Physical-Entanglements-Supported Polymeric Form Stable Phase Change Materials with Ultrahigh Melting Enthalpy.

With the rapid development of new energy and the upgrading of electronic devices, structurally stable phase change materials (PCMs) have attracted widespread attentions from both academia and industries. Traditional cross-linking, composites, or microencapsulation methods for preparation of form stable PCMs usually sacrifice part of the phase change enthalpy and recyclability. Based on the basic polymer viscoelasticity and crystallization theories, here, a kind of novel recyclable polymeric PCM is developed by simple solution mixing ultrahigh molecular weight of polyethylene oxide (UHMWPEO) with its chemical identical oligomer polyethylene glycol (PEG). Rheological and leakage-proof experiments confirm that, even containing 90% of phase change fraction PEG oligomers, long-term of structure stability of PCMs can be achieved when the molecular weight of UHMWPEO is higher than 7000 kg mol-1 due to their ultralong terminal relaxation time and large number of entanglements per chain. Furthermore, because of the reduced overall entanglement concentration, phase change enthalpy of PCMs can be greatly promoted, even reaching to ≈185 J g-1, which is larger than any PEG-based form stable PCMs in literatures. This work provides a new strategy and mechanism for designing physical-entanglements-supported form stable PCMs with ultrahigh phase change enthalpies.

Polymer Physics behind the Gel-Spinning of UHMWPE Fibers.

Gel-spinning of ultra-high molecular weight polyethylene (UHMWPE) fibers has attracted great interest in academia and industry since its birth and commercialization in the 1980s, due to unique properties such as high modulus, low density, and excellent chemical resistance. However, the high viscosity and long relaxation time greatly complicate processing. In industry, solvents, like decalin and paraffin oil, usually disentangle the physical networks and promote final drawability. From extruding the polymer solution to post-solid-stretching, many polymer physics problems that accompany high-modulus fiber gel-spinning should be understood and addressed. In this review, by detailed discussions about the effect of entanglements and intracrystalline chain dynamics on the mechanical properties of UHMWPE, theoretical descriptions of the structure formation of disentangled UHMWPE crystals, and the origin of high modulus and strength of final fibers are provided. Several physical intrinsic key factors are also discussed, revealing why UHMWPE is an ideal material for producing high-performance fibers.

An Electro-Optical Kerr Device Based on 2D Boron Nitride Liquid Crystals for Solar-Blind Communications.

Achieving light modulation in the spectral range of 200-280 nm is a prerequisite for solar-blind ultraviolet communication, where current technologies are mainly based on the electro-luminescent self-modulation of the ultraviolet source. External light modulation through the electro-birefringence control of liquid crystal (LC) devices has shown success in the visible-to-infrared regions. However, the poor stability of conventional LCs against ultraviolet irradiation and their weak electro-optical response make it challenging to modulate ultraviolet light. Here, an external ultraviolet light modulator is demonstrated using two-dimensional boron nitride LC. It exhibits robust ultraviolet stability and a record-high specific electro-optical Kerr coefficient of 5.1 × 10⁻2 m V-2, being three orders of magnitude higher than those of other known electro-optical media that are transparent (or potentially transparent) in the ultraviolent spectral range. The sensitive response enables fabricating transmissive and stable ultraviolet-C electro-optical Kerr modulators for solar-blind ultraviolet light. An M-ary coding array with high transmission density is also demonstrated for solar-blind ultraviolet communication.

Ozone-Induced Rapid and Green Synthesis of Polydopamine Coatings with High Uniformity and Enhanced Stability.

The development of green, controllable, and simplified pathways for rapid dopamine polymerization holds significant importance in the field of polydopamine (PDA) surface chemistry. In this study, a green strategy is successfully devised to accelerate and control the polymerization of dopamine through the introduction of ozone (O3 ). The findings reveal that ozone serves as an eco-friendly trigger, significantly accelerating the dopamine polymerization process across a broad pH range, spanning from 4.0 to 10.0. Notably, the deposition rate of PDA coatings on a silicon wafer reaches an impressive value of ≈64.8 nm h-1 (pH 8.5), which is 30 times higher than that of traditional air-assisted PDA and comparable to the fastest reported method. Furthermore, ozone exhibits the ability to accelerate dopamine polymerization even under low temperatures. It also enables control over the inhibition-initiation of the polymerization process by regulating the "ON/OFF" mode of the ozone gas. Moreover, the ozone-induced PDA coatings demonstrate exceptional characteristics, including high homogeneity, good hydrophilicity, and remarkable chemical and mechanical stability. Additionally, the ozone-induced PDA coatings can be rapidly and effectively deposited onto a wide range of substrates, particularly those that are adhesion-resistant, such as polytetrafluoroethylene (PTFE).

Stress-Stabilized Crystalline Phases of Ultrahigh Molecular Weight Polyethylene under Tensile Stress.

Ultrahigh molecular weight polyethylene (UHMWPE) is a semicrystalline polymer renowned for its exceptional mechanical properties, making it a popular material in various high-tech fields. Its mechanical attributes are predominantly governed by its crystalline structures, which may experience alterations in the chain conformation and interchain packing during mechanical deformation. This phenomenon leads to the emergence of distinct polymorphs with unique lattice structures. The investigation of stress-stabilized crystal structures of UHMWPE under tensile stress currently poses challenges with certain aspects remaining unclear. To address this, in this study, time-resolved X-ray wide-angle scattering (TR-WAXS) experiments of biaxially stretched UHMWPE films under in situ tensile conditions were conducted. Experimental results revealed two distinct stress-stabilized crystal phases of UHMWPE that differed from those previously reported. These stress-stabilized phases have been identified as the stress-stabilized orthorhombic crystal phase and the stress-stabilized monoclinic crystal phase, and their corresponding lattice parameters have been accurately calculated through an ab initio computational method. These findings provide deeper insights into UHMWPE's behavior under mechanical strain, opening other avenues for further academic exploration and potential applications in cutting-edge fields.

Microstructure and Tensile Properties of Melt-Spun Filaments of Polybutene-1 and Butene-1/Ethylene Copolymer.

Polybutene-1 with form I crystals exhibits excellent creep resistance and environmental stress crack resistance. The filaments of polybutene-1 and its random copolymer with 4 mol% ethylene co-units were produced via extrusion melt spinning, which are expected to be in form I states and show outstanding mechanical properties. The variances in microstructure, crystallization-melting behavior, and mechanical properties between homopolymer and copolymer filaments were analyzed using SEM, SAXS/WAXD, DSC, and tensile tests. The crystallization of form II and subsequent phase transition into form I finished after the melt-spinning process in the copolymer sample while small amounts of form II crystals remained in homopolymer filaments. Surprisingly, copolymer filaments exhibited higher tensile strength and Young's modulus than homopolymer filaments, while the homopolymer films showed better mechanical properties than copolymer films. The high degree of orientation and long fibrous crystals play a critical role in the superior properties of copolymer filaments. The results indicate that the existence of ethylene increases the chain flexibility and benefits the formation of intercrystalline links during spinning, which contributes to an enhancement of mechanical properties. The structure-property correlation of melt-spun PB-1 filaments provides a reference for the development of polymer fibers with excellent creep resistance.

Hybrid Crosslinked Solid Polymer Electrolyte via In-Situ Solidification Enables High-Performance Solid-State Lithium Metal Batteries.

Solid-state lithium-metal batteries constructed by in-situ solidification of cyclic ether are considered to be a critical strategy for the next generation of solid-state batteries with high energy density and safety. However, the poor thermal/electrochemical stability of linear polyethers and severe interfacial reactions limit its further development. Herein, in-situ ring-opening hybrid crosslinked polymerization is proposed for organic/inorganic hybrid polymer electrolyte (HCPE) with superior ionic conductivity of 2.22 × 10-3 S cm-1 at 30 °C, ultrahigh Li+ transference number of 0.88, and wide electrochemical stability window of 5.2 V. These allow highly stable lithium stripping/plating cycling for over 1000 h at 1 mA cm-2 , which also reveal a well-defined interfacial stabilization mechanism. Thus, HCPE endows assembled solid-state lithium-metal batteries with excellent long-cycle performance over 600 cycles at 2 C (25 °C) and superior capacity retention of 92.1%. More importantly, the proposed noncombustible HCPE opens up a new frontier to promote the practical application of high safety and high energy density solid-state batteries via in-situ solidification.

Design and Synthesis of Low Dielectric Poly(aryl ether ketone) from Incorporation Bulky Fluorene Groups and Regular Hydroquinone Structure.

To decrease the dipole polarization rate and reduce the dielectric constant of poly(aryl ether ketone) (PAEK) resin, 1,4-di(4-fluorobenzoyl) cyclohexane (DFBCH), a weakly polarizing cyclohexane-based monomer, was designed and synthesized as the primary reactant. The bulky fluorene group was incorporated to increase the free volume of the resin, further reducing the dielectric constant. Additionally, hydroquinone with a symmetric and regular structure was utilized to enhance the molecular chain's regularity and reduce dipole relaxation, further lowering the resin's dielectric constant and dielectric loss. The PFQEKs series resins exhibited excellent thermal stability with glass transition temperature (Tg) ranging from 222 to 239 °C and 5% weight loss (Td5%) ranging from 458 to 463 °C, with different monomer ratios. As the hydroquinone content increased, the dielectric constant (Dk) and dielectric loss (Df) of the resin decreased significantly, with Dk ranging from 2.92 to 2.77 and Df ranging from 0.011 to 0.008 at 10 GHz.

An Ultrafast, Energy-Efficient Electrochromic and Thermochromic Device for Smart Windows.

Smart windows nowadays undertake the esteemed obligation of reducing energy consumption as well as upgrading living experience. This project aims to devise a smart window that responds to both electricity and heat, with the intention of achieving energy efficiency, privacy preservation, and enhanced decorative attributes. Through the implementation of a novel electrochromic material design, coupled with the optimization of electrochromic devices (ECDs), a high-performance ECD is obtained, demonstrating coloring/bleaching time of 0.53/0.16 s, a transmittance modulation of 78% (from 99% to 21%), and superior performance in six dimensions. Furthermore, temperature-responsive units and an ionic liquid are incorporated into the electrolyte system to create a novel thermochromic gel electrolyte with transmittance modulation from 80% to 0%, and excellent thermal insulation (6.4 °C reduction). Ultimately, an electro- and thermochromic device is developed, featuring an ultrafast color-switching speed of 0.82/0.60 s and multiple working modes. Overall, this work showcases a prospective design pathway for the development of next-generation ultrafast-switching, and energy-efficient intelligent windows.

Strong and Tough Cellulose Hydrogels via Solution Annealing and Dual Cross-Linking.

Strong and tough hydrogels are promising candidates for flexible electronics, biomedical devices, and so on. However, the conflict between improving the mechanical strength and toughness properties of polysaccharide-based hydrogels remains unsolved. Herein, a strategy is proposed to produce a hierarchically structured cellulose hydrogel that combines solution annealing and dual cross-linking treatment approaches. The solution annealing considerably increases the hydrophobic stacking and chemical cross-linking of the cellulose chains, thereby facilitating their subsequent self-assembly and recrystallization during the chemical and physical cross-linking processes. The cellulose hydrogels exhibit superposed chemically and physically cross-linked domains comprising homogeneous nanoporous network structures, which in turn are composed of interconnected cellulose nanofibers and cellulose II crystallite hydrates. These cellulose hydrogels exhibit a high water content of 76-84% and excellent mechanical properties that compare favorably to those of biomacromolecule-based hydrogels. The prepared hydrogels exhibit a mechanical strength and work of fracture of 21 ± 3 MPa and 2.6 ± 0.4 MJ m-3 under compression, and 7.2 ± 0.7 MPa and 5.9 ± 0.6 MJ m-3 under tension, respectively. It is anticipated that this strategy will be applicable to other biomacromolecules and crystalline polymers, and that it will enable the construction of other hydrogels exhibiting high mechanical performances.

Regulating the Coordination Geometry and Oxidation State of Single-Atom Fe Sites for Enhanced Oxygen Reduction Electrocatalysis.

FeNC catalysts demonstrate remarkable activity and stability for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells and Zn-air batteries (ZABs). The local coordination of Fe single atoms in FeNC catalysts strongly impacts ORR activity. Herein, FeNC catalysts containing Fe single atoms sites with FeN3 , FeN4 , and FeN5 coordinations are synthesized by carbonization of Fe-rich polypyrrole precursors. The FeN5 sites possess a higher Fe oxidation state (+2.62) than the FeN3 (+2.23) and FeN4 (+2.47) sites, and higher ORR activity. Density functional theory calculations verify that the FeN5 coordination optimizes the adsorption and desorption of ORR intermediates, dramatically lowering the energy barrier for OH- desorption in the rate-limiting ORR step. A primary ZAB constructed using the FeNC catalyst with FeN5 sites demonstrates state-of-the-art performance (an open circuit potential of 1.629 V, power density of 159 mW cm-2 ). Results confirm an intimate structure-activity relationship between Fe coordination, Fe oxidation state, and ORR activity in FeNC catalysts.

Low-Cost, High-Strength Cellulose-based Quasi-Solid Polymer Electrolyte for Solid-State Lithium-Metal Batteries.

Solid-state lithium-metal batteries are considered as the next generation of high-energy-density batteries. However, their solid electrolytes suffer from low ionic conductivity, poor interface performance, and high production costs, restricting their commercial application. Herein, a low-cost cellulose acetate-based quasi-solid composite polymer electrolyte (C-CLA QPE) was developed with a high Li+ transference number ( t L i + ${{t}_{{{\rm L}{\rm i}}^{+}}}$ ) of 0.85 and excellent interface stability. The prepared LiFePO4 (LFP)|C-CLA QPE|Li batteries exhibited excellent cycle performance with a capacity retention of 97.7 % after 1200 cycles at 1 C and 25 °C. The experimental results and Density Function Theory (DFT) simulation revealed that the partially esterified side groups in the CLA matrix contribute to the migration of Li+ and enhance electrochemical stability. This work provides a promising strategy for fabricating cost-effective, stable polymer electrolytes for solid-state lithium batteries.

Hydrogel/ß-FeOOH-Coated Poly(vinylidene fluoride) Membranes with Superhydrophilicity/Underwater Superoleophobicity Facilely Fabricated via an Aqueous Approach for Multifunctional Applications.

Hydrogel coatings that can endow various substrates with superior properties (e.g., biocompatibility, hydrophilicity, and lubricity) have wide applications in the fields of oil/water separation, antifouling, anti-bioadhesion, etc. Currently, the engineering of multifunctional hydrogel-coated materials with superwettability and water purification property using a simple and sustainable strategy is still largely uninvestigated but has a beneficial effect on the world. Herein, we successfully prepared poly(2-acrylamido-2-methyl-1-propanesulfonic acid) hydrogel/ß-FeOOH-coated poly(vinylidene fluoride) (PVDF/PAMPS/ß-FeOOH) membrane through free-radical polymerization and the in situ mineralization process. In this work, owing to the combination of hydrophilic PAMPS hydrogel coating and ß-FeOOH nanorods anchored onto PVDF membrane, the resultant PVDF/PAMPS/ß-FeOOH membrane achieved outstanding superhydrophilicity/underwater superoleophobicity. Moreover, the membrane not only effectively separated surfactant-stabilized oil/water emulsions, but also possessed a long-term use capacity. In addition, excellent photocatalytic activity against organic pollutants was demonstrated so that the PVDF/PAMPS/ß-FeOOH membrane could be utilized to deal with wastewater. It is envisioned that these hydrogel/ß-FeOOH-coated PVDF membranes have versatile applications in the fields of oil/water separation and wastewater purification.

Non-Coplanar Diphenyl Fluorene and Weakly Polarized Cyclohexyl Can Effectively Improve the Solubility and Reduce the Dielectric Constant of Poly (Aryl Ether Ketone) Resin.

With the rapid development of high-frequency communication and large-scale integrated circuits, insulating dielectric materials require a low dielectric constant and dielectric loss. Poly (aryl ether ketone) resins (PAEK) have garnered considerable attention as an intriguing class of engineering thermoplastics possessing excellent chemical and thermal properties. However, the high permittivity of PAEK becomes an obstacle to its application in the field of high-frequency communication and large-scale integrated circuits. Therefore, reducing the dielectric constant and dielectric loss of PAEK while maintaining its excellent performance is critical to expanding the PAEK applications mentioned above. This study synthesized a series of poly (aryl ether ketone) resins that are low dielectric, highly thermally resistant, and soluble, containing cyclohexyl and diphenyl fluorene. The effects of cyclohexyl contents on the properties of a PAEK resin were studied systematically. The results showed that weakly-polarized cyclohexyl could reduce the molecular polarization of PAEK, resulting in low permittivity and high transmittance. The permittivity of PAEK is 2.95-3.26@10GHz, and the transmittance is 65-85%. In addition, the resin has excellent solubility and can be dissolved in NMP, DMF, DMAc, and other solvents at room temperature. Furthermore, cyclohexyl provided PAEK with excellent thermal properties, including a glass transition temperature of 239-245 °C and a 5% thermogravimetric temperature, under a nitrogen atmosphere of 469-534 °C. This makes it a promising candidate for use in high-frequency communications and large-scale integrated circuits.

Entanglement Characteristic Time from Complex Moduli via i-Rheo GT.

Tassieri et al. have introduced a novel rheological tool called "i-Rheo GT" that allows the evaluation of the frequency-dependent materials' linear viscoelastic properties from a direct Fourier transform of the time-dependent relaxation modulus G(t), without artifacts. They adopted i-Rheo GT to exploit the information embedded in G(t) derived from molecular dynamics simulations of atomistic and quasi-atomistic models, and they estimated the polymers' entanglement characteristic time (τe) from the crossover point of the moduli at intermediate times, which had never been possible before because of the poor fitting performance, at short time scales, of the commonly used generalized Maxwell models. Here, we highlight that the values of τe reported by Tassieri et al. are significantly different (i.e., an order of magnitude smaller) from those reported in the literature, obtained from either experiments or molecular dynamics simulations of different observables. In this work, we demonstrate that consistent values of τe can be achieved if the initial values of G(t), i.e., those governed by the bond-oscillation dynamics, are discarded. These findings have been corroborated by adopting i-Rheo GT to Fourier transform the outcomes of three different molecular dynamics simulations based on the following three models: a dissipative particle dynamics model, a Kremer-Grest model, and an atomistic polyethylene model. Moreover, we have investigated the variations of τe as function of (i) the 'cadence' at which G(t) is evaluated, (ii) the spring constant of the atomic bone, and (iii) the initial value of the shear relaxation modulus G(O). The ensemble of these results confirms the effectiveness of i-Rheo GT and provide new insights into the interpretation of molecular dynamics simulations for a better understanding of polymer dynamics.

Preparation of Nanofiber Bundles via Electrospinning Immiscible Polymer Blend for Oil/Water Separation and Air Filtration.

Nanofiber bundles with specific areas bring a new opportunity for selective adsorption and oil/water or air separation. In this work, nanofiber bundles were prepared by the electrospinning of immiscible polystyrene (PS)/N-trifluoroacetylated polyamide 6 (PA6-TFAA) blends via the introduction of carbon nanotubes (CNTs) or a copolymer of styrene and 3-isopropenyl-α, α'-dimethylbenzene isocyanate (TMI), which was denoted as PS-co-TMI. Herein, CNT was used to increase the conductivity of the precursor for enhancing the stretch of PS droplets under the same electric field, and PS-co-TMI was used as a reactive compatibilizer to improve the compatibility of a PS/PA6-TFAA blend system for promoting the deformation. Those obtained nanofiber bundle membranes showed an increase in tensile strength and high hydrophobicity with a water contact angle of about 145.0 ± 0.5°. Owing to the special structure, the membranes also possessed a high oil adsorption capacity of 31.0 to 61.3 g/g for different oils. Moreover, it exhibits a high potential for gravity-driven oil/water separation. For example, those membranes had above 99% separation efficiency for silicon oil/water and paraffin wax/water. Furthermore, the air filtration efficiency of nanofiber bundle membranes could reach above 96%, which might be two to six times higher than the filtration efficiency of neat PS membranes.

Carbon Nanotubes Grown on the Carbon Fibers to Enhance the Photothermal Conversion toward Solar-Driven Applications.

Photothermal conversion is a directly, sustainable, and green path to use solar energy and the one of the most important keys is the photothermal conversion material. How to obtain the durable and effective material for photothermal conversion with low cost and facile preparation is still a great challenge. In this work, the carbon nanotubes (CNTs) are grown on the carbon fibers (CFs) via the catalysis of trapped Fe and Co. The absorption of the as-prepared CFs/CNTs illustrate the enhancement from the visible light to the near-infrared light range. The photothermal conversion characterization shows the grown CNTs promoting the higher surface temperature and the highest temperature reaches to about 325 °C under 10 sun irradiations. The water evaporation on the CFs/CNTs is measured 1.40 ± 0.03 kg·cm-2·h-1 under 1 sun irradiation and the water evaporation rate is also found depending on the irradiation density. The photothermal conversion applications and the water evaporation under natural irradiation also reveal the suitable candidate of the CFs/CNTs for photothermal conversion application. This work provides a facile path to obtain effective carbon-based materials for photothermal application.

Discussion of Orientation and Performance of Crosslinked Ultrahigh-Molecular-Weight Polyethylene Used for Artificial Joints.

Previously, the orientation structure of ultrahigh-molecular-weight polyethylene (UHMWPE) for artificial joints was considered to be unchanged after irradiation crosslinking. Therefore, much of the research related to the long-term failure of artificial joints has focused on material improvements. In this study, ultrasmall-angle X-ray scattering (USAXS) and the small/wide-angle X-ray scattering (SAXS-WAXS) combined technique reveal that the orientation structures of UHMWPE materials at all scales (nanoscale to microscale) are responsible for the long-term failure of artificial joints. To further illustrate the formation of these hierarchical oriented structures, a simple model is presented. In this model, first, the migration of free radicals plays a vital role, and the different steric hindrances in different directions directly lead to uneven migration behavior of free radicals. Second, the uneven migration of free radicals contributes to an inhomogeneous concentration of free radicals, thus resulting in observable crosslinking nonuniformities. Finally, all the hierarchical structural nonuniformities promote long-term failure of artificial joints after long-term wear.

Study of the Osteoimmunomodulatory Properties of Curcumin-Modified Copper-Bearing Titanium.

Peri-implantitis can lead to implant failure. In this study, curcumin (CUR) was modified onto the copper-bearing titanium alloy (Cu-Ti) with the assistance of polydopamine (PDA) in order to study the bone immune response and subsequent osteogenesis. FE-SEM, XPS and water contact angle were utilized to characterize the coating surface. Bone marrow mesenchymal stem cells (BMSCs) and macrophages were cultured separately and together onto the CUR modified Cu-Ti. Cell activity, expression of relative genes and proteins, cell migration ability, and fluorescence staining of cells were performed. CUR modification slightly increased the activation of M1-type and M2-type cells under physiological conditions. In the inflammation state, CUR inhibited the overexpression of M1 macrophages and induced M2-type differentiation. In addition, the modification itself could provoke the expression of osteoblastic-related genes of BMSCs, while promoting the osteogenic differentiation of BMSCs through the activation of macrophages in both physiological and inflammatory states. The BMSCs migration was increased, the expression of osteogenic-related genes and proteins was up-regulated, and alkaline phosphatase activity (ALP) was increased. Thus, the modification of CUR can promote the osteointegration effect of Cu-Ti by bone immunomodulation and may, in addition, improve the success rate of implants.

Efficient Antibacterial Agent Delivery by Mesoporous Silica Aerogel.

Bacterial infections still cause many health problems for human beings. Silica aerogels with a three-dimensional (3D) porous structure and a large surficial area are promising candidates for drug delivery, but they have rarely been investigated for antibacterial agent delivery. Herein, we study mesoporous silica aerogels as carriers for delivery of three slightly soluble antibacterial agents including cinnamaldehyde (CA, liquid), salicylic acid (SAA, solid), and sorbic acid (SOA, solid) under supercritical fluid carbon dioxide. Notably, all three antibacterial agents form uniform nanocrystals in the mesopores of silica aerogels and the loading efficiency reaches 56 wt %, which assists in overcoming the obstacles of low bioavailability of slightly soluble antibacterial agents. Benefiting from nanocrystallized antibacterial agents, the agent-loaded aerogels exhibit an inhibition rate of 99.99% against Escherichia coli during the initial release; notably, they still have a 95% inhibition rate even after ∼90% of CA is released. Importantly, the agent-loaded silica aerogels demonstrate good biocompatibility in vitro. This work indicates that mesoporous silica aerogels are a promising platform for antibacterial agent delivery.