Polyimide Surface Research Articles

Surface composite engineering of polyimide to create amine functionalities for autocatalytic metallization

Autocatalytic metallization of polyimide (PI) is accomplished through surface composite engineering as a facile approach to fabricate flexible printed circuit boards. The surface composite engineering of PI involves the generation of active sites by plasma activation, attachment of amine-terminated organosilanes through covalent bonding with the active sites, adsorption of a palladium catalyst by a complex reaction with the amine groups, and electroless deposition of copper through autocatalytic metallization. Three aminosilanes with various numbers of amine units are employed to silanize the PI surface and to create amine functionalities, successfully achieving a high coverage of copper deposition. The standard 90° peeling test further identifies that the aminosilane with one amine unit outperforms the others with two and three amine units in the adhesion performance of the copper layer, with the highest peel strength reaching 0.8 kgf/cm. A systematic study is performed to experimentally and theoretically explore the grafting conformation of the three aminosilane/PI composite systems at the atomic level, and the correlation with the peel strength performance is also investigated.

Surface alteration implications on potential use of semi-alicyclic polyimide as biomedical materials

A semi-alicyclic polyimide (PI) is tested for hemocompatibility and cell growth purposes. The PI configuration in the presence of the adhesion proteins and interaction energy were computed showing a different stability dictated by the protein structure. PI film surface was altered by roughening with sand paper and the morphology was examined by atomic force microscopy (AFM). The recorded images show a conversion of the initial isotropic peak-to-valley height on the surface of the PI film into an anisotropic one made of microgrooves. This is supported by the amplitude distribution function, which for the pristine sample has a narrow peak (a single morphological entity), while upon surface roughening, it has two peaks, associated with tracks valleys and top of the hills. The shape parameters (skewness and kurtosis) related to the asymmetry of the surface departure and spread of the height distribution are significantly changed after altering of the PI surface. The values of the surface functional indexes and functional volume parameters are increasing upon the PI surface roughening. The changes in random character of the initial PI are also evidenced by autocorrelation cross-section profile. The altered PI film surface determines an anisotropic character of adhesion or spreading of blood and fibroblasts.

Preparation of flexible ZnO@ZIF-8 heterojunction materials and study on photoluminescence properties

The development of flexible display materials with foldable and high luminescent properties plays an important role in modern development. With incomplete imidized polyimide (PI) film, PI as the substrate and ZnO as the self-sacrificing template, ZnO seed and ZnO@ZIF-8 nanorod were successfully prepared by sol–gel and hydrothermal methods on the surface of PI, forming a thin ZnO@ZIF-8 buffer layer. PI-ZnO@ZIF-8 with great optical performance can be obtained when the ratio of N, N-dimethylformamide (DMF): H2O is 1:1, reaction time is 4 h and temperature is 70℃,The surface defect passivation effect promotes the charge separation, the absorption wavelength increases from 350 nm to 360 nm, and ZnO@ZIF-8 effectively enhances the light capture in the visible region and the luminescence intensity at 625 nm.

A new approach for directional homogeneous alignment of liquid crystals using electric field-guided orientation of nonionic amphiphiles

Conventional homogeneous alignment of liquid crystals (LCs) utilizes rubbed or photo-aligned polyimide surfaces that determine the molecular orientation of LCs along in-plane direction. However, this alignment method based on polymeric layer requires complicated layer forming processes and considerable synthetic effort for special functional polyimides. In this study, a simple and unprecedented directional alignment approach has been developed to horizontally align nematic LCs using electric field-guided orientation of nonionic amphiphiles, spontaneously forming nanoscale supramolecular thin layer on the indium tin oxide substrate via hydrogen bonding. The in-plane electric field between simple slit electrodes induced the horizontal orientation of the anchored amphiphilic molecules parallel with electric field. Furthermore, the subsequent immobilization of inclined amphiphiles along a directional electric field through photopolymerization of common mesogenic diacrylates within LC medium resulted in a new type of homogenous alignment layer with a well-defined orientation direction for LCs. The proposed facile alignment methodology using small quantities of nonionic amphiphiles and mesogenic diacrylates afforded uniform and stable planar alignment of LC molecules with the controlled director. This novel alignment approach is expected to find a wide range of potential applications involving LC displays, optically patterned retarders, biosensors, and electronic lenses.

Scaffold-structured polymer binders for long-term cycle performance of stabilized lithium-powder electrodes

ABSTRACT Effects of soluble polyimide (PI) binders on large-sized Li anodes (width = 21.5 cm; thickness = 40 μm) prepared using Li-metal powder (LiMP) have been investigated. PI binders form a uniform protective layer on exposed Li-powder-coated surfaces, thereby resulting in formation of scaffold-structured LiMP-based anodes. Uniform PI surface films favor realization of Li plating on Li-metal surfaces by forming a smooth surface structure, and the three-dimensional insulating PI matrix functions as a buffer layer that absorbs volume change. Moreover, PI binders facilitate enhanced cohesion between LiMP particles. The above-described triple action of PI binders significantly reduces Li dendrites. Consequently, PI-containing LiMP-based metal anodes demonstrate enhanced electrochemical performance compared to both polymeric binders and bare Li-metal foils. Results obtained in this study reveal that LiMP-based anodes containing PI binders exhibit 89% (98.2 mAh g–1) discharge-capacity retention during the 200th cycle, whereas bare Li-metal foil demonstrates sudden degeneration during the 65th cycle. Furthermore, PI containing LiMP-based anodes exhibit improved rate capability compared to other polymeric binders considered in this study.

Non-thermal plasma activation of BPDA-PPD polyimide for improved cell-material interaction

Biocompatible BPA-PPD polyimide is widely used in the packaging of implantable devices. Plasma activation can improve its interaction with the surrounding tissue upon implantation. The influence of He, air, N2 and Ar plasma activation on polyimide's surface hydrophilicity, roughness, topography, composition and cell-surface interaction was evaluated, along with the influence of hydrophobic recovery on such properties. All plasma activations increased the surface hydrophilicity but neither the roughness nor topography changed. The increase was attributed to the incorporated O- and N-functionalities. 24 h after the activations the surface hydrophilicity decreased while maintaining the functionalities, due to the functionalities’ reorientation/migration towards the bulk of polyimide. Air and N2 activations improved the cell-surface interactions with fibroblasts. These were equally influenced by the surface hydrophilicity and the surface functionalities availability. The hydrophobic recovery lowered the initial cell adhesion but not the cell proliferation, as the hydrophobic recovery was progressively reversed in the culture media.

The Surface Morphology Effects on Liquid Crystal Alignment After Photo-Agitation and Crosslinking of Polyimide.

The photo-reactive activators are highly reactive radical generators upon the ultraviolet (UV) light illumination. The photo-reactive initiators produced nitrogen radical and alkyl radical after releasing carbon dioxide. The radicals could react with polyimide (PI) main chains. These reactions enforced the alignment layers and exhibited high azimuthal anchoring energy. The thickness of photo-irradiated PI alignment layers were reduced dramatically by photo-induced crosslinking, which induced surface wrinkling and roughness. The carbon dioxide gases released from the thin films produced many micro-pores, which provides tight anchoring of liquid crystal (LC) molecules. The azimuthal anchoring energy obtain by photo-alignment was better than that obtain by rubbing method with the same PI. The maximum value was 6.92×10-5 J/m². Small aliphatic hydrocarbons, such as methane and propene, were released during photo-decomposition reaction from the PI surface. The polarity of film surface became more hydrophilic. The photo-alignment of LC was perpendicular to the polarization axis of UV light. On the basis of high anchoring energy, the rough surface, hydrophilic surface, and rapid photo-reactions, the photo-alignment mechanism is proposed.

Polyimide Surface Modification Using He-H2O Atmospheric Pressure Plasma Jet-Discharge Power Effect

The atmospheric pressure He- H 2 O plasma jet has been analyzed and its effects on the Kapton polyimide surface have been investigated in terms of discharge power effect. The polyimide surfaces before and after plasma treatment were characterized using atomic force microscopy (AFM), X-ray photoelectrons spectroscopy (XPS) and contact angle. The results showed that, increasing the discharge power induces remarkable changes on the emission intensity, rotational and vibrational temperatures of He- H 2 O plasma jet. At the low discharge power ≤5.2 W, the contact angle analysis of the polyimide surface remarkably decrease owing to the abundant hydrophilic polar C=O and N–C=O groups as well as increase of surface roughness. Yet, plasma treatment at high discharge power ≥5.2 W results in a slight decrease of the surface wettability together with a reduction in the surface roughness and polar groups concentrations.

Molecular Ordering Behavior of Lyotropic Chromonic Liquid Crystals on a Polyimide Alignment Layer

Coating-type polarizing films with high dichroic ratio (DR) and polarization efficiency in the visible region were fabricated using a solution of ternary lyotropic chromonic liquid crystals (LCLCs). Optical characteristics of these anisotropic LCLC polarizing films were then determined. DR increased with increasing LCLC concentrations. Molecular ordering of these LCLCs on a rubbed polyimide (PI) layer increased because LCLC molecules' orientation was enhanced by the dielectric anisotropy effect from rubbing the surface of the PI. In addition, this study demonstrated how the interaction between liquid crystal aggregates and the PI surface with different LCLC solutions correlated with LCLC molecular orientations on the PI which significantly depended on whether the coating direction of the LCLC solution was parallel or perpendicular to the PI rubbing direction. It was found that ordering direction at high LCLC concentrations was determined by shearing direction of the LCLC solution coating whereas the ordering direction at low LCLC concentrations was governed by the dielectric anisotropy effect from PI rubbing direction.

Optical Second Harmonic Generation Analysis of Unrubbed Polyimide Surfaces as a Function of the Content of Steroidal Structure Side Chains

Optical Second Harmonic Generation Analysis of Unrubbed Polyimide Surfaces as a Function of the Content of Steroidal Structure Side Chains

Flexible Anode Catalysts for Direct Hydrazine Fuel Cells

In this study we report a facile approach for fabrication of flexible anode catalysts consisting of a fiber-shaped cobalt deposited on the polyimide (PI) surface for direct hydrazine fuel cells (DHFCs). At first, a thin copper layer has been deposited on the PI surface using electroless metal plating method. Then, the fiber-shaped cobalt coating has been plated by the electrochemical deposition method from the electrolyte containing CoSO4, NaOH and N-(2-Hydroxyethyl) ethylenediamine. For comparison, the cobalt layer that has the smooth structure has been deposited on the flexible PI surface via electroless deposition using morpholine borane as a reducing agent.The morphology and composition of the prepared flexible catalysts have been characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. The activity of catalysts has been investigated with respect to the oxidation of hydrazine in an alkaline medium.The results of electrochemical measurements showed that the deposited cobalt layer that has a fiber-shaped structure on the flexible PI surface exhibits an enhanced electrocatalytic activity towards the oxidation of hydrazine as compared with that for cobalt catalyst that has a smooth structure. Moreover, the prepared flexible catalysts seem to be a promising anode material for DHFCs.

Preparation of a SiO x coating with a lot of micro–nanometre wrinkles on the polyimide surface and its resistance to corrosion

ABSTRACT The preparation of inorganic coatings on polymer surfaces to improve their performance is a frequently used method. However, the cracking and falling off of the coatings caused by different thermal expansion coefficients or poor adhesion between the coatings and polymer substrates need to be solved. In this paper, the preparation of a SiO x coating with a lot of micro–nanometre wrinkles is proposed, using the scalability of wrinkles to alleviate or eliminate the stress. The wrinkled coating is prepared on the polyimide surface by a sol forming process. Environmental simulation tests showed that the coatings exhibit resistance to moisture and temperature change, and have a good anti-atomic oxygen performance.

Well-organized organosilane composites for adhesion enhancement of heterojunctions

Flexible copper clad laminate (FCCL) is the key base material for versatile applications such as mobile devices, wearable electronics, and point-of-care biosensors. Development of adhesiveless FCCL is urgent to achieve a thinner, lighter, and thermally stable substrate for advanced high-frequency (5G) applications. In this study, a co-silanization method is proposed to functionalize the polyimide (PI) surface for efficient metal immobilization and adhesion enhancement. The co-silanization treatment features the establishment of a barricade-like network structure by the assistant organosilane, trimethoxyphenylsilane (TMPS), to generate spatial confinement effect (SCE) to effectively control the positioning and grafting orientation of the functional organosilane, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (ETAS), on the PI film. Benefitting from the effective positioning and grafting, the two types of organosilanes form a composite well-organized molecular nanolayer which is in possession of strong tethering ability for metal attachment and immobilization. Compared to the mono-silanization system with ETAS only (0.652 kgf/cm), the co-silanization treatment (ETAS + TMPS) remarkably enhances the peel strength of the deposited metal layer on PI by 53% (~1 kgf/cm).

Effect of 172-nm UV irradiation on polyimide and its application in surface modification by grafting

Polyimides (PIs) have a wide range of industrial and scientific applications due to their excellent thermal and mechanical stability and chemical resistance. Their response to ultraviolet (UV) irradiation is of further interest in high-value applications such as spacecraft technology and electronics packaging. In this work, we investigated the effect of 172-nm UV xenon excimer lamp irradiation on samples of pyromellitimido-oxydianiline (PMDA-ODA) commercial films in the absence of oxygen. The average irradiance received at the sample position was 90 mW/cm2, and the total radiation dosage varied from 0 to 64 J/cm2. X-Ray photoelectron spectroscopy, time-of-flight-secondary ion mass spectrometry, atomic force microscopy, and contact angle measurements were used to characterize the effect. Calculated UV-visible spectroscopy absorption spectra were obtained using the ZINDO//B3LYP/3-21G method to give an indication of which orbitals are involved in the transitions near 172 nm. The reactivity of the different UV-treated PI samples toward nitrogen-borne heptafluorodecene vapor was then investigated using the above techniques. Grafting reactions occurred on the surface of the photochemically activated polymer. This study explored the potential for modification of PI surfaces using UV-light-assisted grafting to impart valuable functionalities.

Laser-induced synthesis of carbon-based electrode materials for non-enzymatic glucose detection

We report one-step synthesis of carbon-based microstructures on the surface of polyimide by using the 2D direct laser writing technique. It was shown that the properties of obtained conductive structures can be tuned by varying the conditions of the laser synthesis (scanning speed, laser power). The fabricated materials exhibited high electrochemical activity towards d-glucose measured by cyclic voltammetry analysis (limit of detection—0.564 μM and 6.31 μM for different linear ranges). Comparatively high sensing activity of the synthesized structures makes them promising materials for flexible non-enzymatic biosensing devices.

FEM Simulation of Charge Accumulation Behaviours on Polyimide Surface in 10 kV Negative High-Voltage Corona Polarization Process

The study investigates behaviors of charge accumulation on an insulated surface from micro perspective via the numerical method. A coupling bridge between the micro-ion reaction system and the macroscopic multi-physical field was constructed by means of the electronic energy distribution function, which revealed the coupling mechanism in the process of corona charge. Moreover, it revealed the transport and accumulation mechanism of charge on the surface of insulating materials. 2D axisymmetric finite element model was built based on the multi-physical field coupling theory. 10 kV negative voltage was applied using a pin-plate electrode structure and polyimide film was taken as insulated surface to simulate the dynamic charge accumulation behaviors in the corona discharge process. The generation, migration and distribution laws of charged ions and electrons in different stages of corona discharge process were given. Charge distribution laws in different stages of charge process of polyimide were given and discussed. When corona discharge reached quasi-stationary state, the total charge number accumulated on the surface was at 10 -10 Coulomb order of magnitude, and the drift current was at 10 -7 ampere order of magnitude. An experimental platform was set up to test drift current and charge distribution under quasi-stable discharge state. The results show that the simulation results and the experimental data under quasi-stable state are consistent, thus indirectly verifying the correctness of the proposed numerical simulation algorithm and its simulation results.

Hydrophilic surface-assisted thermoresponsive smart window based on lower critical solution temperature type phase separation

We investigated the effect of an atmospheric pressure plasma treatment on a thermoresponsive ionic liquid device, which exhibits lower critical solution temperature type phase separation. The opaque state for the ionic liquid device with a polyimide treated by the atmospheric pressure plasma was dramatically stabilized, because H2O microdroplets were pinned onto the polyimide. This surface-assisted stabilization originated from a hydrophilic interaction, such as hydrogen bonds between H2O droplets and various oxygen-containing functional groups at the polyimide surface, which was generated by the atmospheric pressure plasma. This unique technique is expected to develop information display devices whose function is driven by temperature.

Nature-inspired chemistry toward hierarchical superhydrophobic, antibacterial and biocompatible nanofibrous membranes for effective UV-shielding, self-cleaning and oil-water separation

Fabrication of environmental-friendly, low-cost, and free-standing superhydrophobic nanofibrous membranes with additional functionalities such as self-cleaning and UV-shielding properties is highly demanded for oil-water separation. Herein, we describe the preparation of multifunctional superhydrophobic nanofibrous membrane by using a facile and novel nature-inspired method, i.e., plant polyphenol (tannic acid) metal complex is introduced to generate rough hierarchical structures on the surface of an electrospun polyimide (PI) nanofibrous membrane, followed by modification of poly (dimethylsiloxane) (PDMS). Taking an as-prepared tannic acid − Al3+-based superhydrophobic membrane as an example, it not only exhibits anti-impact, low-adhesive and self-cleaning functions, but also presents excellent performance in the separation of various oil-water mixtures. A high flux up to 6935 l m−2 h−1 with a separation efficiency of over 99% and the oil contents in water below 5 ppm is obtained even after repeating use for twenty separation cycles. Additionally, the membrane exhibits excellent UV-shielding property, attributing to the inherent UV-absorbing ability of tannic acid. Furthermore, the membrane also possesses additional properties including antibacterial activity, good biocompatibility, robust mechanical strength, and excellent resistance to various harsh conditions. These attractive properties of the as-prepared membrane make it a promising candidate for potential applications in industrial oil-contaminated water treatments and oil-water separation.

Growth Behavior of SiO2 Films on Polyimide Substrates after Ion-Beam Treatment

This study investigated the effects on physical and chemical properties of a polyimide (PI) substrate of the exposure time and the flow rates of argon and oxygen for ion-beam treatment. The surface roughness, morphology, and chemical bonding states of the PI surface were analyzed, and the change in hydrophilicity of PI after ion-beam treatment was investigated. The contact angle of PI decreased after ion-beam treatment, which is considered to be due to increases the in surface roughness and the proportion of hydrophilic bonds such as C-O. Particularly, ion-beam treatment with argon and oxygen flow rates of 25 and 25 sccm, respectively, decreased the contact angle from 61.6° to 32.9° and increased the proportion of C-O bonds from 3.5% to 15.7%. Finally, the thin SiO2 layer which was deposited on ion-beam treated PI showed a smoother and flatter morphology than that on pristine PI due to the increase in the hydrophilicity of the PI substrate.

Imaging of triboelectric charge distribution induced in polyimide film by using optical second-harmonic generation: Electronic charge distribution and dipole alignment

By using an optical second-harmonic generation (SHG) microscope, we visualized spatial distribution of triboelectric charge in polyimide films, which are negatively charged by rubbing with a cotton belt. The origins of this triboelectric charging were excessive electronic charges and aligned dipoles. The excessive electronic charges were imaged using the probe laser wavelength of 1140 nm (SHG wavelength 570 nm), whereas the aligned dipoles were visualized by choosing the laser wavelength of 570 nm (SHG wavelength 285 nm). Combining the two visualized images showed that the dipolar alignment region with a width of 10 μm was induced on the rubbed polyimide surface, and at the same time, excess electronic charges were generated in that region. We conclude that dipolar alignment and electronic charging are main contributors, and the interaction between the two contributors plays an essential role in triboelectrification.