hydrolysis to produce polyimide composites. On the other hand, it is unclear what impact this method has on the mechanical properties of PI films. This paper reports the effects of the mechanical properties of PI films exposed to an alkali (KOH) solution with different treatment time. The mechanical properties of the re-cycloimidization PI films were improved when the proper initial KOH treatment time was used. The reason might be that PI could effectively reduce the formation of the shear zone to cracks due to the increase in ductility after the proper KOH treatment and more ductile PI chains led to re-orientation at the drawing process. Therefore, the strength and elongation of the re-cycloimidization PI films were better than those of the pristine PI films. This study focused on the effects of the KOH treatment on the mechanical properties of the PI film for the first time and proposed a mechanism to explain the reason that the appropriate time of KOH treatment can enhance the mechanical properties. The results presented here can provide guidelines for preparing composite PI films via ion-exchange by the proper KOH treatment time in future studies.

Dielectric properties of sandwich-structured BaTiO3/polyimide hybrid films

In this paper, sandwich structured polyimide hybrid films were prepared by layered coating, in which middle layer is different volume fraction BT/PI monolayer film and both the bottom and the top layers are pure PI. Compared with monolayer hybrid films, sandwich structured hybrid films exert much lower dielectric loss and conductivity, which owe to pure PI layers as insulation layers effective block off conductive paths of middle layer. Besides, the SEM images show hybrid film has obvious layering and without defects. This sandwich structure can redistribute electric field between three layers to optimize breakdown performance, which correspond to data processed by Weibull breakdown distribution. When the intermediary volume fraction is 3 vol%, the breakdown strength of sandwich structured hybrid films is 344.26 kV/mm, which is 1.26 times enhancement than pure PI film. In addition, based on the improvement of the breakdown strength, the energy storage density of hybrid films is improved significantly. When the electric field is 344.26 kV/mm, its energy storage density reached 1.94 J/cm3, which is 1.72 times enhancement of pure PI film.

Mechanical, electrical and carbonization properties of graphene oxide/polyimide composite films prepared by pre-in situ polymerization

In this study, we have proposed a rather simple approach to achieving graphene oxide/polyimide (GO/PI) composite films using pre-in situ polymerization. The mechanical, electrical, and carbonization properties of the films were significantly enhanced in the presence of GO. With an addition of 1.0 wt% GO, the tensile strength and Young’s modulus were dramatically increased by 103 and 230% respectively when compared with pure PI film. Besides that, composite films show excellent electrical insulative. Especially, the GO/PI film with 1.0 wt% of GO possesses a high carbonization yield about 64.2% (1000 °C). According to the excellent performance, this approach is believed to afford broad application potential in GO–polymer composite materials.

Photo-Induced Vertical Alignment of Liquid Crystals via In Situ Polymerization Initiated by Polyimide Containing Benzophenone.

Vertical alignment of liquid crystal (LC) was achieved in an easy and effective way: in situ photopolymerization of dodecyl acrylate (DA) monomers initiated by polyimide based on 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 3,3′-dimethyl-4,4′-diaminodiphenyl methane (BTDA-DMMDA PI). The alignment behavior and alignment stabilities were characterized by a polarizing optical microscope (POM), which showed a stable vertical alignment after 12 h of thermal treatment. The chemical structures, morphology, and water contact angles of alignment films peeled from LC cells with and without DA monomers were analyzed by means of a Fourier transform infrared spectrometer (FTIR), a scanning electron microscope (SEM), and a contact angle tester, separately. The results confirmed that the DA monomers underwent self-polymerization and grafting polymerization initiated by the BTDA-DMMDA PI under ultraviolet irradiation, which aggregated on the surfaces of PI films. The water contact angles of the alignment films were about 15° higher, indicating a relative lower surface energy. In conclusion, the vertical alignment of LC was introduced by the low surface free energy of PI films grafted with DA polymer and intermolecular interactions between LC and DA polymers.