A water-soluble polyimide precursor: Synthesis and characterization of poly(amic acid) salt

Low-power laser manufacturing of copper tracks on 3D printed geometry using liquid polyimide coating

Silver nanoparticle photoreduction synthesis by direct laser writing is a process that enables copper micro-track production on very specific polymers. However, some important 3D printing polymers, such as acrylonitrile butadiene styrene (ABS) and acrylates, do not accept this treatment on their surface. This work presents an approach to produce copper microcircuitry on 3D substrates from these materials by using direct laser writing at low power (32 mW CW diode laser). We show that by coating a thin layer of polyimide (PI) on a 3D-printed geometry, followed by a sequence of chemical treatments and low-power laser-induced photoreduction, copper tracks can be produced using silver as catalyst. The surface chemistry of the layer through the different stages of the process is monitored by FTIR and X-ray photoelectron spectroscopy. The copper tracks are selectively grown on the laser-patterned areas by electroless copper deposition, with conductivity (1.2 ± 0.7) × 10⁷ S m^-1 and a width as small as 28 μm. The patterns can be written on 3D structures and even inside cavities. The technique is demonstrated by integrating different circuits, including a LED circuit on 3D printed photopolymer acrylate and a perovskite solar cell on an ABS 3D curved geometry.

Influence of Mixed Imide Composition and Thermal Annealing on Ionic Liquid Uptake and Conductivity of Polyimide-Poly(ethylene glycol) Segmented Block Copolymer Membranes

Understanding the impact of different bridging groups in the two-step polymerization of poly(ethylene glycol) (PEG)-incorporated polyimide (PI) materials is significant. It is known that the proton exchange membranes (PEMs) used in industry today can experience performance degradation under rising temperature conditions. Many efforts have been devoted to overcoming this problem by improving the physical and mechanical properties that extend the hygrothermal life of a PEM. This work examines the effect of oxygenated and fluorinated bridging anhydrides in the production of PI-PEG PEMs. It is shown that the dianhydride identity and the amount incorporated in the synthesis influences the properties of the segmented block copolymer (SBC) membranes, such as increased ionic liquid uptake (ILU), enhanced conductivity and higher Young's modulus favoring stiffness comparable to Nafion 115, an industrial standard. Investigations on the ionic conductivity of PI-PEG membranes were carried out to determine how thermal annealing would affect the material's performance as an ion-exchange membrane. By applying a thermal annealing process at 60 °C for one hour, the conductivities of synthesized segmented block copolymer membranes values were increased. The effect of thermal annealing on the mechanical properties was also shown for the undoped SBC via measuring the change in the Young's modulus. These higher ILU abilities and mechanical behavior changes are thought to arise from the interaction between PEG molecules and ethylammonium nitrate (EAN) ionic liquid (IL). In addition, higher interconnected routes provide a better ion-transfer environment within the membrane. It was found that the conductivity was increased by a factor of ten for undoped and a factor of two to seven for IL-doped membranes after thermal annealing.

3D Printing of Thermal Insulating Polyimide/Cellulose Nanocrystal Composite Aerogels with Low Dimensional Shrinkage

Polyimide (PI)-based aerogels have been widely applied to aviation, automobiles, and thermal insulation because of their high porosity, low density, and excellent thermal insulating ability. However, the fabrication of PI aerogels is still restricted to the traditional molding process, and it is often challenging to prepare high-performance PI aerogels with complex 3D structures. Interestingly, renewable nanomaterials such as cellulose nanocrystals (CNCs) may provide a unique approach for 3D printing, mechanical reinforcement, and shape fidelity of the PI aerogels. Herein, we proposed a facile water-based 3D printable ink with sustainable nanofillers, cellulose nanocrystals (CNCs). Polyamic acid was first mixed with triethylamine to form an aqueous solution of polyamic acid ammonium salts (PAAS). CNCs were then dispersed in the aqueous PAAS solution to form a reversible physical network for direct ink writing (DIW). Further freeze-drying and thermal imidization produced porous PI/CNC composite aerogels with increased mechanical strength. The concentration of CNCs needed for DIW was reduced in the presence of PAAS, potentially because of the depletion effect of the polymer solution. Further analysis suggested that the physical network of CNCs lowered the shrinkage of aerogels during preparation and improved the shape-fidelity of the PI/CNC composite aerogels. In addition, the composite aerogels retained low thermal conductivity and may be used as heat management materials. Overall, our approach successfully utilized CNCs as rheological modifiers and reinforcement to 3D print strong PI/CNC composite aerogels for advanced thermal regulation.

Evaluation of physicochemical properties and catalytic activity of poly(PMDAH-co-ODA/PPDA) nanocomposites towards the removal of toxic pollutants

Synthesis of Polyimides (PIs) between pyromellitic dianhydride (PMDAH) and oxydianiline (ODA) or p-phenylenediamine (PPDA) in the presence and absence of V₂O₅ and Ag nanoparticles (NPs) were carried out under N₂ atmosphere at 160 °C for 5 h with vigorous stirring in N-methylpyrrolidone (NMP) solvent. The prepared PI and its nanocomposites were analyzed by FT-IR spectroscopy, ¹H NMR spectroscopy, FE-SEM, SEM, DSC and TGA like analytical instruments. The FE-SEM showed various surface morphologies for different PI nanocomposites. The particle size of the prepared nanoparticles was calculated as less than 60 nm for Ag and 15 nm for V₂O₅ nanoparticles by HR-TEM. The PI nanocomposites embedded with Ag nanoparticles (P2 and P5) showed a higher thermal stability than the pristine PIs (P1 and P4) and PI/V₂O₅ nanocomposites (P3 and P6). Further, the possible application of metal (Ag) and metal oxide (V₂O₅) NPs embedded PI nanocomposites was assessed on the catalytic reduction of highly toxic Cr(VI), Rhodamine 6G (R6G) dye and p-nitrophenol (NiP) pollutants with the help of a reducing agent (NaBH₄). The apparent rate constant (k_app) values were calculated to assess the catalytic efficiency of the prepared PI and its nanocomposites. The PI/Ag nanocomposite (P2) system showed an efficient catalytic reduction than the other systems.

Highly Stable Porous Polyimide Sponge as a Separator for Lithium-metal Secondary Batteries

To inhibit Li-dendrite growth on lithium (Li)-metal electrodes, which causes capacity deterioration and safety issues in Li-ion batteries, we prepared a porous polyimide (PI) sponge using a solution-processable high internal-phase emulsion technique with a water-soluble PI precursor solution; the process is not only simple but also environmentally friendly. The prepared PI sponge was processed into porous PI separators and used for Li-metal electrodes. The physical properties (e.g., thermal stability, liquid electrolyte uptake, and ionic conductivity) of the porous PI separators and their effect on the Li-metal anodes (e.g., self-discharge and open-circuit voltage properties after storage, cycle performance, rate capability, and morphological changes) were investigated. Owing to the thermally stable properties of the PI polymer, the porous PI separators demonstrated no dimensional changes up to 180 °C. In comparison with commercialized polyethylene (PE) separators, the porous PI separators exhibited improved wetting ability for liquid electrolytes; thus, the latter improved not only the physical properties (e.g., improved the electrolyte uptake and ionic conductivity) but also the electrochemical properties of Li-metal electrodes (e.g., maintained stable self-discharge capacity and open-circuit voltage features after storage and improved the cycle performance and rate capability) in comparison with PE separators.

Polyimide-Coated Glass Microfiber as Polysulfide Perm-Selective Separator for High-Performance Lithium-Sulphur Batteries

Although numerous research efforts have been made for the last two decades, the chronic problems of lithium-sulphur batteries (LSBs), i.e., polysulfide shuttling of active sulphur material and surface passivation of the lithium metal anode, still impede their practical application. In order to mitigate these issues, we utilized polyimide functionalized glass microfibers (PI-GF) as a functional separator. The water-soluble precursor enabled the formation of a homogenous thin coating on the surface of the glass microfiber (GF) membrane with the potential to scale and fine-tune: the PI-GF was prepared by simple dipping of commercial GF into an aqueous solution of poly(amic acid), (PAA), followed by thermal imidization. We found that a tiny amount of polyimide (PI) of 0.5 wt.% is more than enough to endow the GF separator with useful capabilities, both retarding polysulfide migration. Combined with a free-standing microporous carbon cloth-sulphur composite cathode, the PI-GF-based LSB cell exhibits a stable cycling over 120 cycles at a current density of 1 mA/cm² and an areal sulphur loading of 2 mgS/cm² with only a marginal capacity loss of 0.099%/cycle. This corresponds to an improvement in cycle stability by 200%, specific capacity by 16.4%, and capacity loss per cycle by 45% as compared to those of the cell without PI coating. Our study revealed that a simple but synergistic combination of porous carbon supporting material and functional separator enabled us to achieve high-performance LSBs, but could also pave the way for the development of practical LSBs using the commercially viable method without using complicated synthesis or harmful and expensive chemicals.

Highly Compressible and Robust Polyimide/Carbon Nanotube Composite Aerogel for High-Performance Wearable Pressure Sensor

Wearable pressure sensors are in great demand with the rapid development of intelligent electronic devices. However, it is still a huge challenge to obtain high-performance pressure sensors with high sensitivity, wide response range, and low detection limit simultaneously. Here, a polyimide (PI)/carbon nanotube (CNT) composite aerogel with the merits of superelastic, high porosity, robust, and high-temperature resistance was successfully prepared through the freeze drying plus thermal imidization process. Benefiting from the strong chemical interactions between PI and CNT and stable electrical property, the composite aerogel exhibits versatile and superior brilliant sensing performance, which includes wide sensing range (80% strain, 61 kPa), ultrahigh sensitivity (11.28 kPa^-1), ultralow detection limit (0.1% strain, <10 Pa), fast response time (50 ms) and recovery time (70 ms), remarkable long-term stability (1000 cycles), and exceptional detection ability toward different deformations (compression, distortion, and bending). Furthermore, the composite aerogel also shows stable sensing performance after annealing under different high temperatures and good thermal insulation property, making it workable in various harsh environments. As a result, the composite aerogel is suitable for the full-range human motion detection (including airflow, pulse, vocal cord vibration, and human movement) and precise detection of the pressure distribution when it is assembled into E-skin, demonstrating its great potential to serve as a high-performance wearable pressure sensor.

Polyimide-Based PolyHIPEs Prepared via Pickering High Internal Phase Emulsions

Pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) oligoimide particles and PMDA-ODA poly(amic acid) salt (PAAS) were synthesized and used as stabilizers to prepare oil-in-water Pickering high internal phase emulsions (HIPEs). The stability of the Pickering HIPEs was investigated by dispersion stability analysis. Polyimide-based polyHIPEs could be prepared through freeze-drying and subsequent thermal imidization of the Pickering HIPEs. The characteristics of the polyHIPEs, including their morphology, porosity, thermal decomposition temperature, and compression modulus, were investigated. The thermal decomposition temperature (T₁₀) of the polyHIPEs was very high (>530 °C), and their porosity was as high as 92%. The polyimide-based polyHIPEs have the potential to be used in high-temperature environments.

Ultrathin Graphene Intercalation in PEDOT:PSS/Colorless Polyimide-Based Transparent Electrodes for Enhancement of Optoelectronic Performance and Operational Stability of Organic Devices

A novel flexible transparent electrode (TE) having a trilayer-stacked geometry and high optoelectronic performance and operational stability was fabricated by the spin coating method. The trilayer was composed of an ultrathin graphene (Gr) film sandwiched between a transparent and colorless polyimide (TCPI) layer and a methanesulfonic acid (MSA)-treated poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer containing dimethylsulfoxide and Zonyl fluorosurfactant (designated as MSA-PDZ film). The introduction of solution-processable TCPI enabled the direct formation of high-quality graphene on organic surfaces with a clean interface. Stable doping of graphene with the MSA-PDZ film enabled tuning of the inherent work function and optoelectronic properties of the PEDOT:PSS films, leading to a high figure of merit of ∼70 in the as-fabricated TEs. Particularly, from multivariate and repetitive harsh environmental tests ( T = -50 to 90 °C, over 90 RH%), the TCPI/Gr heterostructure exhibited excellent tolerance to mechanical and thermal stresses and gas barrier properties that protected the MSA-PDZ film from exposure to moisture. Owing to the synergetic effect from the TCPI/Gr/MSA-PDZ anode structure, the TCPI/Gr/MSA-PDZ-based polymer light-emitting diodes showed highly improved current and power efficiencies with maxima as high as 20.84 cd/A and 22.92 lm/W, respectively (comparable to those of indium tin oxide based PLEDs), in addition to much enhanced mechanical flexibility.

3D Printing All-Aromatic Polyimides Using Stereolithographic 3D Printing of Polyamic Acid Salts

Polyamic acid (PAA) salts are amenable to photocuring additive manufacturing processes of all-aromatic polyimides. Due to an all-aromatic structure, these high-performance polymers are exceptionally chemically and thermally stable but are not conventionally processable in their imidized form. The facile addition of 2-(dimethylamino)ethyl methacrylate (DMAEMA) to commercially available poly(4,4'-oxydiphenylene pyromellitamic acid) (PMDA-ODA PAA) afforded ultraviolet curable PAA salt solutions. These readily prepared solutions do not require multistep synthesis, exhibited fast gel times (<5 s), and rendered high G' gel-state moduli. Vat photopolymerization 3D printing afforded self-supporting organogels. Subsequent thermal treatment rendered the cross-linked PAA precursor to all-aromatic PMDA-ODA polyimide. This fast and facile strategy makes PMDA-ODA polyimides accessible in three dimensions and offers impact on aerospace or automotive technologies.

Counterion-Induced Control of the Colloidal State of Polyamic Acid Nanoparticles for Electrophoretic Deposition

Optimizing the colloidal state of polyamic acid (PAA) nanoparticles is essential for achieving a uniform and high-performance polyimide coating by electrophoretic deposition (EPD) on metal substrates of various shapes. In this paper, we report two important roles of the counterions in the formation of PAA colloids for EPD, which, to date, have not been recognized. First, when tertiary alkyl amines are used to neutralize PAA, the polarity of neutralizing counterions determines the size and stability of the PAA colloidal particles. The polarity can be finely tuned by using two different tertiary alkyl amines containing polar and nonpolar groups and adjusting the molar ratio. Depending on the polar/nonpolar ratio, various states of PAA colloids were obtained, including dissolved state, stable colloid, and aggregates. Second, we observed that the confined counterions inside PAA nanoparticles can act as an imidization catalyst during the thermal annealing process. It is revealed that some fraction of the counterion species, mostly having nonpolar groups, is not drawn toward the counter electrode and remains inside the PAA nanoparticles during the EPD process. Optimizing the polarity eventually allowed us to form uniform EPD coatings with high dielectric strengths.

Seedless synthesis and SERS characterization of multi-branched gold nanoflowers using water soluble polymers

We report for the first time, the aqueous-based synthesis of multibranched, monodispersed gold nanoflowers (AuNFs) using pyromellitic dianhydride-p-phenylene diamine - PPDDs at room temperature. AuNF synthesis was achieved using PPDDs that converts Au precursor (Au³⁺) into AuNFs while serving as both the reducing and directional agent. The resulting branched AuNFs exhibited different degrees of anisotropy and protuberance lengths obtained by modulating the ratio of PPDDs and HAuCl₄·3H₂O. The surface roughness obtained ranged from small bud-like protuberances to elongated spikes, which enabled the tuning of the optical properties of the nanoparticles from ∼450 to 1100 nm. Systematic analysis revealed that the generation of urchin-like particles as well as their size depended on the PPDDs/HAuCl₄·3H₂O ratio. At a medium concentration of the precursor, spherical nanoparticles were formed. Whereas at lower precursor concentrations, urchin-like nanoparticles were obtained with their size and protuberances length increasing at even lower HAuCl₄·3H₂O concentration. Increasing the temperature to 100 °C resulted in the enhancement of the anisotropy of the AuNFs. The resulting gold nanoflowers exhibited an enhanced performance in surface-enhanced Raman scattering (SERS). This work provides a unique approach for anisotropic particle synthesis using water soluble polymer and greener approaches. The fabricated AuNFs exhibited variable UV-vis absorption and SERS enhancement as a function of branch morphology, indicating their potential application in biolabeling, biosensing, imaging, and therapeutic applications.

Synthesis, characterization, and enhanced properties of novel graphite-like carbon nitride/polyimide composite films

In this article, polyimide (PI) composite films reinforced by graphitic carbon nitride (g-C3N4) have been synthesized using the in situ polymerization process via thermal imidization. Poly (amic acid) (PAA) solutions were prepared from pyromellitic dianhydride (PMDA) and 4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy) dianiline (BAPP) in N,N-dimethylacetamide (DMAc) solvent. The different amounts of g-C3N4 obtained from the direct pyrolysis of dicyandiamide (DCDA) at 600°C were incorporated into PAA matrix, which formed g-C3N4/PI composite films by thermal imidization. The morphological structures of the synthesized g-C3N4 and g-C3N4/PI composite films were characterized using fourier transform infrared spectroscopy, x-ray diffraction, scanning electron microscopy and transmission electron microscopy. With 2 wt% g-C3N4 incorporated, the tensile strength and elongation at break of g-C3N4/PI composites were increased by about 23% and 21%, respectively, due to the strong interaction between the g-C3N4 particles and PI. Thermogravimetric analysis indicated that the incorporation of g-C3N4 improved the thermal stability of the PI at low g-C3N4 content. Besides, the dielectric and optical properties of these composites were also studied in this article.

Synthesis of silver nanocubes with controlled size using water-soluble poly(amic acid) salt as the intermediate via a novel ion-exchange self-assembly technique

Here, we report for the first time on the successful fabrication of monodispersed silver nanocubes with regular shape and controlled size in the solid phase via a novel ion-exchange self-assembly technique by using water-soluble poly(amic acid) salt as the intermediate and silver nitrate as the metal precursor. By simply altering the annealing times at high temperature, the size of the silver nanocubes could be finely tuned in the range of 90-160 nm in the present case. Further attempts with different metal salts show that the present method is also feasible for other metal species and might be universal.