Flexible Polyimide Films Research Articles

MULTICHANNEL PLANAR MICROELECTRODE ARRAY FOR SOMATIC MAPPING IN RATS

Planar electrode array is an important tool to evaluate perceptual or cognitive functions of the cortex and prosthetic applications. Many construction methods have been developed. To maximize the usefulness of an array electrode, a low-cost, precise, and flexible microelectrode array with low man power and short construction duration is crucial. In this study, we introduced an 8 × 8 microelectrode array on a flexible polyimide film through microelectronics fabrication. The array dimension was capable of covering the primary somatosensory cortex of a rat. The microelectrode array was insulated with biocompatible Parylene-C except of microelectrode tip. Each electrode tip was 66 μm height and separated with 0.5 mm to refine a detail somatic sensory processing. In pentobarbital anesthetized rats, stable spontaneous brain activity was successfully recorded through the electrode array. In addition, positive peaks of somatosensory evoked potentials (SEPs) elicited by stimulating rat's whisker pad, forepaw, hindpaw, and tail were obviously and consistently recorded. Latencies of SEPs increased as caudal part of the body was stimulated. The SEPs from stimulation of 4 body parts revealed different spatiotemporal patterns, which indicated a somatotopic organization of the rat. Our results demonstrated the superiority of the planar microelectrode array on the application of simultaneous recording and analysis of the brain activity in rats.

Silver nanoplates as inkjet ink particles for metallization at a low baking temperature of 100 °C

Conductive patterns on a flexible polyimide film using Ag nanoplate ink of 10 wt% solid content were successfully fabricated by inkjet printing and baking at a low temperature of 100 °C. Sintering on these printed nanoplates at a low temperature (100 °C) led to the formation of connections between nanoplates. A four-point probe measurement indicated that the resistivity of the line obtained by printing nanoplates is 26.3 μΩ-cm and this is lower than that of the line obtained by printing spherical nanoparticles, 4.3 × 10 5 μΩ-cm.

The use of aluminium doped ZnO as transparent conductive oxide for CdS/CdTe solar cells

CdTe/CdS and CdTe/ZnO thin film solar cells were grown with a high vacuum evaporation based low temperature process (≤ 420 °C). Aluminium doped zinc oxide (AZO) was used as transparent conducting oxide (TCO) material. AZO exhibited excellent stability during the solar cell processing, and no significant change in electrical conductivity or transparency was observed. The current density loss due to absorption in the 1 μm thick AZO layer with 5 Ω per square sheet resistance was found to be 1.2 mA/cm 2. We investigated the influence of an intrinsic ZnO layer (i:ZnO) in combination with various CdS thicknesses. The i:ZnO layer was found to significantly increase the open circuit voltage of the solar cells with very thin CdS layer. Increasing thickness of the i:ZnO layer leads to UV absorption losses, narrowing of the depletion layer width and hence reduced collection efficiency in the long wavelength (685–830 nm) part. With AZO/i:ZnO bi-layer TCO we could achieve cell efficiencies of 15.6% on glass and 12.4% on the flexible polyimide film.

Optical Transparency and Light Colour of Highly Soluble Fluorinated Polyimides Derived from a Novel Pyridine-Containing Diamine m, p-3FPAPP and Various Aromatic Dianhydrides

A novel pyridine-containing aromatic diamine monomer, 4-(4-trifluoromethylphenyl)-2,6-bis[3-(4-aminophenoxy)phenyl]pyridine (m,p-3FPAPP), was successfully synthesized by a modified Chichibabin reaction of 4-trifluoromethylbenzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)acetophenone (m,p-NPAP), followed by a reduction of the resulting dinitro compound 4-(4-trifluoromethylphenyl)-2,6bis[3-(4-nitrophenoxy)phenyl] pyridine (m,p-3FPNPP) with Pd/C and hydrazine monohydrate. The aromatic diamine was employed to synthesize a series of pyridine-containing polyimides by polycondensation with various aromatic dianhydrides in N,N-dimethylformamide (DMF) via the conventional two-step method, and further thermal or chemical imidization forming polyimides. The inherent viscosities of the resulting poly(amic acid)s and polyimides were 0.62–0.89 and 0.58–0.69 dl/g, and most of the polyimides obtained by chemical imidization were readily soluble in common organic solvents such as DMF, N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP) and tetrahydrofuran (THF). Meanwhile, strong and flexible polyimide films were obtained, which had good thermal stability, with a glass transition temperature (T g) of 234.4–246.6°C and the temperature at 10% weight loss of 561.4–600.6°C in nitrogen atmosphere, and good optical transparency with the cut-off wavelengths of 369–378 nm, as well as outstanding mechanical properties with tensile strengths of 89.5–96.4 MPa, a tensile modulus of 1.52–1.63 GPa and elongation-at-break of 7.2–8.7%. The polyimide films also were found to possess low water uptake (0.61–0.79%).

Thickness effect of sputtered ZnO seed layer on the fabrication of ZnO nanorods on flexible polyimide films and their ethanol gas sensing properties

ABSTRACTControlled ZnO nanostructures were grown on a flexible substrate for the future development of smart sensing tags. Thermolysis-assisted chemical solution deposition was used to grow ZnO nanorods at 85°C from 0.01mol of Zinc nitrate hexahydrate and HMT (Hexamethyltetramine) solution. To promote and modulate the ZnO nanorods, R.F. sputtered ZnO seed layers were deposited on polyimide substrates at various film thicknesses in the range of 8 to 160 nm. The optimum processing conditions to fabricate ZnO nanostructures have been investigated to examine the growth behaviors and to correlate the process parameters with the morphological characteristics. When the ethanol gas sensitivities were measured at different thickness of ZnO seed layers before growing ZnO nanorods, the highest sensitivity was obtained at 40 nm thick ZnO film at 300°C where the film thickness is similar to the Debye length. When ZnO nanorods were grown on such a ZnO seed layer, the sensitivities were more heavily influenced by the ZnO nanostructures rather than the thickness of the seed layer probably due to the dominant proportion of carrier density involved with the gas absorption.

Cellular Modulation of Polymeric Device Surfaces: Promise of Adult Stem Cells for Neuro-Prosthetics

Minimizing the foreign body response is seen as one critical research strategy for implants especially when designed for immune-privileged organs like the brain. The context of this work is to improve deep brain stimulating devices used in a consistently growing spectrum of psychomotor and psychiatric diseases mainly in form of stiff electrodes. Based on the compliance match hypothesis of biocompatibility we present another step forward using flexible implant materials covered with brain cell-mimicking layers. We covered two types of flexible polyimide films with glandular stem cells derived from pancreatic acini. Using real time-PCR and fluorescent immunocytochemistry we analyzed markers representing various cell types of all three germ layers and stemness. The results demonstrate an unchanged differentiation potential of the polyimide fixated cells as measured by mRNA and protein level. Additionally we developed a fibrinous hydrogel coating to protect them against shear forces upon eventual implantation. By repeating previous analysis and additional metabolism tests for all stages we corroborate the validity of this improvement. Consequently we assume that a stem cell-containing cover may provide a native, fully and actively integrating brain-mimicking interface to the neuropil.

Monolithic and Flexible Polyimide Film Microreactors for Organic Microchemical Applications Fabricated by Laser Ablation

Immer flexibel bleiben: Ein Mikroreaktor bestehend aus flexiblem Polyimidfilm wurde entwickelt. Er ist leichter herzustellen als Glas-Mikroreaktoren und, anders als andere Polymermikroreaktoren, inert gegen Lösungsmittel und Säuren bei drastischen Bedingungen. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Novel organosoluable aromatic polyimides derived from unsymmetrical 1,3-bis(4-aminophenoxy)naphthalene and aromatic dianhydrides

A novel unsymmetrical diamine, 1,3-bis(4-aminophenoxy)naphthalene, was prepared through the nucleophilic displacement of 1,3-dihydroxynaphthalene with p-fluoronitrobenzene in the presence of potassium carbonate, followed by catalytic reduction with hydrazine. A series of novel aromatic polyimides containing bis(phenoxy)naphthalene units were synthesized from the unsymmetrical diamine and a range of aromatic tetracarboxylic dianhydrides via the usual two-step procedures that included ring-opening polyaddition and thermal/chemical cyclodehydration. The poly(amic acid)s had inherent viscosities ranging from 0.65 to 2.01 dL/g. All the poly(amic acid)s could be converted thermally into transparent, flexible, and tough polyimide films. Most of the polyimides were soluble in organic solvents, such as dimethylacetamide, N-methyl-2-pyrrolidone, m-cresol, or o-chlorophenol due to the unsymmetrical and bulky pendant naphthalene groups. The tensile strength and elongation at break of the polyimide films ranged from 74 to 97 MPa and 4 to 7%, respectively. These polyimides had glass transition temperatures ranging from 221 to 312 °C. Thermogravimetric analysis revealed these polymers to be fairly stable up to 500 °C, and the 10% weight loss temperature were recorded in the range of 531–580 °C in nitrogen and 522–570 °C in air. The substituted position effect of bis(phenoxy)naphthalene on the properties of the polyimides were investigated. The polyimides derived from unsymmetrical 1,3-substituted bis(4-aminophenoxy) naphthalene showed better solubility without sacrificing their thermal and mechanical properties due to the unsymmetrical and bulky pendant effects.

Surface modification of a flexible polyimide film using a reactive fluorinated polymer nanosheet

This paper describes an effective approach to surface modification of a flexible polyimide film using a reactive fluorinated polymer nanosheet. N-(1 H,1 H-pentadecafluorooctyl)methacrylamide copolymers containing carboxyl group as a reactive moiety form stable monolayer on the water surface and highly ordered reactive polymer nanosheets can be fabricated by the Langmuir–Blodgett technique. This reactive fluorinated polymer nanosheet was utilized to modify the surface properties of polyimide film through its immobilization using thermal treatment. The modification process was studied by X-ray photoelectron spectroscopy (XPS) and modified PI surface was characterized by contact angle measurements and atomic force microscopy (AFM).

Effect of CF 4 plasma treatment on the interfacial fracture energy between inkjet-printed Ag and flexible polyimide films

The effects of a CF 4 plasma treatment on the interfacial fracture energy of an inkjet-printed Ag/polyimide system were investigated for inkjet printing metallization techniques in flexible printed circuit board applications. The interfacial fracture energy was evaluated by using a 180° peel test and by calculating the plastic deformation energy of the peeled metal and polyimide films from an energy balance relationship during the steady-state peeling process. The interfacial fracture energy between the Ag and the polyimide increased after the CF 4 plasma treatment to the polyimide surface. This was caused by an increase in the surface roughness as well as changes to the surface functional groups of the polyimide film. Therefore, both the mechanical interlocking effect and the chemical bonding effect were responsible for the improvement in the interfacial adhesion in inkjet-printed Ag/polyimide systems.

Inside Cover: Monolithic and Flexible Polyimide Film Microreactors for Organic Microchemical Applications Fabricated by Laser Ablation (Angew. Chem. Int. Ed. 39/2010)

Inside Cover: Monolithic and Flexible Polyimide Film Microreactors for Organic Microchemical Applications Fabricated by Laser Ablation (Angew. Chem. Int. Ed. 39/2010)

Monolithic and Flexible Polyimide Film Microreactors for Organic Microchemical Applications Fabricated by Laser Ablation

Glass, silicon, poly(dimethylsil-oxane) (PDMS), and poly(methylmethacrylate) (PMMA)have been used for the fabrication of miniaturized devices.Fabrication with glass or silicon substrates requires relativelycomplex processes, and the fabrication costs are high.Relatively cheap polymers such as PDMS or PMMA arenot suitable for application in organic chemical processesowing to their low chemical stability and easy swelling.

Wafer-Scale Fabrication of Single Polypyrrole Nanoribbon-Based Ammonia Sensor

Ultra-long (>1 cm) polypyrrole (PPy) nanoribbons were batch-synthesized to predetermined locations on 4 inch Si wafers and flexible polyimide film with controlled thicknesses and widths via modified Lithographically Patterned Nanowire Electrodeposition (LPNE), which combines top-down “photolithography” and bottom-up “electrodeposition”. The excessive lengths and lithographic approach enable subsequent patterning of electrodes for direct device fabrication. Electrical transport properties were investigated by temperature-dependent measurements, and back-gated FET measurements were performed to study the properties with respect to the conductivity of PPy nanoribbons. To demonstrate the utility of this approach these nanoribbon devices were interrogated as gas sensors in a conductometric fashion. They displayed excellent sensitivity toward ammonia vapor with a detection limit in the sub ppm. The sensitivity toward ammonia vapor was tuned by the conductivity of the PPy nanoribbons via chemical de/doping.

Organic thin film transistors on flexible polyimide substrates fabricated by full-wafer stencil lithography

This paper presents new results on miniaturized pentacene thin film transistors (TFTs) fabricated on a spin coated polyimide (PI) film. Patterning steps, which are vital for the integrity and electrical performance of organic TFTs, were done using resistless shadow-mask lithography with two high precision MEMS fabricated stencils, thus avoiding solvents and high temperature processes. Both pentacene and source–drain (S/D) electrodes were directly patterned through stencils with high accuracy on wafer scale. The TFTs have been characterized before and after peeling the flexible PI film off the rigid surface, showing full transistor functionality in both cases.

Characterizations and thermal stability of soluble polyimide derived from novel unsymmetrical diamine monomers

Two kinds of novel aromatic, unsymmetrical diamines with ether–ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 3-amino-4′-(4-aminophenoxy)-benzophenone, was successfully synthesized by two different synthetical routes and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride, via a conventional two-step thermal or chemical imidization method to produce a series of fluorinated polyimides. The polyimides were characterized with solubility tests, viscosity measurements, mechanical properties tests, IR-FT, and thermogravimetric analysis. The polyimides had inherent viscosities of 0.54–0.77 dL/g and were easily dissolved in both polar, aprotic solvents and common, low-boiling-point solvents. The resulting strong and flexible polyimide films exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 573 °C and glass-transition temperatures in the range of 222–251 °C. Moreover, the polymer films showed outstanding mechanical properties, with tensile strengths of 86.5–121.6 MPa, elongations at break of 9–16%, and initial moduli of 1.26–1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.

Flexible Temperature Sensor Array Based on a Graphite-Polydimethylsiloxane Composite

This paper presents a novel method to fabricate temperature sensor arrays by dispensing a graphite-polydimethylsiloxane composite on flexible polyimide films. The fabricated temperature sensor array has 64 sensing cells in a 4 × 4 cm2 area. The sensor array can be used as humanoid artificial skin for sensation system of robots. Interdigitated copper electrodes were patterned on the flexible polyimide substrate for determining the resistivity change of the composites subjected to ambient temperature variations. Polydimethylsiloxane was used as the matrix. Composites of different graphite volume fractions for large dynamic range from 30 °C to 110 °C have been investigated. Our experiments showed that graphite powder provided the composite high temperature sensitivity. The fabricated temperature sensor array has been tested. The detected temperature contours are in good agreement with the shapes and magnitudes of different heat sources.

Synthesis and characterization of fluorinated polyimides derived from novel unsymmetrical diamines

Two kinds of aromatic, unsymmetrical diamines with ether–ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 4-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone, were successfully synthesized with two different synthetic routes. Then, they were polymerized with 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride to form a series of fluorinated polyimides via a conventional two-step thermal or chemical imidization method. The resulting polyimides were characterized by measuring their solubility, viscosity, mechanical properties, IR-FT, and thermal analysis. The results showed that the polyimides had inherent viscosities of 0.48–0.68 dl/g and were easily dissolved in bipolarity solvents and common, low-boiling point solvents. Meanwhile, the resulting strong and flexible polyimide films exhibited excellent thermal stability, e.g., decomposition temperatures (at 10% weight loss) are above 575 °C and glass-transition temperatures in the range of 218–242 °C. The polymer films also showed outstanding mechanical properties, such as tensile strengths of 86.5–132.8 MPa, elongations at break of 8–14%, and initial moduli of 1.32–1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.

Synthesis and characterization of novel polyimides derived from 4-phenyl-2, 6-bis [3-(4-aminophenoxy)-phenyl]-pyridine diamine and aromatic dianhydrides

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2, 6-bis [3-(4-aminophenoxy)phenyl]-pyridine( m-PAPP),was synthesized by a modified Chichibabin reaction of benzaldehyde and a substituted acetophenone, 3-(4-nitrophenoxy)-acetophenone( m-NPAP), and a reduction of the resulting dinitro compound 4-phenyl-2, 6-bis[3-(4-nitrophenoxy)phenyl]-pyridine ( m-PNPP) with Pd/C and hydrazine monohydrate, successively. A series of novel aromatic polyimides were prepared from the diamine with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities of the resulting poly (amic acid) precursors were 1.37–1.56 dL/g, and these polymers could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The glass transition temperatures of these polymers were recorded at 180–264 °C. All of these novel polyimides held 10% weight loss at the temperature above 430 °C and left more than 50% residue even at 800 °C in air, as well as have outstanding mechanical properties with the tensile strengths of 91.6–114.1 MPa and elongations at breakage of 10.1–15.7%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.

Synthesis and characterization of soluble polyimides based on a new fluorinated diamine: 4-Phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine ( m-PAFP), was successfully synthesized by a modified Chichibabin reaction of 3-(4′-nitro-2′-trifluoro-methyl-phenoxy)-acetophenone with benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities values of these polyimides were in the range of 0.56–1.02 dL/g, and they could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The polyimides had good thermal stability, with the glass transition temperatures ( T g) of 187–211 °C, the temperatures at 5% weight loss of 511–532 °C, and the residue at 800 °C in air was higher than 50%. These films also had dielectric constants of 2.64–2.74 at 10 MHz and low water uptake 0.53–0.66%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous. Moreover, the polymer films of these novel polyimides showed outstanding mechanical properties with the tensile strengths of 90.1–96.6 MPa, elongations at breakage of 8.9–10.7% and tensile modulus of 1.65–1.98 GPa.

Synthesis and Characterization of Highly Refractive Polyimides Derived from Thiophene-Containing Aromatic Diamines and Aromatic Dianhydrides

Aromatic thiophene-containing diamines, 2,5-bis(4-aminophenylsulfanyl)thiophene (APST) and 2,5-bis{2′-[5′-(4′′-aminophenyl)sulfanyl]thienyl}thiophene (APSTT), were synthesized and polymerized with a sulfur-containing dianhydride, 4,4′-[p-thiobis(phenylenesulfanyl)]diphthalic anhydride (3SDEA) and 4,4′-oxydiphthalic anhydride (ODPA), respectively, to afford four poly(amic acid)s (PAAs) with inherent viscosities of 0.41 to 1.68 dL/g. Flexible and tough polyimide (PI) films obtained from the PAA precursors showed good thermal, mechanical, and optical properties. The glass-transition temperatures (Tg) of the PIs were in the range of 157−220 °C, determined by differential scanning calorimetry (DSC), and 160−216 °C by dynamic mechanical analysis (DMA), depending on the dianhydride used. The 10% weight loss temperatures were in the range of 354−456 °C, showing relatively high thermally resistant characteristics of the PI films. The PI films also showed good optical transparency above 500 nm, which agreed well wi...