Neat Polyimide Research Articles

Mechanically strong and thermally insulating polyimide aerogels by homogeneity reinforcement of electrospun nanofibers

High-performance thermal insulating materials are greatly needed in many areas. Polyimide aerogels by freeze-drying method have shown great potential as thermal insulating materials. Improving the mechanical performance of polyimide aerogels, meanwhile without deteriorating their thermal insulating performance, is very significative. In this work, a significant homogeneity reinforcement of polyimide aerogels has been achieved by using electrospun polyimide nanofibers as the reinforcing fillers. Short nanofibers could improve strength and toughness of polyimide aerogels by dispersing stress along the pore wall and nanofibers via mechanical interlocking effect due to the good compatibility between them. Consequently, the nanofiber-reinforced polyimide (NRPI) aerogels exhibit better structural formability and excellent mechanical performance, showing compressive modulus of 3.7 MPa with a density of 54.4 mg cm−3, nearly twice that of neat polyimide aerogel. More importantly, owing to the high porosity and intertwined three-dimensional network, NRPI aerogels exhibit better thermal insulating properties compared with commercial insulating materials, especially at high temperatures. Therefore, the nanofiber reinforced polyimide aerogels with good mechanical performance are promising candidates for thermal insulating applications.

Octahedral oligomeric silsesquioxane (OAPS and OG) - Polyimide hybrid nanocomposite films: Thermo-mechanical, dielectric and morphology properties

The nano-sized SQS based polyimides have been successfully synthesized with different oxide groups such as phosphineoxide, sulfone and siloxane as in the backbone of polymer. The SQS-Polyimide nanocomposites prepared through the condensation process using amine and epoxy functionalized SQS as precursor. The presence of SQS in the resulting polyimide nanocomposites was confirmed by FTIR and XRD analyses. The presence of SQS and greatly enhances the char yield to an extent of 16% when compared to that of neat polyimide. The incorporation of SQS into polyimide lowered the value of dielectric constant from 3.31 to 2.09 at 1 MHz and the value of thermal expansion coefficient from 56.6 to 42.7 ppm/K. The composites sample prepared using 20 wt% SQS possess the lowest value of dielectric constant and CTE value. The hydrophobic nature of SQS contributes to lower the water uptake of composites from a value of 2.76 (neat polyimide) to 2.42 for POS-PI containing 20 wt% SQS. Further, the SQS polyimide composite systems possess the enhanced values of thermal stability and glass transition temperatures according their percentage weight. Data obtained from different studies, it is suggested that these hybrid composites can be used as an effective insulation materials for high performance microelectronics applications.

The effect of thermally developed SiC@SiO2 core-shell structured nanoparticles on the mechanical, thermal and UV-shielding properties of polyimide composites

SiC@SiO2 core-shell nanostructured particles were successfully prepared via simple thermal treatment. The structure of the surfaces of pristine SiC and SiC@SiO2 core-shell nanostructured particles was investigated by X-ray diffraction spectroscopy (XRD). The formation of SiO2 shell on the SiC core was further evaluated by FTIR, SEM, XPS and TEM techniques. The nanostructured particles prepared were amino-modified by APTMS and incorporated in polyimide (PI) matrix to prepare highly flexible composite films. The mechanical, thermal, UV-shielding and water proof properties of the composites were investigated. The TGA results displayed that T5 (5% weight loss temperature) and T10 (10% weight loss temperature) were meaningfully enhanced up to 56.0 °C and 53.4 °C, respectively upon adding various amounts of modified SiC@SiO2 nanoparticles into the PI matrix. DSC results revealed that the glass transition temperature (Tg) was considerably enhanced up to 45.50 °C, up on the incorporation of different dosages of SiC@SiO2–NH2 nanoparticles in the matrix. The tensile results shown that introduction of the nanoparticles into the PI medium exhibited highly significant improvement in the tensile strength and the Young's modulus over 77.1% and 96.6% respectively as compared to the neat PI. The incorporation of SiC@SiO2–NH2 nanostructured particles in the matrix highly improved the hydrophobicity of the composites up to 62.55% as compared to the neat PI. The UV-shielding properties were also enhanced when functionalized SiC@SiO2–NH2 was added to the PI matrix. The dispersion of SiC@SiO2 in the PI matrix was investigated by Scanning electron microscope (SEM).

Improved tribological properties of polyimide composites by micro–nano reinforcement

ABSTRACTThe hydroxylate carbon nanotubes (CNTs) were grafted by chemical method on the surface of the oxidized carbon fibers (CF) to improve the mechanical and tribological properties of polyimide (PI). The microstructure and fracture surface of the polyimide composites indicated that CF–CNTs hybrid as a multiscale reinforcement can distribute into the PI matrix homogeneously. Tribo‐tests further showed that CF–CNTs hybrid had a better effect on hardness increment, impact strength enhancement, friction reduction, and wear resistance. Compared to the neat PI, the friction coefficient and wear rate of CF–CNTs/PI composite deceased by 23.2 and 55.9%, respectively. In particular, the loading capacity and high speed resistance of CF–CNTs/PI composite were greatly improved. The corresponding wear mechanisms were also discussed by observing the worn surface of the PI composites. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47900.

Inhibition of Polyimide Photodegradation by Incorporation of Titanate Nanotubes into a Composite

The effect of UV light exposure on the properties of hexafluoroisopropylidene-diphthalic anhydride–oxydianiline (6FDA–ODA) polyimide (PI) and polyimide–titanate nanotube (TiNT/PI) composites has been studied using Raman spectroscopy, optical microscopy, nanoidentation and TEM. The degree of polymer photodegradation was estimated by measuring the change in affinity to a positively charged dye (methylene blue, MB). The mechanism of photoassisted transformations in polyimides usually involves scission of polymer chains accompanied by appearance of active radicals, which undergo further rapid transformations to more stable phenol, amine, and carboxylic functional groups. The accumulation of these groups can increase the degree of adsorption of charged dyes in the photodegraded polymer. It was found that neat PI showed a significantly increased capacity to adsorb MB after irradiation with UV, reaching a plateau after 1 h. In contrast, TiNT/PI composite demonstrated a much slower rise in concentration of adsorbed MB even after 4 h of UV exposure. Raman spectra indicated cleavage of C=O and C–F bonds in PI while only the C–F bond was damaged in TiNT/PI. Shorter cracks (≈ 40 µm long) appeared in TiNT/PI composites whereas macro cracks (> 100 µm) were visible in neat PI after 3 h of UV exposure. Brittleness was studied by comparing plasticity index which varied from 0 to 1 (0 corresponding to the most brittle material and 1 the most ductile one). Plasticity index reduced by 51% and 2% for PI and TiNT/PI, respectively after 3 h UV irradiation, indicating that TiNT can protect underlying PI from further damage. The hardness of neat PI decreased whereas, for TiNT/PI, it increased under UV, suggesting crosslinking of broken polymer chains with nanotubes.Graphical Photodegradation of a titanate nanotubes/polyimide composite can lead to cross-linking of broken polymer chains by nanostructured material, resulting in increased hardness.

Structural and dielectric properties of POSS reinforced polyimide nanocomposites

In this study, a series of [3-(2-aminoethyl)amino]propyl-heptaisobutyl substituted polyhedral oligomeric silsesquioxane (AHIP) containing polyimide (PI) nanocomposites were successfully prepared. Structural, thermal and electrical properties of the polyimide nanocomposites were studied. The properties of AHIP containing polyimides were compared with those of the neat polyimide films. The surface morphology of the prepared AHIP containing polyimides were determined by using Scanning Electron Microscopy (SEM). The hydrophilic/hydrophobic nature of AHIP/polyimide composites were analyzed by measuring their water contact angles. It was found that the addition of AHIP into the polyimide slightly increased the contact angle values. The incorporation of 5% AHIP to the PI matrix decreased the dielectric constant value of pure PI from 8.6 to 11.7, respectively. Furthermore he dielectric permittivity was changed from 8.6 (neat polyimide) to 5.5 (PI3).

Dielectric and Resistive Heating of Polymeric Media: Toward Remote Thermal Activation of Stimuli-Responsive Soft Materials.

Stimuli-responsive soft materials are becoming increasingly important in a wide range of contemporary technologies, and methods by which to promote thermal stimulation remotely are of considerable interest for controllable device deployment, particularly in inaccessible environments such as outer space. Until now, remote thermal stimulation of responsive polymers has relied extensively on the use of nanocomposites wherein embedded nanoparticles/structures are selectively targeted for heating purposes. In this study, an alternative remote-heating mechanism demonstrates that the dielectric and resistive thermal losses introduced upon application of an alternating current generate sufficient heat to raise the temperature of a neat polyimide by over 70°C within ≈10s. Thermal imaging is used here to measure current-induced temperature changes of polymeric media, and a proposed analytical model yields predictions that compare reasonably well with experimental data, confirming that such remote heating is viable. Conditions permitting a shape-memory polymer possessing a melting transition and susceptible to dielectric actuation to achieve continuous electrostrain-temperature cycling are identified.

Moisture absorption and hydrothermal aging of phenylethynyl-terminated pyromellitic dianhydride-type asymmetric polyimide and composites

The effects of moisture on a polymerized monomeric reactant (PMR)-type polyimide (TriA X) and associated composites were investigated. Water uptake tests were performed on the polyimide at various temperatures and relative humidity levels to investigate moisture absorption behavior. Two-stage moisture absorption was observed, in which the first stage was diffusion controlled, whereas the second stage was moisture plasticization controlled. As exposure temperature increased, the equilibrium moisture content of the polyimide decreased, indicating an exothermic absorption process. The Arrhenius temperature dependence and moisture saturation as functions of temperature and humidity in the neat polymer were determined using curve fitting based on the published mathematical models. Long-term hydrothermal aging at 95°C was conducted on the neat polyimide and associated carbon fiber composites. Reversible hydrolytic reactions and a trace of irreversible hydrolysis were observed in the long-term exposure. The tensile ductility of the neat polyimide and the short-beam shear strength of the composites decreased with increasing aging time, while the tensile strength and modulus and thermal properties of the polyimide exhibited little change after 2000-h aging, demonstrating hydrothermal stability. The decrease in the ductility of the neat polymer after long-term moisture exposure was attributed to the network structure change, driven by hydrolysis and moisture plasticization.

Multifunctional behavior of POSS-reinforced imidazole core polyimide nanocomposites

A new imidazole core unsymmetrical diamine monomer (4, 4′ (4, 5-diphenyl-1H-imidazol-1, 2-diyl) dianiline) was successfully synthesized and used as precursor to develop polyimide (PI). In addition, different weight percentages of octaaminophenyl silsesquioxane (NH2-POSS) were reinforced to form, respective, POSS–PI nanocomposites. The formation of polyimides and composites was confirmed by various spectral analyses in addition to their morphology studies by scanning electron microscopy and high-resolution transmission electron microscope. Further, the developed neat PI and POSS–PI nanocomposites were studied for their thermal, optical, dielectric and antimicrobial properties. Data resulted from different studies indicated that the incorporation of 10 wt% NH2-POSS into the PI matrix show higher glass transition temperature, higher thermal stability and better UV shielding behavior when compared to the neat PI matrix as well as other POSS–PI composites. Dielectric studies infer that the value of dielectric constant was decreased with increasing the weight percentages of NH2-POSS reinforcement and the lowest value of dielectric constant (k = 2.1) was obtained for 10 wt% POSS–PI hybrid nanocomposites in addition to its better antimicrobial behavior. Thus, the current study promises that the developed PI and POSS–PI can be used as a multifunctional composite in various high-performance applications.

High-performance polyimide nanocomposites with polydopamine-coated copper nanoparticles and nanowires for electronic applications

A multilayer-structured polyimide nanocomposite based on a combination of polydopamine (PDA)-coated copper nanoparticles (CuNPs@PDA) and copper nanowires (CuNWs@PDA) was synthesized using a flexible and rapid method. The maximum thermal conductivity of (CuNPs-CuNWs)@PDA/polyimide (PI) composite with 10 wt% filler loading was increased to 4.13 W/mK, which was an enhancement by nearly 23 times compared with the use of neat PI matrix. The relative permittivity and dielectric loss were about 4.58 and 0.022 at 1 MHz, respectively. The use of multilayer-structure facilitated increased thermal conductivity and reduced permittivity of the nanocomposite compared with CuNPs@PDA/PI and CuNWs@PDA/PI films. The highly thermal conductive nanocomposites are promising for applications in thermal management.

Formation of unique three-dimensional interpenetrating network structure with a ternary composite

Ternary composite of reduced graphene oxide/multi-walled carbon nanotubes (RGO/MWCNT)/polyimide (PI) with high-performance mechanical and electrical properties was synthesized via in situ polymerization. The unique three-dimensional interpenetrating network structure conferred the conductive pathways for electrons, resulting from the strong interfacial covalent bonds between RGO/MWCNT and the PI matrix. The electrical conductivity of (RGO/MWCNT)/PI reached 4.4 × 10− 4 S m−1 with the filler loading concentration at an extremely low value (0.2 wt%), which was significantly higher than that of the neat PI. The (RGO/MWCNT)/PI composite films exhibited high tensile strength (up to 462 MPa) and tensile modulus (260 MPa). Furthermore, the introduction of RGO/MWCNT enhanced the thermal stability of the (RGO/MWCNT)/PI composites (from 579 to 623 °C). The composite film is expected to be extensively applied in the field of electronics, solar cells and biosensors.

Improvement of mechanical, thermal and tribological properties of (3-aminopropyl) triethoxysilane-modified graphene/polyimide nanocomposites by in situ polymerisation

ABSTRACTTo elucidate the improvement and the principle of graphene modification on the polyimide (PI), (3-aminopropyl) triethoxysilane-modified graphene (PMG), was designed and prepared by anchoring the (3-aminopropyl) triethoxysilane (APTS) chain on the graphene sheet surface, and used to synthesise PI composites by in situ polymerisation. The unique surface modification significantly improved the compatibility and dispersion of graphene in the PI matrix. Tensile strength and Young’s modulus of 1.0PMG/PI was 109.45 MPa and 1.73 GPa, which increased by 54.26 and 86.02% from neat PI, respectively. The tribological properties and mechanism were also discussed. The friction coefficient and wear rate of 1.0PMG/PI (0.287, 2.291×10−5mm3 Nm−1) decreased by 47.53% and 35.06%, respectively. This improvement of the tribological properties was mainly caused by the cooperative interaction of the improved mechanical and thermal properties of the composites and the high self-lubricity of modified graphene.

Noncovalent Functionalized Graphene-Filled Polyimides with Improved Thermal, Mechanical, and Wear Resistance Properties

A facile method is proposed to prepare poly-o-phenylenediamine (PoPD) noncovalent functionalized graphene (G)-reinforced polyimide (PI) nanocomposites. PoPD-G exhibited excellent dispersibility in various organic solvents. The structures of PoPD-G were characterized by Raman and UV spectrum, which verified the π–π interactions between PoPD and G. The effective exfoliation of graphene nanosheets was investigated by observation of the morphology of PoPD-G with SEM, SPM, and TEM. Compared to PI/G composites, the interfacial adhesion between graphene nanosheets and PI matrices promoted efficient stress transfer from PI chains to PoPD-G nanofillers. Polyimide nanocomposites with different incorporations of PoPD-G exhibited outstanding thermal properties. It is interesting to note that only 0.5 wt% PoPD-G-reinforced PI composites increased by 20.8% in hardness, enhanced by 84.0% in storage modulus, and reduced by 72.8% in wear rate compared with neat PI. The eminent enhancement was attributed to the facile dispersion of graphene nanosheets and strong interface adhesion between PI and PoPD-G.

Synthesis and properties of polyimide nanocomposite containing dopamine-modified graphene oxide

Polyimide (PI)/graphene oxide (GO) nanocomposites with different loads of polydopamine-modified graphene oxide (PI/PDA-GO) were prepared. Meanwhile, the as-prepared PI/PDA-GO nanocomposites were compared with pure PI in terms of their morphologies, thermal and mechanical properties. Only a minor mass fraction of PDA-GO was required to enhance the mechanical and thermal properties of PI. The tensile strength of 1 wt% PDA-GO/PI was increased by 12% and the tensile modulus of 1 wt% PDA-GO/PI nanocomposites was increased by 25% compared to those of pure PI. Vickers hardness of the PI hybrid films increased with PDA-GO load and the maximum enhancement in Vickers hardness was observed at 2 wt% PDA-GO loading. On the other hand, the storage modulus of 1 wt% PDA-GO/PI was increased by 54% than that of neat PI. In consideration of the facile preparation of PDA-coated GO, superior physical properties over neat PI, PI/PDA-GO nanocomposites showed promising applications as functional films or composites.

Synthesis and characterization of flexible/stretchable polyimide having long/bulky aryl pendent group and polyimide/silicon dioxide nanocomposites.

A new diamine monomer having ether and azomethine linkages in the long pendent group was synthesized. New polyimide was prepared by reacting the new diamine with BTDA and nanocomposites were prepared with silicon dioxide as nanofiller. SEM analysis shows a uniform distribution of the nanopowder in the polyimide matrix. TGA shows that the polyimide and nanocomposites have good thermal stability with the T10% values varying between 440 and 458°C. DSC analysis shows Tg values between 210 and 230°C. The neat polyimide shows high elongation at break and stretchability (260%) but low tensile strength. The nanocomposites of polyimide show lower elongation at break but have improved tensile strength. The chemically imidised polyimide shows good solubility in solvents like N, N‐dimethyl formamide, N, N‐dimethyl acetamide, and N‐methyl 2‐pyrrollidone. POLYM. COMPOS., 40:832–843, 2019. © 2018 Society of Plastics Engineers

Enhanced Thermal Conductivity of Polyimide Composites with Boron Nitride Nanosheets

A strategy was reported to prepare boron nitride nanosheets (BNNSs) by a molten hydroxide assisted liquid exfoliation from hexagonal boron nitride (h-BN) powder. BNNSs with an average thickness of 3 nm were obtained by a facile, low-cost, and scalable exfoliation method. Highly thermally conductive polyimide (PI) composite films with BNNSs filler were prepared by solution-casting process. The in-plane thermal conductivity of PI composite films with 7 wt% BNNSs is up to 2.95 W/mK, which increased by 1,080% compared to the neat PI. In contrast, the out-of plane thermal conductivity of the composites is 0.44 W/mK, with an increase by only 76%. The high anisotropy of thermal conductivity was verified to be due to the high alignment of the BNNSs. The PI/BNNSs composite films are attractive for the thermal management applications in the field of next-generation electronic devices.

Effect of trace diphenyl phosphate on mechanical and thermal performance of polyimide composite films

Abstract How to achieve polyimide (PI) with better thermal and mechanical properties is a great challenge. In this study, flame-retardant diphenyl phosphate (DPhP), was incorporated in to heterocyclic diamine contained PI films to form phosphorus-polyimide composite films (P-PIs). The structures, element distribution, thermal and mechanical properties of P-PIs were characterized by FT-IR, SEM, EDS, DMA, TGA, and tensile test. The results indicated that the incorporation of phosphorus can significantly enhance the thermal and mechanical properties. The 5% weight loss temperature in air and the glass transition temperature ( Tg) of P0.6-PI film were 577 and 405 °C, which were 50 and 16 °C larger than the neat PI film, respectively. In addition, the P0.6-PI film also showed improved tensile strength , modulus and toughness by 47%, 57% and 76%, respectively, as compared to the neat PI film.

Thermomechanical Behavior of Polymer Composites Based on Edge-Selectively Functionalized Graphene Nanosheets.

In this study, we demonstrate an effective approach based on a simple processing method to improve the thermomechanical properties of graphene polymer composites (GPCs). Edge-selectively functionalized graphene (EFG) was successfully obtained through simple ball milling of natural graphite in the presence of dry ice, which acted as the source of carboxyl functional groups that were attached to the peripheral basal plane of graphene. The resultant EFG is highly dispersible in various organic solvents and contributes to improving their physical properties because of its unique characteristics. Pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) were used as monomers for constructing the polyimide (PI) backbone, after which PI/EFG composites were prepared by in situ polymerization. A stepwise thermal imidization method was used to prepare the PI films for comparison purposes. The PI/EFG composite films were found to exhibit reinforced thermal and thermo-mechanical properties compared to neat PI owing to the interaction between the EFG and PI matrix.

Durability, anti-corrosion and self-clean in air/oil of a transparent superhydrophobic polyimide film

Superhydrophobic polymeric materials have received great attention for their flexibility, anti-corrosive and self-cleaning properties. However, superhydrophobicity of ordinary polymers is likely to fail to maintain when they are exposed to a condition of high temperature. Moreover, superhydrophobic materials will lose their self-cleaning property after oil contamination or under oil. Here, we report a transparent superhydrophobic polyimide (PI) film with excellent thermal stability of superhydrophobicity and self-cleaning property after oil contamination using a fluoro- and inorganic-element free approach. Nanoscale poly(divinylbezene) (PDVB) was introduced onto PI film through a one-step solvothermal method. The PDVB@PI film shows comparable transmittance to neat PI film. PDVB@PI film shows excellent self-cleaning property under oil or oil contamination. Moreover, after being heated at 250°C, immersed in liquid nitrogen or UV-irradiation, the film is still superhydrophobic and displays similar water contact angles (WCAs) and rolling angles (RAs) at wide pH region (from 1 to 13) to the untreated PDVB@PI film. PDVB@PI film can keep its optical morphology after the corrosion of 10M NaOH for 5h, while the neat PI film is fully damaged. Its superhydrophobicity will not be lost after fire burning process. Therefore, the PDVB@PI film not only satisfies real-life requirements but also has great potential applications in many aspects.

Enhanced outcoupling in flexible organic light-emitting diodes on scattering polyimide substrates

Abstract We demonstrate an upscalable approach to increase outcoupling in organic light-emitting diodes (OLEDs) fabricated on flexible substrates. The outcoupling enhancement is enabled by introducing a thin film of microporous polyimide on the backside of silver nanowire (AgNW) electrodes embedded in neat colorless polyimide. This porous polyimide film, prepared by immersion precipitation, utilizes a large index contrast between the polyimide host and randomly distributed air voids, resulting in broadband haze (>75%). In addition, the composite polyimide/AgNW scattering substrate inherits the high thermal (>360 °C), chemical, and mechanical stability of polyimides. The outcoupling efficiency of the composite scattering substrate is studied via optical characterization of the composite substrate and electron microscopy of the scattering film. The flexible scattering substrates compared to glass/indium tin oxide (ITO) allows for a 74% enhancement in external quantum efficiency (EQE) for a phosphorescent green OLED, and 68% EQE enhancement for a phosphorescent white OLED. The outcoupling enhancement remains unharmed after 5000 bending cycles at a 2 mm bending radius. Moreover, the color uniformity over viewing angles is improved, an important feature for lighting applications.