Low-temperature Polymerization Research Articles

A Novel Catalytic System of [O,O] Bidentate Titanium Complexes and Et2AlCl/Bu2Mg for the Production of Ultra‐High Molecular Weight Polyethylene

AbstractA bidentate ligand, 2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranol (ddbfOH), is used to synthesize the titanium complexes, ddbfOTi(OiPr)3(1) and (ddbfO)2Ti(OiPr)2(2). Combined with diethylaluminium chloride (Et2AlCl) and di‐n‐butylmagnesium (Bu2Mg), complexes 1 and 2 exhibit super high activity towards ethylene polymerization, and giving the ultra‐high molecular weight polyethylene (UHMWPE). After rationally optimizing the experimental conditions, the highest polymerization activity is achieved in both 1/ and 2/Et2AlCl/Bu2Mg catalytic systems (213.6×106 g‐PE⋅mol‐Ti−1 h−1, 142.8×106 g‐PE⋅mol‐Ti−1 h−1). The highest molecular weight (Mv =1905×104) can be achieved under a low polymerization temperature (−30 °C) at the expense of activity (3000 g‐PE⋅mol‐Ti−1 h−1). Additionally, through the investigation of various polymerization conditions on the activity and molecular weight of the catalytic system, we have found that the ratio of the catalyst and cocatalyst has a more significant impact on both activity and molecular weight.

The long-lasting maintenance of the pore structure achieves the stability of lithium metal batteries

The separator is considered critical to the safety and performance of lithium metal batteries (LMBs), however, the separator structure fails under high temperature conditions due to damage resulting in decreased mechanical strength, which causes short-circuiting of the battery. This paper describes a novel process to prepare stable and uniform dispersions of aramid nanofibers (ANFs) by bottom-up low-temperature polymerization, and then crosslink the ANFs with N2 plasma-treated polypropylene (PP) separator through capping isocyanate crosslinkers. The composite separator not only has excellent mechanical properties with hardness and modulus of elasticity up to 0.35 and 2.26 GPa, which is three times higher than the PP separator, but also has high-temperature thermal stability, the size maintenance rate reaches 99.8% at 200°C. Meanwhile, real-time monitoring of the pore size at different temperatures by synchrotron radiation small-angle X-ray scattering (SR-SAXS) showed that the pore radius of gyration was kept at 8.81 nm and the size change rate was only 22.8% at 200°C, which demonstrated that the composite separator had an outstanding ability to maintain the pore structure to ensure the stability of the ionic transport channel. Therefore, the crosslinked composite separator has greater potential for improving the performance and safety of LMBs in extreme high-temperature environments.

Energy-Efficient Smart Window Based on a Thermochromic Hydrogel with Adjustable Critical Response Temperature and High Solar Modulation Ability.

Thermochromic smart windows realize an intelligent response to changes in environmental temperature through reversible physical phase transitions. They complete a real-time adjustment of solar transmittance, create a livable indoor temperature for humans, and reduce the energy consumption of buildings. Nevertheless, conventional materials that are used to prepare thermochromic smart windows face challenges, including fixed transition temperatures, limited solar modulation capabilities, and inadequate mechanical properties. In this study, a novel thermochromic hydrogel was synthesized from 2-hydroxy-3-butoxypropyl hydroxyethyl celluloses (HBPEC) and poly(N-isopropylacrylamide) (PNIPAM) by using a simple one-step low-temperature polymerization method. The HBPEC/PNIPAM hydrogel demonstrates a wide response temperature (24.1-33.2 °C), high light transmittance (Tlum = 87.5%), excellent solar modulation (ΔTsol = 71.2%), and robust mechanical properties. HBPEC is a functional material that can be used to adjust the lower critical solution temperature (LCST) of the smart window over a wide range by changing the degree of substitution (DS) of the butoxy group in its structure. In addition, the use of HBPEC effectively improves the light transmittance and mechanical properties of the hydrogels. After 100 heating and cooling cycles, the hydrogel still has excellent stability. Furthermore, indoor simulation experiments show that HBPEC/PNIPAM hydrogel smart windows have better indoor temperature regulation capabilities than traditional windows, making these smart windows potential candidates for energy-saving building materials.

A New Polycyclic Naphthoxazine Resin: Facile Synthesis, Characterization, Polymerization, and Thermal Properties of Its Corresponding Thermosets.

A novel polycyclic naphthoxazine resin (NSA-thiq) is synthesized via N, O-acetal forming reaction between o-hydroxyl naphthaldehyde and 1,2,3,4-tetrahydroisoquinoline. The chemical structure of the monomer is investigated and confirmed by 1H and 13C NMR, Fourier-transform infrared (FT-IR) spectroscopy, and high-resolution mass spectrometry. Besides, the ring-opening polymerization behavior similar to ordinary benzoxazine resins is observed by differential scanning calorimetry (DSC) and in situ FT-IR analyses, leading to the formation of the phenolic cross-linked network. Notably, DSC thermograms indicate that the newly obtained polycyclic naphthoxazine resin exhibits much lower polymerization temperatures compared to many other reported benzoxazine or naphthoxazine resins. Moreover, the corresponding polybenzoxazine (poly(NSA-thiq)) shows comparable thermal stability in comparison with thermosets derived from monobenzoxazine resins. As a consequence of these unique performances, NSA-thiq is applied as a property modifier for a commercialized benzoxazine resin (BA-a). The glass transition temperature of copolymeric thermosets is enhanced without sacrificing too much thermal stability and heat resistance. Here, another series of naphthoxazine thermosetting resin is explored, which can provide more examples for constructing composites based on thermoset polymers.

Mechanism of SDBS functionalized PPy enhancing the electrochemical sensitivity of SPGE to dopamine and uric acid: Experimental and DFT investigations

A novel approach to enhance the electrochemical sensitivity of screen-printed graphene electrode (SPGE) to dopamine (DA) and uric acid (UA) utilizing sodium dodecylbenzene sulfonate (SDBS) functionalized polypyrrole (PPy) is presented. The functionalized PPy nanosheets (SDBS/PPy) were synthesized via low-temperature polymerization. The introduced dodecylbenzene sulfonate (DBS-) facilitated the dispersion of functionalized PPy nanosheets, resulting in a notably increased specific surface area. DA and UA adsorption behavior on PPy and SDBS/PPy surface was investigated using density functional theory (DFT). The adsorption energy of DA and UA on SDBS/PPy was 0.15 eV and 0.05 eV higher than that on PPy. The adsorption ability of DA and UA was greatly improved after doping DBS- in PPy. The electrochemical response of SDBS/PPy-modified SPGE (SDBS/PPy/SPGE) to different concentrations of DA and UA was evaluated. Compared with SPGE, the oxidation current sensitivity of SDBS/PPy/SPGE to DA increased from 0.08 μA·μM−1 to 0.13 μA·μM−1, the oxidation current sensitivity of SDBS/PPy/SPGE to UA increased from 0.01 μA·μM−1 to 0.04 μA·μM−1. Electrochemical measurement demonstrated that PPy doping with DBS- caused a unique improvement in DA and UA performance of SPGE.

Green synthesis of N-rich carbon dot-derived crosslinked covalent organic nanomaterial for multipurpose chromatographic applications.

Carbon dots (CDs) derived crosslinked covalent organic nanomaterials (CONs) possessing high specific surface area and abundant surface functional groups are considered to be potential candidates for multimodal chromatographic separations. Typically, the synthesis of CDs and CONs requires harsh reaction conditions and toxic organic solvents, hence, the pursuit of facile and mild preparation strategies is the goal of researchers. In this work, 3-aminopropyltriethoxysilane and D-glucose were used as nitrogen and carbon sources, respectively, to prepare amino-CDs (AmCDs) by rapid low-temperature polymerization rather than the common high-temperature and high-pressure reaction. Then, surface functionalization of the aminated silica gel was carried out in a deep eutectic solvent by using hydrophilic AmCDs and 1,3,5-triformylbenzene (TFB) as the functional monomers. Consequently, a novel N-rich CDs derived CON surface-functionalized silica gel (AmCDs-CON@SiO2) was obtained under mild reaction conditions. The combination of AmCDs and TFB created an ideal CON based chromatographicstationary phase. The incorporation of TFB not only contributed to the successful construction of a crosslinked CON, but also enhanced the interaction forces. The developed AmCDs-CON@SiO2 has a great potential for versatile applications in liquid chromatography. This study proposes a simple stationary phase preparation strategy by the surface modification of silica gel with CDs-based CON. Moreover, this study verified the application potential of CDs derived CON in chromatographic separation. This not only promotes the development of CDs in the field of liquid chromatographic stationary phase, but also provides some reference value for the wide application of cross-linked CON.

Preparation and Properties of Low-Dielectric Polyimide Films Containing Tert-Butyl.

The design of high-performance polyimide (PI) films and understanding the relationship of the structure-dielectric property are of great significance in the field of the microelectronics industry, but are challenging. Herein, we describe the first work to construct a series of novel tert-butyl PI films (denoted as PI-1, PI-2, PI-3, and PI-4) based on a low-temperature polymerization strategy, which employed tetracarboxylic dianhydride (pyromellitic anhydride, 3,3',4,4'-biphenyl tetracarboxylic anhydride, 4,4'-diphenyl ether dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic anhydride) and 4,4'-diamino-3,5-ditert butyl biphenyl ether as monomers. The results indicate that introducing tert-butyl branches in the main chain of PIs can enhance the free volume of the molecular chain and reduce the interaction between molecular chains of PI, resulting in a low dielectric constant. Particularly, the optimized PI-4 exhibits an excellent comprehensive performance with a high (5) wt% loss temperature (454 °C), tensile strength (117.40 MPa), and maximum hydrophobic angle (80.16°), and a low dielectric constant (2.90), which outperforms most of the results reported to date.

The promoting and inhibitory mechanism of interaction between waste tires and Spirulina on their co-pyrolysis

Energy utilization of biomass and waste is an important thrust for carbon emission reduction. Co-pyrolysis is conductive to efficiently converting algae and waste tires, due to their complementary pyrolysis characteristics. However, the influence of the interaction between algae and waste tires on co-pyrolysis behavior is still controversial, due to the internal mechanism of interaction is unclear. Therefore, in this study, mechanism experiments and theoretical calculations were used to comprehensively investigate the interaction mechanism between Spirulina (SP) and waste tires (WT). The co-pyrolysis of SP and WT can be divided into two main steps: low-temperature SP decomposition and high-temperature WT decomposition. The activation energies of WT and mixture increase with the conversion rate, while those of SP change little at low conversion rates (<60 %). The pyrolysis activation energies of mixture are lower than the theoretical values, as the blending ratio of SP below 50 %. The interaction between SP and WT has both promoting and inhibiting effects on the pyrolysis of mixture. The attack of free radicals from SP pyrolysis and ash in WT promotes the pyrolysis of mixture, but the low-temperature polymerization reactions and high-temperature aromatization reactions inhibit the release of pyrolysis products. The formation of benzene compound is promoted due to the attack of free radicals and the polymerization between SP and WT.

Development and Recent Progress of Hoses for Cryogenic Liquid Transportation.

Recently, the application of cryogenic hoses in the field of cryogenic media has become a hot topic, especially in the industry of offshore liquefied natural gas and aerospace field. However, the structure of cryogenic hoses is complex, and reasonable structural properties are required due to the harsh working conditions. There is still plenty of scope for further development to improve the performance in all aspects. In this paper, the current development status of cryogenic hoses for liquefied natural gas (LNG) transportation is reviewed first, including the types, manufacturers, structural forms, performance, and key technical challenges. And then, the recent progress and prospect of cryogenic hoses for cryogenic liquid transportation (such as LNG and liquid oxygen) are summarized, including structure design, low-temperature resistant polymers, liquid oxygen compatible polymers, and leakage monitoring technologies. This paper provides a comprehensive overview of the research development and application of cryogenic hoses. Moreover, future research directions have been proposed to facilitate its practical applications in aerospace.

Near-infrared Light-Induced Polymerizations: Mechanisms and Applications.

Photopolymerizations have garnered significant attention in polymer science due to their low polymerization temperature, high production efficiency, environmental friendliness, and spatial controllability. Despite these merits, the poor penetration and severe chemical damage from ultraviolet/visible (UV/Vis) light resources pose significant barriers to their success in conventional photopolymerizations. A recent breakthrough involving the utilization of near-infrared (NIR) laser with long wavelength has been exploited for diverse applications. With the combination of a NIR photosensitizer (PS), NIR-induced photopolymerizations have been successfully developed to alleviate the challenges in conventional methods. The enhancement of penetration depth and safety of NIR-induced photopolymerizations can contribute significantly to improving the efficiency of polymerization for production of intricate structures across various scales. In this concept, the typical types of PSs and polymerization mechanisms (PMs) within the NIR-induced photopolymerization systems have been classified in detail. Additionally, the applications of various polymers achieved by NIR-induced photopolymerizations are summarized. Furthermore, research directions and future challenges of this field are also discussed comprehensively.

High−molecular weight poly(2-substituted 1,3-diene)s using iminopyridine iron precatalysts at high polymerization temperature and low iron loading

The synthesis of a series of iron(II) dichloride complexes bearing iminopyridine (ImPy) ligands, differing in the substituents at the pyridine, bridging carbon and N−aryl ring is described (1-LHPh−7-LHS). The X-ray structures of some of them are presented. All the iron compounds and, for comparison, the already reported 8-LHPhP, that features bulky ortho isopropyl N−aryl substituents, have been investigated as precatalysts for the polymerization of 2-substituted 1,3-dienes, i.e., isoprene and β-myrcene, using a low excess of methylaluminoxane (MAO) as alkylating reagent, iron loading as low as 0.025 mol% and variable temperature up to 100 °C. The goal is to have insights into ligand effects on catalyst reactivity and selectivity and to recognize the most robust iron precatalysts to access high-molecular weight (MW) polymers using low iron loading and high polymerization temperature, which meets current demands of mild, operationally simple approach. Particularly, the ketimine 4-LMePh and 5-LPhPh are more stable and least prone to chain termination than all the aldimine parents. 4-LMePh and 5-LPhPh produce cis-1,4/3,4 ultra-high-MW poly(isoprene)s and solid high-MW poly(β-myrcene)s, while maintaining narrow and unimodal molecular weight distribution. In this study we intentionally kept the monomer conversion low to provide a valuable assessment of catalyst stability, uncorrupted by mass or heat transport limitations. Furthermore, the synthesis of the unsubstituted aminopyridine (AmPy) iron(II) dichloride complex 9-LAPh, analogue to 1-LHPh, is described. 9-LAPh has been demonstrated to be a valuable probe for stability studies. Given the variety of catalytic transformations and substrates for which (ImPy)FeCl2 precatalysts have promising reactivity and selectivity, those developed in this study offer promising applications also beyond the polymerization of 1,3-dienes.

High Vacuum Capable Fused Filament Fabrication 3D Printer, Part I: Low-Temperature Polymers and Early Lessons Learned

On-orbit manufacturing and assembly have become major research and development topics for government and commercial entities seeking the capability to build very large structures in space. Additive manufacturing is well suited to this paradigm since the process is highly automated, produces little material waste, and allows for a large degree of geometric freedom. This paper presents a design for a 3D printer that operates in high vacuum. The vacuum 3D printer has completed multiple thermal vacuum test campaigns, with dozens of parts printed to date using low-temperature thermoplastics. Testing of material coupons shows that samples printed in vacuum have strength properties generally within a standard deviation of samples printed at ambient pressure. The overall results from multiple successful tests of the vacuum 3D printer promote the feasibility of on-orbit additive manufacturing while exposed to the space environment. This paper is part one of a two-part series. Part I presents the results using a low-temperature hotend capable of printing hobby-grade materials and documents some initial findings and lessons learned for applying FFF in vacuum. Part II presents the results for a high-temperature hotend capable of printing engineering grade plastics that are suitable for on-orbit manufacturing. The combined results of the two papers in this series can be used to inform future on-orbit additive manufacturing applications as well as potential uses on future moon missions.

(Invited) Improvements in Thermal Budget and Film Properties Using Low Pressure Cure Technology for Advanced 3D Integration Packaging

3D advanced integration with Fan-Out Wafer-Level Packaging (FOWLP) and Fan-Out Panel Level Packaging (FOPLP) offers multiple benefits: heterogenous chip design and stacking, increased interconnect density, and improved performance. However, it also brings new requirements for more compact form factors, low thermal budget materials and processing, and lower cost. The materials, process, and fabrication of heterogenous integration on redistribution layers (RDLs) consisting of metal and polymer dielectrics have become important enablers of the move to advanced packaging applications. To achieve the low-stress and low-cost benefits required by advanced integrated devices, thermal budgets must be reduced throughout the heterogenous integration flow -- including the dielectric curing step, which demands the use of low temperature processing and reduced cure times.In this presentation, the low temperature and low pressure thermal polymerization of dielectric polyimides used for redistribution layers (RDLs) is reviewed. Specifically, this presentation illustrates the significant impact of the low pressure cure process in reducing temperature (20° to 50° lower) and cure times (up to a 50% reduction) while providing better mechanical (elongation%, tensile strength, Young’s modulus), thermal (TG, Td 1%, Td 5%), and electrical (Dk, Df, dielectric breakdown strength - DBS) properties for different types of dielectric polyimides, including the Fujifilm LTC-9300 series, the Asahi BL-300 series, and the Toray LT-8300 and PW-1500 series. The post-curing polymerization ratio (FT-IR) and film stress were studied and are described. Finally, a proposed mechanism for the described dielectric polyimides’ polymerization under reduced pressure is discussed.Ongoing developments in design, materials, process and fabrication for FOWLP and FOPLP devices continue to drive progress in 3D heterogenous integration. This study of thermal processing of dielectric polyimides at low pressure and shorter time demonstrates a promising technique to improve overall process flow by reducing thermal budget, stress, and cost.

Polymerization behaviors of benzoxazine isomers based-on meta-substituted phenols

The polymerization activity of benzoxazine is closely related to its molecular structure. In this work, two meta-substituted phenols, including 3-methoxyphenol and 3-chlorophenol, were separately reacted with aniline and paraformaldehyde, and two pairs of benzoxazine isomers were successfully synthesized. Their structures were confirmed by nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopy. The polymerization behaviors of the isomers were investigated by differential scanning calorimetry (DSC). The results indicated that 7-position benzoxazine isomers exhibited higher polymerization activity over 5-position isomers. The charges populations and CO bond lengths of the isomers calculated by molecular simulation well supported the results of experiment. This work provided new clues for developing novel benzoxazines with low polymerization temperatures.

Synthesis of phosphaphenanthrene-functional monobenzoxazine for enhancing thermal properties of polybenzoxazine thermosets

A facile approach to incorporate an intramolecular 6-membered ring hydrogen bond into a benzoxazine monomer containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) moiety has been developed, leading to a novel monobenzoxazine, ODOPB-pa. This monobenzoxazine was successfully synthesized via a Mannich condensation from 2-(6-oxido-6H-dibenz-[c,e][1,2]oxaphosphorin-1,4-dihydroxy phenylene (ODOPB), propargylamine and paraformaldehyde. The newly obtained ODOPB-pa possesses a relatively lower polymerization temperature than most commercialized benzoxazine resins. In addition, the intramolecular 6-membered ring hydrogen bond is identified as an essential feature in its polymerization behavior. The cured product, poly(ODOPB-pa), exhibits high thermal stability with a 5% weight loss temperature of 327 °C, and good flame retardant properties with a heat release capacity value of 119 Jg−1 K−1 and a total heat release value of 41 kJg−1. Moreover, ODOPB-pa was also applied to mix in different amounts (5, 10, 15 and 20 wt%) with a tri-functional benzoxazine bearing propargyl group, TH-pa. Notably, it has been demonstrated that the TH-pa/ODOPB-pa blend derived thermoset with 10 wt% ODOPB-pa exhibits the best thermal and flame retardant properties in consideration of the high glass transition temperature (312 °C) and very low heat release capacity value (56.5 Jg−1 K−1). These combined advantages highlight the potential of intramolecular 6-membered ring hydrogen bond-containing ODOPB-based benzoxazine in the producing of high-performance thermosetting systems.

Impedance optimization by inserting of flaky Fe3O4/FeS in PANI-derived amorphous carbon for wide band electromagnetic protection

To against the excessive electromagnetic radiation in the current situation, herein the PANI-derived carbon block with flaky Fe3O4/FeS inserted was obtained via a facile route of co-chemical precipitation, low temperature polymerization and vacuum calcination. It discovers that the component of composites and disordered structures in carbon can be regulated by changing the additive amount of iron oxide, and hence the modified electromagnetic parameters to optimize the impedance matching between free air and composites can be achieved as well. On this basis, by optimizing the coupled effect of intrinsic polarizations, conductive dissipation, magnetic resonance and eddy current wastage, the PDC/Fe3O4/FeS composite realizes the efficient microwave absorption within a broad range of 6.55 GHz, covering the entire Ku band for only 2.2 mm thickness of absorber. The work offers a flexible strategy to synthesize desired candidate for broadband electromagnetic protection.

Photo/electro-thermal effect, flame retardant, multifunctional durable superhydrophobic sponge for all-weather recovery high viscosity crude oil and photothermal defrosting/deicing

Developing functional adsorption materials that efficiently adsorb high viscosity oil is crucial for solving oil spill accidents. Herein, low-density three-dimensional porous melamine sponge was used as the modified substrate. First, phytic acid is selected for modification to make it flame retardant. Then, polypyrrole (PPy) and hexadecyltrimethoxysilane (HDTMS) are modified on its surface through low-temperature polymerization and impregnation, ultimately obtaining a multifunctional durable superhydrophobic PA/PPy/HDTMS@MF (melamine foam) sponges with photo/electro-thermal effects and flame retardant. When the applied voltage is 10 V, the core temperature on the PA/PPy/HDTMS@MF sponge’s surface rapidly increases from 26.4 °C to 134.6 °C within 80 s, and the sponge will not burn and be damaged. Under the irradiation of one sunlight (1 kW/m2), the surface core temperature can rapidly rise from 26.4 °C to 93 °C within 70 s. The superhydrophobic PA/PPy/HDTMS@MF sponge can all-weather absorb kinds of high viscosity crude oil and solid oils that are 18–27 times than its own mass, indicating that the prepared superhydrophobic sponge has excellent oil collection performance. And under one sunlight (1 kW/m2), after 10 cycles of desorption, the prepared superhydrophobic sponge can still absorb 26 times more crude oil than its own weight. In addition, PA/PPy/HDTMS@MF sponge also has the characteristic of photothermal defrosting and deicing, and the ice on its surface can begin to melt within 5 min under one sunlight (1 kW/m2). The melted water will not enter the inside of the sponge, effectively ensuring the utilization efficiency of photothermal effects. Based on the above advantages, the prepared photo/electro thermal conversion superhydrophobic sponge has excellent development prospects in the field of high viscosity oil adsorption and photothermal defrosting/deicing.

Greatly recovered electrochemical performances of regenerated graphite anode enabled by an artificial PMMA solid electrolyte interphase layer

Recycling valuable elements, such as Li, Co and Ni, from spent cathode materials, is attracting considerable attention. However, the perspective on the regeneration of spent graphite (SG) anode is still being overlooked. Actually, low-cost recyclization and regeneration are highly feasible due to the intrinsic stable crystal structure of graphite. Herein, a facile sustainable way is proposed to repair the broken surface structure of SG and recover its depressed electrochemical performances. Polymethyl methacrylate (PMMA) is rationally coated onto the SG via a low-temperature polymerization as an artificial solid electrolyte interphase (SEI) layer. The study indicates that the formation of the outer natural SEI layer in the continuous lithiation/delithiation process can be effectively modulated by the inner artificial SEI, which will lead to the formation of a homogeneous bilayer structure. The bilayer SEI configuration can effectively alleviate the decomposition of electrolytes and the loss of the inventory of lithium storage, which is also supported by simulation study. The full cell constructed using regenerated graphite possesses a high capacity of 149 mAh g–1 at 1 C with a retention of 86.7% after 500 cycles. This work provides an economic strategy to regenerate spent graphite anode, paving a way for sustainable battery technology.

Thermo-Responsive Poly(N-isopropylacrylamide)/Hydroxypropylmethyl Cellulose Hydrogel with High Luminous Transmittance and Solar Modulation for Smart Windows.

Thermochromic smart windows are considered to be promising energy-saving devices for reducing energy consumption in buildings. The ideal materials for thermochromic smart windows should have high transmittance, high solar modulation, low phase-transition temperature, and excellent high-temperature thermal stability, which are difficult to achieve simultaneously. This work reports a simple one-step low-temperature polymerization method to prepare a thermo-responsive poly(N-isopropylacrylamide)/hydroxypropylmethyl cellulose (PNIPAM/HPMC) hydrogel achieving the above performances simultaneously. The low-temperature polymerization environment endowed the hydrogel with a high luminous transmittance (Tlum) of 90.82%. HPMC as a functional material effectively enhanced the mechanical properties and thermal stability of the hydrogel. Meanwhile, the PNIPAM/HPMC hydrogel showed a low phase-transition temperature (∼32 °C) and high solar modulation (ΔTsol = 81.52%), which proved that it is an ideal material for thermochromic smart windows. Moreover, a PNIPAM/HPMC smart window exhibited high light transmittance (T380-760 = 86.27%), excellent light modulation (ΔT365 = 74.27%, ΔT380-760 = 86.17%, and ΔT940 = 63.93%), good indoor temperature regulation ability and stability, which indicated that it was an attractive candidate for application in reducing energy consumption in buildings. This work also provides an option and direction for modifying PNIPAM-based thermochromic smart windows.

3D Carbon Nanonetwork Coated Composite Electrode with Multi-Heteroatom Doping for High-Rate Vanadium Redox Flow Batteries.

With the advantages of benign mechanical property, electrochemical stability, and low cost, graphite fibers (GFs) have been widely used as electrodes for vanadium redox flow batteries (VRFBs). However, GFs usually possess inferior electrochemical activity and ion diffusion kinetics for electrode reaction, vastly limiting their application in VRFBs. Here, a 3D carbon nanonetwork coated GFs with multi-heteroatom doping was constructed for application in VRFBs via low temperature polymerization between linear polymer monomer and phytic acid, and subsequent carbonization (900 °C) on the GFs (GF@PCNs-900). Benefiting from the 3D structural features and multi-heteroatom doping (O, N and P), the composite electrode displayed sufficient diffusion of vanadium ions, rapid electron conduction, and highly enhanced electrochemical activity of reactive site on the electrodes. As a result, the GF@PCNs-900 delivered a high discharge capacity of 21 Ah L-1 and energy efficiency of above 70% with extraordinary stability during 200 cycles at 200 mA cm-2. Even at a huge current density of 400 mA cm-2, the GF@PCNs-900 still maintained a discharge capacity of 5.0 Ah L-1, indicating an excellent rate of performance for VRFBs. Such design strategy opens up a clear view for further development of energy storage field.