Research Progress and Application of Polyimide-Based Nanocomposites.

Polyimide (PI) is one of the most dominant engineering plastics with excellent thermal, mechanical, chemical stability and dielectric performance. Further improving the versatility of PIs is of great significance, broadening their application prospects. Thus, integrating functional nanofillers can finely tune the individual characteristic to a certain extent as required by the function. Integrating the two complementary benefits, PI-based composites strongly expand applications, such as aerospace, microelectronic devices, separation membranes, catalysis, and sensors. Here, from the perspective of system science, the recent studies of PI-based composites for molecular design, manufacturing process, combination methods, and the relevant applications are reviewed, more relevantly on the mechanism underlying the phenomena. Additionally, a systematic summary of the current challenges and further directions for PI nanocomposites is presented. Hence, the review will pave the way for future studies.

An extensive pharmacological evaluation of novel anti-nociceptive and IL-6 targeted anti-inflammatory guaiane-type sesquiterpenoids from Cinnamomum migao H. W. Li through in-depth in-vitro, ADMET, and molecular docking studies.

Guaiane-type sesquiterpenoids are most prevalent in the genus Cinnamomum. Hence this study investigates the structures, anti-nociceptive and IL-6 targeted anti-inflammatory potential of three novels C-14 guaiane-type sesquiterpenoids and two new monoterpenoids, isolated from Cinnamomum migao. The structures were precisely confirmed and characterized through the modern chromatographic and spectroscopic techniques of HRESIMS, 1D NMR, 2D NMR, experimental circular dichroism (ECD), and calculated (ECD). Novel sesquiterpenoids 1 and 2 exhibited significant anti-inflammatory activities against the NO production and pro-inflammatory cytokines. Their IC50 values were determined as 9.52 and 13.42 µΜ against IL-6 mRNA, respectively. Similarly, subcutaneous injection of n-BuT and EA extracts showed a dose-dependent suppression of formalin-induced tonic biting/licking responses during the tonic antinociceptive phase. Furthermore, absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis of guaiane-type sesquiterpenoids 1 and 2 displayed that both compounds have a high level of GIT absorption, with a high zone of safety for cardiac and hepatotoxicity and no inhibition of cytochromes. In addition, molecular docking and simulation studies strengthen the anti-inflammatory potential of sesquiterpene 2 which showed a good binding affinity with IL-6 protein. Overall the inclusive results showed that the extracts and newly isolated guaiane-type sesquiterpenoids from C. migao will provide new evidence for the traditional use of this species to treat inflammation and nociception.

Synthesis of a Novel Rigid Semi-Alicyclic Dianhydride and Its Copolymerized Transparent Polyimide Films' Properties.

A new series of colorless polyimides (CPIs) with outstanding thermal properties and mechanical properties were fabricated by the copolymerization of a novel dianhydride and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 2,2'-bistrifluoromethyl benzidine (TFDB). The novel dianhydride, 10-oxo-9-phenyl-9-(trifluoromethyl)-9,10-dihydroanthracene-2,3,6,7-tetraacid dianhydride (3FPODA), possessed a rigid semi-alicyclic structure, -CF3 and phenyl side groups, and an active carbonyl group. Benefitting from the special structure of 3FPODA, the glass transition temperatures (Tg) of the new CPIs improved from 330 °C to 377 °C, the coefficient of thermal expansion (CTE) decreased from 46 ppm/K to 24 ppm/K, and the tensile strength (TS), tensile modulus (TM), and elongation at break (EB) increased from 84 MPa to 136 MPa, 3.2 GPa to 4.4 GPa, and 2.94% to 4.13% with the increasing amount of 3FPODA, respectively. Moreover, the active carbonyl group of the 3FPODA could enhance the CPI's adhesive properties. These results render the new dianhydride 3FPODA an ideal candidate monomer for the fabrication of high-performance CPIs.

Advanced Dual-Function Hollow Copper-Sulfide-Based Polyimide Composite Window Film Combining Near-Infrared Thermal Shielding and Organic Pollutants' Photodegradation.

Window-film-integrated, near-infrared (NIR) absorption-based nanomaterials are of great interest in terms of numerous demands to reduce energy consumption, especially in buildings and vehicles. However, the question of how to effectively manage thermal energy generated from NIR harvesting in light-absorbing materials, rather than being wasted or causing negative effects, remains challenging. Herein, hollow copper sulfide (Cu2-xS) on colorless polyimide (PI) films, enabling them to be well-dispersed and robustly adhered, underwent in situ growth fabrication and were utilized as NIR-thermal-shielding and organic-pollutant-removal dual-function window films. Due to strong NIR absorbance, arising from the heavy hole-doping (copper cation deficiency), the Cu2-xS/PI composite film exhibited great promise for use in the filtration of the NIR spectrum. By monitoring Cu2-xS densities, its NIR-shielding efficiency reached 69.4%, with hundred-percent UV blocking and consistent performance within the reliability (85 °C/85%RH) tests over one week as well as 5000 bending cycles. The integration of the films into model cars and building windows exhibited excellent thermal-shielding performance upon exposure to direct sunlight. Moreover, benefiting from the distinctive distribution of Cu2-xS, the additional thermal energy (holes) generated in NIR absorption was successfully utilized. The densely surface-confined hollow structure of Cu2-xS on PI significantly endowed good formaldehyde catalytic capacity, with removal efficiency reaching approximately 72% within 60 min and a negligible decline after quartic reuse. These integration methodologies enable the promising fabrication of a high-performance, bifunctional window film combining thermal shielding and indoor organic pollutant removal.

Sputtering Flexible VO2 Films for Effective Thermal Modulation.

Flexible vanadium dioxide (VO2) thermochromic films show great potential for large-scale fabrication and possess broader applications compared with VO2 coatings on rigid substrates. However, the fabrication of flexible VO2 films remains a challenge so far, leading to the scarcity of research on flexible VO2 films for smart windows. With the aim to obtain a flexible VO2-based films with excellent optical properties and a long service life, we designed and successfully fabricated a flexible ITO/VO2/ITO (IVI) film on the colorless transparent polyimide substrate, which could be directly attached to glasses for indoor temperature modulation. This flexible IVI film effectively enhances the luminous transmittance (Tlum) and solar modulation ability (ΔTsol) (15 and 68% increase relative to a VO2 single layer), reduces the thermal emissivity (εT) (50.7% decrease relative to a VO2 single layer), and exhibits better durability than previously reported structures. Such excellent comprehensive performance offers it great potential in practical applications on smart windows. This work is supposed to provide a new strategy for facile direct fabrication of flexible VO2 films and broaden the applications of flexible VO2 in more coatings and devices.

Conjugated zwitterionic polyelectrolyte as the charge injection layer for high-performance polymer light-emitting diodes.

A new zwitterionic conjugated polyelectrolyte without free counterions has been used as an electron injection material in polymer light-emitting diodes. Both the efficiency and maximum brightness were considerably improved in comparison with standard Ca cathode devices. The devices showed very fast response times, indicating that the improved performance is, in addition to hole blocking, due to dipoles at the cathode interface, which facilitate electron injection.

Tuning the electronic coupling in a low-bandgap donor-acceptor copolymer via the placement of side-chains.

We present a spectroscopic and theoretical investigation of the effect of the presence and position of hexyl side-chains in the novel low-bandgap alternating donor-acceptor copolymer poly[bis-N,N-(4-octylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine-alt-5,5'-4',7',-di-2-thienyl-2',1',3'-benzothiadiazole] (T8TBT). We use electronic absorption and Raman spectroscopic measurements supported by calculations of chain conformation, electronic transitions, and Raman modes. Using these tools, we find that sterically demanding side-chain configurations induce twisting in the electronic acceptor unit and reduce the electronic interaction with the donor. This leads to a blue-shifted and weakened (partial) charge-transfer absorption band together with a higher photoluminescence efficiency. On the other hand, sterically relaxed side-chain configurations promote coupling between donor and acceptor units and exhibit enhanced absorption at the expense of luminescence efficiency. The possibility of tuning the donor-acceptor character of conjugated polymers by varying the placement of side-chains has very important ramifications for light emitting diode, Laser, display, and photovoltaic device optimization.

Formation of nanopatterned polymer blends in photovoltaic devices.

In this paper, we demonstrate a double nanoimprinting process that allows the formation of nanostructured polymer heterojunctions of composition and morphology that can be selected independently. We fabricated photovoltaic (PV) devices with extremely high densities (10(14)/mm(2)) of interpenetrating nanoscale columnar features in the active polymer blend layer. The smallest feature sizes are as small as 25 nm on a 50 nm pitch, which results in a spacing of heterojunctions at or below the exciton diffusion length. Photovoltaic devices based on double-imprinted poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (F8TBT)/ poly(3-hexylthiophene) (P3HT) films are among the best polymer-polymer blend devices reported to date with a power conversion efficiency (PCE, eta(e)) of 1.9%.

Highly Luminescent and Stable CsPbI3 Perovskite Nanocrystals with Sodium Dodecyl Sulfate Ligand Passivation for Red-Light-Emitting Diodes.

CsPbI3 perovskite nanocrystals (NCs) have recently emerged as promising materials for optoelectronic devices because of their superior properties. However, the poor stability of the CsPbI3 NCs induced by easy ligand desorption represents a key issue limiting their practical applications. Herein, we report stable and highly luminescent black-phase CsPbI3 NCs passivated by novel ligands of sodium dodecyl sulfate (SDS). Theoretical calculation results reveal a stronger adsorption energy of SDS molecules at the CsPbI3 surface than that of commonly used oleic acid. As a result, the defect formation caused by the ligand loss during the purification process is greatly suppressed. The optimized SDS-CsPbI3 NCs exhibit significantly reduced surface defects, much enhanced stability, and superior photoluminescence efficiency. The red perovskite light-emitting diodes based on the SDS-CsPbI3 NCs demonstrate an external quantum efficiency of 8.4%, which shows a 4-fold improvement compared to the devices based on the oleic acid-modified CsPbI3 NCs.

Guaiane-type sesquiterpenoids from Cinnamomum migao H. W. Li: And their anti-inflammatory activities.

The phytochemical assessment of Cinnamomum migao H. W. Li fruits illustrated the isolation and identification of ten undescribed guaiane-type sesquiterpenoids "miganoids A-J″ and one undescribed sesquiterpene "7(S)-(hydroxypropanyl)-3-methyl-2-(4-oxopentyl) cyclohex-2-en-1-one". The extensive analysis of HRESIMS, 1D NMR, 2D NMR, experimental circular dichroism (ECD), and calculated (ECD) analysis entirely corroborated the configuration and confirmation of these isolated compounds. Moreover, the anti-inflammatory properties of the reported compounds were established by determining the LPS induced nitric oxide production. In the current study, miganoid C is testified the most active compound with about 89% NO inhibition. Additionally, miganoids C, E, and G also exhibited moderate inhibitory effects against the pro-inflammatory cytokines (TNF-α, IL-1ß, and IL-6). The IC50 values for miganoid C and miganoid G were determined as 19.4 and 14.5 µΜ against TNF-α mRNA, respectively.

Functionalized Amphiphilic Diblock Fullerene Derivatives as a Cathode Buffer Layer for Efficient Inverted Organic Solar Cells.

The amphipathic interface layer sandwiched between cathode and active layers had always played a role to balance interface compatibility and interfacial energy barriers in inverted organic solar cell (OSC) devices. Two functionalized amphiphilic diblock fullerene derivatives named C60-2DPE and C60-4HTPB were synthesized and applied as an interface layer in modifying zinc oxide (ZnO). Based on their amphipathic characteristics, the solvent treatment was introduced to cause an obvious self-assembly of the two materials on ZnO. The introduced cathode buffer layer could improve the interface compatibility between ZnO and the organic active layer effectively with its amphipathic blocks. Based on the PTB7-Th:PC71BM system, the OSC devices with a functionalized fullerene derivative layer could reach a power conversion efficiency of 9.21 and 8.86% for C60-2DPE and C60-4HTPB , respectively.

Large-Scale Flexible Surface-Enhanced Raman Scattering (SERS) Sensors with High Stability and Signal Homogeneity.

Flexible surface-enhanced Raman scattering (SERS) sensors have attracted great attention as a portable and low-cost device for chemical and bio-detection. However, flexible SERS sensors tend to suffer low signal spatial homogeneity due to the uneven distribution of active plasmonic nanostructures (hot spots) and quick degradation of their sensitivity due to low adhesion of hot spots and flexible substrates during fast sampling. Herein, a large-area (20 × 20 cm2) polyimide (PI)-based SERS sensor is exploited for trace detection with high signal homogeneity and stability. The SERS sensor is constructed from PI through in situ growth of silver and gold core-shell nanoparticles (Ag@Au NPs) based on chemical reduction and galvanic replacement processes. Benefiting from the abundant carboxyl groups on the surface-cleaved PI, densely and uniformly distributed Ag@Au NPs are successfully prepared on the film under ambient conditions. The high Raman enhancement factor (EF) (up to 1.07 × 107) and detection capability with low nanomolar (10-9 M) detection limits are obtained for this flexible SERS sensor. The uniform Raman signals in the random region show good signal homogeneity with a low variation of 8.7%. Moreover, the flexible SERS sensor exhibited superior efficiency and durability after storage for 30 days even after 500 cycles of mechanical stimuli (bending or torsion). The residue of pesticide thiram (tetramethylthiuram disulfide, TMTD) has been rapidly traced by direct sampling from the apple surface, and a sensitivity of 10 ng/cm2 for TMTD was achieved. These findings show that the PI-based SERS sensor is a very strong candidate for broad and simple utilization of flexible SERS for both laboratory and commercial applications in chemical and biomolecule detections.

In Situ Synthesis of Ultrastable CsPbBr3 Perovskite Nanocrystals Coated with Polyimide in a CSTR System.

The poor stability of perovskite nanocrystals (NCs) is one of the major obstacles for their application in optoelectronic devices. Herein, we develop an easy in situ strategy for preparing polyimide (PI)-coated single-particle CsPbBr3 NCs in a continuous stirred-tank reactor system. Benefiting from the protection of the thick polyimide layer, these PI-coated CsPbBr3 NCs show excellent stability against severe environments such as water, heat, oxygen, and light. Meanwhile, time-resolved photoluminescence and ultrafast transient absorption spectroscopy revealed that the polyimide (PI) polymer contributes to passivating the surface defects of the CsPbBr3 NCs, giving CsPbBr3/PI NCs a higher photoluminescence quantum yield. Thanks to the performances of high luminescent efficiency and stability, these green-emitting perovskite CsPbBr3/PI NCs show promising potentials in the fields of solid-state lighting and display.

Ion-induced formation of charge-transfer states in conjugated polyelectrolytes.

We use time-resolved optical spectroscopy to demonstrate that the luminescence quenching observed when ions are incorporated in films of conjugated polymers can be explained by the formation of charge-transfer (CT) states that are stabilized by the Coulomb field of ions. Our investigation is focused on a conjugated polyelectrolyte (CPE) derived from F8BT (poly(9,9'-dioctylfluorene-alt-benzothiadiazole)). The statistical copolymer contains tetra-alkyl ammonium moieties and BF(4)(-) counteranions attached to a moderate (approximately 7%) density of polymer alkyl side chains, providing a film morphology comparable to F8BT but with ions distributed on the length scale of exciton diffusion. The ionic substituents have little influence over the polymers electronic absorption and emission properties in solution, however photoluminescence (PL) quantum efficiency (approximately 6%) is considerably lower for the polyelectrolyte compared with F8BT (approximately 60%) in thin films. Time-resolved PL spectroscopy reveals that the primary exciton lifetime is shortened in the polyelectrolyte and a red-shifted CT emission peak with a longer lifetime emerges. Transient absorption spectroscopy of thin films enables us to detect CT states that persist beyond the primary decay and are found to be immobile. The PL intensity of the partially ionic film is found to increase with decreasing temperature, consistent with thermally activated exciton hopping (E(act) = 28 meV) prior to formation of CT states at ionic regions. We suggest that ion-induced stabilization of CT states is a general phenomenon in CPEs, which raises the possibility that ions might be arranged to direct the flow of excitons toward charge-separating interfaces in polymer photovoltaic devices.

Core-independent approach for polymer brush-functionalised nanomaterials with a fluorescent tag for RNA delivery.

Here we describe a core-independent approach enabling the grafting of polymer brushes from the surface of nanomaterials and microparticles for oligonucleotide delivery. This method is based on the adsorption of a polyelectrolyte macroinitiator (MI) combined with a fluorescent conjugated polymer for efficient and stable labelling. This allows dense brushes to be generated, with growth kinetics comparable to those observed from mono-functional initiators, for the imaging of nanomaterial cellular localisation and uptake. We also study the impact of brush chemistry on interactions with cell membranes and on transfection efficiency. The method we report offers a unique freedom of design of the core size and shape as well as surface chemistry, whilst enabling tagging, for the study of transfection processes or theragnostic applications.

Lithium-Ion-Based Conjugated Polyelectrolyte as an Interface Material for Efficient and Stable Non-Fullerene Organic Solar Cells.

An eco-friendly n-type water/alcohol-soluble conjugated polyelectrolyte PFEO SO3 Li was synthesized and applied as a cathode interfacial layer in organic solar cells. The π-delocalized polyfluorene backbone has an intimate connection with the hydrophobic active layer, and the side chain with lithium ion may move toward the ZnO layer through the self-assembly property of conjugated polyelectrolytes. UV photoelectron spectroscopy indicated that modification with PFEO SO3 Li dramatically lowers the work function of indium-doped tin oxide (ITO)/ZnO and may form strong interfacial dipoles between ZnO and the active layer. Meanwhile, introduction of lithium ions as spectator cations may contribute to reduction of the intrinsic surface defects of ZnO. The green emission in the photoluminescence spectrum of ZnO disappeared after modification with PFEO SO3 Li. In addition, the roughness of ZnO barely changed after coating with PFEO SO3 Li, and the surface became more hydrophobic, which demonstrates that the thin conjugated polyelectrolyte layer exhibits good adhesion with both ZnO and the active layer. These phenomena indicate that the introduction of PFEO SO3 Li makes ITO/ZnO an efficient cathode. As a result, inverted organic solar cell devices with ZnO/PFEO SO3 Li double-interlayers exhibit high efficiencies of 11.7 and 10.6 % for PBDB-T:IT-M and PBDB-T:ITIC blend systems, respectively.

Flexible Perovskite Solar Cells via Surface-Confined Silver Nanoparticles on Transparent Polyimide Substrates.

We report about a flexible substrate incorporating surface-confined silver nanoparticles on transparent polyimide (PI). The incorporated silver nanoparticles (Ag NPs), which possessed excellent adhesive strength with the PI substrate, induced localized surface plasmon resonance and light scattering effects by changing the particle size and interparticle distance to promote light harvesting in the perovskite solar cells. Moreover, the reduced sheet resistance was beneficial for the charge extraction and transportation in the devices when high-conductivity poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS, PH1000) was deposited on the Ag NP-confined PI serving as a flexible bottom electrode. A power conversion efficiency of 10.41% was obtained for the flexible perovskite solar cells based on a Ag NP-confined PI substrate (the particle size of the Ag NPs was 25 nm mixed with 40 nm), which was obviously enhanced in all parameters. Especially, a 61% improvement existed in the short-circuit current density compared to that based on the bare PI substrates. It indicates that the substrate would be a promising candidate for the development of flexible electronics.

Amphiphilic Diblock Fullerene Derivatives as Cathode Interfacial Layers for Organic Solar Cells.

A new amphiphilic diblock fullerene derivative [6,6]-phenyl-C61-butyricacid-4-(9,9,9',9'-tetrakis(3-bromopropyl)-9H,9'H-[2,2'-bifluoren]-7-yl)phenol-(N,N,N-trimethylpropan-1-aminium) bromide (C60-4TPB) was synthesized and applied in organic solar cells. Solvent annealing by toluene could obviously induce the self-assembly of the C60-4TPB layer, which can be tested by the measurements of the water contact angle. After the treatment with toluene, a vertical-like arrangement in the ultrathin layer of the C60-4TPB molecule will be formed between electron-collecting zinc oxide (ZnO) layers and the active layer (blend system of PTB7:PC71BM), leading to the improvement of the interfacial compatibility between the active layer and the ZnO layer. On the top surface of the C60-4TPB layer, the C60 molecules can be expected to induce the enrichment of PC71BM and block the hole, resulting in further increase in the open-circuit voltage (VOC) and fill factor (FF). After spin-coating the C60-4TPB solutions onto the ZnO layer with a concentration of 0.5 mg/mL in dimethyl sulfoxide, obviously improved performances were obtained with a power conversion efficiency of 8.07%, which can be attributed to the optimized interface morphology between hydrophilic ZnO and hydrophobic PTB7:PC71BM.

High Performance Soluble Polyimides from Ladder-Type Fluorinated Dianhydride with Polymorphism.

A novel rigid semi-alicyclic dianhydride 9,10-difluoro-9,10-bis(trifluoromethyl)-9,10-dihydroanthracene-2,3,6,7-tetracarboxylic acid dianhydride (8FDA) was reported, and its single crystal X-ray diffraction result revealed the existence of the polymorphic structure in this compound. The detail geometric configuration transition during the synthesized process was investigated, exhibiting a transition of from trans- to cis- when the hydroxyl groups were substituted by fluoride with diethylaminosulfur trifluoride (DAST). Compared with the dianhydride 4,4'-(Hexaflouroisopropylidene) diphthalic anhydride (6FDA) and 1S,2R,4S,5R-cyclohexanetetracarboxylic dianhydride (HPMDA), the resulting polyimide (PI) films based on 8FDA exhibited an obviously higher glass transition temperature (Tg, 401 °C) and a much lower coefficient of thermal expansion (CTE, 14 ppm K-1). This indicates that 8FDA is an ideal building block in high-performance soluble PIs with low CTE.

Amphiphilic conjugated block copolymers: synthesis and solvent-selective photoluminescence quenching.

A novel, amphiphilic, conjugated block copolymer is described, which was prepared by a Suzuki-type cross-coupling of 2-bromo-[9,9-bis(2-ethylhexyl)fluorene]-7-pinacolato boronate as an AB-type monomer and monobromo-substituted poly[3-(6-bromohexyl)thiophene] (Br-P3BrHT) as a polymeric end capper in the key step. PF-P3PHT (P2; PF = poly(9,9-dialkylfluorene); P3PHT = poly[3-(6-diethylphosphonato-hexyl)thiophene]) as the amphiphilic target polymer was then generated in a polymer-analogous conversion of the alkyl bromide side chains of the PF-P3BrHT (P1) precursor into polar alkyl phosphonate groups by reaction with triethyl phosphite. P2 shows a strong influence of the solvent polarity on the optical spectra (absorption, emission). Treatment of solutions of P2 in tetrahydrofuran (THF), a nonselective solvent, with increasing amounts of solvents that are selective for the polar polythiophene blocks (water) or the nonpolar polyfluorene blocks (hexane), respectively, results in the formation of two different types of core-shell aggregates, which show rather different optical properties (photoluminescence quenching, excitation energy transfer).