Microphase-separated Structure Research Articles

Self-Healing Polyurethane Elastomers with Superior Tensile Strength and Elastic Recovery Based on Dynamic Oxime-Carbamate and Hydrogen Bond Interactions.

The preparation of self-healing polyurethane elastomers (PUEs) incorporating dynamic bonds is of considerable practical significance. However, developing a PUE with outstanding mechanical properties and high self-healing efficiency poses a significant challenge. Herein, this work has successfully developed a series of self-healing PUEs with various outstanding properties through rational molecular design. These PUEs incorporate m-xylylene diisocyanate and reversible dimethylglyoxime as hard segment, along with polytetramethylene ether glycol as soft segment. A significant amount of dynamic oxime-carbamate and hydrogen bonds are formed in hard segment. The microphase separated structure of the PUEs enables them to be colorless with a transparency of >90%. Owing to the chemical composition and multiple dynamic interactions, the PUEs are endowed with ultra-high tensile strength of 34.5MPa, satisfactory toughness of 53.9MJ m-3, and great elastic recovery both at low and high strains. The movement of polymer molecular chains and the dynamic reversible interactions render a self-healing efficiency of 101% at 70°C. In addition, this self-healing polyurethane could still maintain high mechanical properties after recycling. This study provides a design strategy for the preparation of a comprehensive polyurethane with superior overall performance, which holds wide application prospects in the fields of flexible displays and solar cells.

Tetramethyl poly(aryl ether ketone) modified by DABCO cationic polymer for high temperature proton exchange membrane fuel cells

Rationally constructing proton transport channel within high temperature proton exchange membranes (HT-PEMs) plays a critical role in lowering the mass transfer resistance and thus improving the performance of HT-PEM fuel cells (HT-PEMFCs). We herein designed a microphase-separated structure to promote proton transmitting by incorporating 1,4-Diazabicyclo[2.2.2]octane (DABCO) cationic polymer into tetramethyl poly(aryl ether ketone) (TMPAEK). The flexible and cationic segments afforded a polarity difference from TMPAEK, resulting in easier phosphoric acid adsorption. High proton conductivity of 135 mS cm−1 was obtained under anhydrous conditions at 150 °C. Besides, the hydrophilic domains that containing N-heterocycle could stabilize phosphoric acid through hydrogen bonding interactions, resulting in high phosphoric acid retention of ∼80 % after 288 h test. A Peak power density of 496 mW cm−2 was achieved in non-humidified H2/O2 without back pressure at 140 °C, which was higher than that of m-PBI under the same conditions. This work not only paved a way to tailor the ion conductivity of membrane, but also provided a highly competitive membrane for HT-PEMFCs.

The effect of polymer with tunable alkyl spacers on the microstructure of amphoteric membrane for vanadium redox flow battery (VRB)

Amphoteric membranes, as promising candidates for VRBs, have attracted more attention. The side-chain-type polymers go far towards improving ion exchange capacity and further enhancing ion conductivity. A kind of Amphoteric ion exchange membranes (AIEMs) with different alkyl chain lengths (C2, C6, and C12 spacers) were synthesized by using ring-opening metathesis polymerization (ROMP). In addition, the interactions between N-containing groups with positively charged and -SO3- groups prevent swelling and vanadium crossover. The microphase separation structure through side chain induction was regulated, to respond to the ionic mobility of the membrane. The effect of the spacer lengths on the ion selectivity of AIEMs is investigated. In addition, the size and matrix of the constructed ion channel were calculated by using coarse-grained molecular dynamics (CGMD) simulation, which further verified the experiment.

Core-Shell Double Gyroids Directed by Selective Solvation for ABC Triblock Terpolymers.

The formation of ABC triblock terpolymers through solution casting is still challenging. In this study, core-shell double gyroid network structures are fabricated via solution casting using poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA) (F)-b-[poly(4-vinylpyridine) (P4VP) (P)]-b-[polystyrene (PS) (S)] (FPS) triblock terpolymers in N,N-dimethylformamide (DMF). Upon heat treatment, the polymer tends to form a sphere-in-lamellar structure at the F/S interface. Given the solubility properties of each component in DMF, it is anticipated that the effective volume fraction of F relative to P would increase in concentrated solutions and the effective volume fraction of S would decrease. The microphase-separated structure derived from the DMF solution consistently results in the formation of a network structure composed of a core-shell double gyroid, with F as the matrix, P as the shell, and S as the core, and their periodic lengths gradually increase to 110.8, 131.8, and 162.7nm as increase molecular weights of PS blocks to 13.8, 20.7, and 28.8kg mol-1. Based on the solubility properties of the polymer components highlighted in this study, the solvent selection strategy is broadly applicable to ABC triblock terpolymers featuring various polymer components, offering a more efficient avenue for fabricating core-shell double gyroid structures.

Mechanically Ultra-Robust Fluorescent Elastomer for Elaborating Auxetic Composite.

Fluorescent elastomers are predominantly fabricated through doping fluorescent components or conjugating chromophores into polymer networks, which often involves detrimental effects on mechanical performance and also makes large-scale production difficult. Inspired by the heteroatom-rich microphase separation structures assisted by intensive hydrogen bonds in natural organisms, an ultra-robust fluorescent polyurethane elastomer is reported, which features a remarkable fracture strength of 87.2MPa with an elongation of 1797%, exceptional toughness of 678.4MJm-3 and intrinsic cyan fluorescence at 445nm. Moreover, the reversible fluorescence variation with temperature could in situ reveal the microphase separation of the elastomer in real time. By taking advantage of mechanical properties, intrinsic fluorescence and hydrogen bonds-promoted interfacial bonding ability, this fluorescent elastomer can be utilized as an auxetic skeleton for the elaboration of an integrated auxetic composite. Compared with the auxetic skeleton alone, the integrated composite shows an improved mechanical performance while maintaining auxetic deformation in a large strain below 185%, and its auxetic process can be visually detected under ultraviolet light by the fluorescence of the auxetic skeleton. The concept of introducing hydrogen-bonded heteroatom-rich microphase separation structures into polymer networks in this work provides a promising approach to developing fluorescent elastomers with exceptional mechanical properties.

Incomplete ionic interactions and hydrogen bonds constructing elastomers with water accelerated Self-Healing and self-healing strengthening capacities

Self-healing polymers with microphase separation structure typically require external stimuli to achieve self-healing, and their performance often degrades. To solve these issues, we introduce tertiary amine and carboxyl groups into polymer. The intermolecular ionic interactions and H-bonds contribute to the formation of microphase separation structures, endowing polyurethane elastomers (PU-n) outstanding mechanical properties with a maximum tensile strength and toughness of 20.61 MPa and 59.02 MJ/m3, respectively. The self-healing of the prepared PU-n can be achieved at room temperature and accelerated significantly by water because hard phases can be dissociated, resulting in enhanced molecular movement. After self-healing with water, the enhanced molecular movement and further ionization of ionic groups lead to stronger H-bonds and ionic interactions, promoting more distinct microphase separation. Thus, the mechanical strength is strengthened and the self-healing efficiency can reach 104.72 %. The enhanced molecular movement and strengthened intermolecular interactions when self-healing with water can also be verified through in-depth analysis of molecular dynamics (MD) simulations of the self-healing process. Furthermore, PU-n display remarkable shape memory and can be recycled through exposure to solvents and hot water. This study provides a novel and general method for preparing materials that can self-heal with water and self-strengthen after self-healing.

Multi-cation alkoxy chains with high ion conductivity and durability in cross-linked poly (aryl piperidinium) anion exchange membranes

AEMs with high ionic conductivity and excellent alkali stability are one of the cores to ensure that AEMWE achieves high performance. For the current problems of AEMs, multi-cation side chain crosslinkers present a mitigation strategy for the inherent “trade-off” between ion conductivity and mechanical strength and ensure exceptional alkali resistance. Herein, we introduced the first report on cross-linked AEMs with several hydrophilic multi-cation alkoxy chains, featuring ethylene oxide (EO). The differentiation in the hydrophilic/hydrophobic microphase separation structures, characterized by varying positions of the alkoxy chains within the three-stage multi-cation crosslinker, was explored by experiments and simulation, as well as bearing on the comprehensive performance of AEMs. Notably, EO located in the middle of multi-cations crosslinker was found to establish a coherent and ordered ion channel. QPTP-NOBN15 AEM exhibited the highest OH− conductivity (166.6 mS cm−1) and demonstrated lower water uptake (44.4 %) and swelling ratio (14.5 %) at 80°C. And meticulously designed cross-linked structures, along with ether-free backbones, bestowed upon QPTP-NOBN15 impressive alkali stability. After being retained in 1 M KOH solutions for 1200 h, ion conductivity of QPTP-NOBN15 remained largely unaffected. Furthermore, QPTP-NOBN15-MEA was evaluated by water electrolysis in 1 M KOH solutions at 60°C and found that the current density reached 1.8 A cm−2 at 2.99 V.

A novel side‐chain type double‐cation grafted poly (binaphthyl triphenyl piperidine) membranes for anion exchange membrane fuel cells

Recent advancements in anion exchange membrane fuel cells (AEMFCs) have been primarily driven by improvements in anion exchange membranes (AEMs). Aryl ether bond‐free membranes have emerged as a promising avenue for enhancing the performance of AEMs. In this study, a novel side‐chain polymer, PBTP‐s‐x, possesses double cationic groups, aiming at further enhancing overall performance for AEMs. The use of a twisted stereospecific backbone structure of polymerized binaphthyl and triple biphenyl monomer and grafted side chains of piperidine cationic groups not only improves the microphase separation structure of the membrane, but also improves the alkali resistance. Notably, the PBTP‐s‐100 AEMs exhibit exceptional OH‐ conductivity, reaching up to 138.21 mS cm‐1, and show outstanding mechanical properties with a tensile strength of up to 28 MPa. Additionally, PBTP‐s‐100 displays excellent durability, proved by the NMR spectral consistency and over 80% ion conductivity retention in 1 M NaOH at 60°C for 4 weeks. And PBTP‐s‐100 exhibits a higher Lowest Unoccupied Molecular Orbital (LUMO) and a larger energy gap for LOMO and Highest Occupied Molecular Orbital (HOMO) by density functional theory calculation, which indicates it possesses sterling alkaline stability. These findings highlight the potential of PBTP‐s‐100 as a highly performing polymer structure suitable for AEM.

Highly Durable Silicone-Based Elastomers Achieved Through the Synergy of Bi-Incompatible Soft Segments and Multi-Scale Hydrogen Bonds.

Developing a silicone elastomer with high strength, exceptional toughness, good crack tolerance, healability, and recyclability, poses significant challenges due to the inherent trade-offs between these properties. Herein, the design of silicone-based elastomers with a nanoscopic microphase separation structure and comprehensive mechanical properties is achieved by combining bi-incompatible soft segments and multi-scale hydrogen bonds. The formation of multi-scale hydrogen bonds involving urethane, urea, and 2-ureido-4[1H]-pyrimidinone (UPy) facilitates efficient reversible crosslinking of the synthesized polymer containing thermodynamically incompatible poly(dimethylsiloxane) (PDMS) and poly(propylene glycol) (PPG). The dynamic dissociation and recombination of hydrogen bonds, coupled with the forced compatibility and spontaneous separation of bi-incompatible soft segments, can effectively dissipate energy, particularly in the crack region during the stretching process. The obtained silicone-based elastomer exhibits a high break strength of 8.0 MPa, good elongation at break of 1910%, ultrahigh toughness of 67.8 MJ m-3, and unprecedented fracture energy of 31.8 kJ m-2 while maintaining their thermal stability, hydrophobicity, healability, and recyclability. This resilient and long-lasting silicone-based elastomer exhibits significant potential for use in flexible electronic devices.

Fluorinated semi-interpenetrating polymer networks for enhancing the mechanical performance and storage stability of polymer-bonded explosives by controlling curing and phase separation rates

Herein, the effect of fluoropolymer binders on the properties of polymer-bonded explosives (PBXs) was comprehensively investigated. To this end, fluorinated semi-interpenetrating polymer networks (semi-IPNs) were prepared using different catalyst amounts (denoted as F23-CLF-30-D). The involved curing and phase separation processes were monitored using Fourier-transform infrared spectroscopy, differential scanning calorimetry, a haze meter and a rheometer. Curing rate constant and activation energy were calculated using a theoretical model and numerical method, respectively. Results revealed that owing to its co-continuous micro-phase separation structure, the F23-CLF-30-D3 semi-IPN exhibited considerably higher tensile strength and elongation at break than pure fluororubber F2314 and the F23-CLF-30-D0 semi-IPN because the phase separation and curing rates matched in the initial stage of curing. An arc Brazilian test revealed that F23-CLF-30-D-based composites used as mock materials for PBXs exhibited excellent mechanical performance and storage stability. Thus, the matched curing and phase separation rates play a crucial role during the fabrication of high-performance semi-IPNs; these factors can be feasibly controlled using an appropriate catalyst amount.

Macromolecular crosslinked poly(aryl piperidinium)-based anion exchange membranes with enhanced ion conduction for water electrolysis

Anion exchange membranes (AEMs) are essential in AEM water electrolysis, providing a cost-effective alternative to proton exchange membranes through the use of noble metal-free electrocatalysts. However, the “trade-off” between conductivity and dimensional stability in AEMs still hinders the development of high-performance water electrolysis. Herein, partially functionalized poly(phenylene oxide) (QPPO) is combined with poly(aryl piperidinium) (QPAP) to fabricate novel crosslinked AEMs (C-QPAP-x-QPPO), addressing the conductivity-stability issue. The crosslinked C-QPAP-x-QPPO AEMs show lower water swelling compared to their non-crosslinked QPAP membrane, mainly due to increased chain entanglements from the crosslinking process. C-QPAP-2-QPPO AEM exhibits a high conductivity of 139.4 mS cm−1 at 80 °C, attributed to the well-defined microphase separation structure. In addition, C-QPAP-2-QPPO AEM demonstrates exceptional alkaline durability, retaining over 86% conductivity and showing slight degradation after 2400 h in 1 M KOH at 60 °C. A water electrolyzer using the C-QPAP-2-QPPO achieves a maximum current density of 1440 mA cm−2 at 80 °C (2.0 V). These findings demonstrate the potential applications of crosslinked C-QPAP-x-QPPO AEMs in electrochemical devices.

Coordinate mechanical property and self‐healing performance by hydrogen bonding promoting microphase separation structures in waterborne polyurethanes

AbstractSelf‐repairing materials aim to replicate nature's repair mechanisms, but their current properties are inadequate for commercialization due to the trade‐off between repair and mechanical properties. An environmentally responsive low‐temperature self‐healing aqueous polyurethane with different sequence structures was developed in which the WPU‐MD/APDS system exhibited excellent performance. Statically, the incorporation of MD (1,8‐diamino‐P‐menthane) enhances hydrogen bonding within the system and facilitates reversible weak dynamic bonding; microphase separation enables aggregation of disulfide bonds in the hard‐phase domain, thereby improving disulfide bond exchange rates. Dynamically, the inclusion of MD introduces a rigid ring structure and promotes microphase separation with increased hydrogen bonding, leading to enhanced mechanical properties of the materials. The material exhibited tensile strength of 27.37 MPa, elongation at break of 1353%, excellent elastic recovery ability, and high tensile toughness of 136 MJ m−3; a sample with thickness of 0.2 mm lifted weight greater than its own weight into 40,000 times without damage recovery at 40°C. Rheological analysis confirmed its self‐healing property at room temperature.

The influence of microphase separation structure of silicon-containing polyurethane on its wear resistance

This study incorporated polydimethylsiloxane (PDMS) and a kind of siloxane-based chain extender (SDO) into polyether urethanes (PEU). The correlation between microphase separation structure and mechanical properties, surface properties and wear resistance were investigated using multiple characterization techniques such as DSC, DMA, SAXS, ATR-FTIR, and XPS. The addition of PDMS significantly reduced the friction coefficient of PEU and enhances the hydrophobicity. The addition of SDO helped to improve the compatibility between PDMS and hard segments of PEU as proved by the fact that the glass transition temperatures of PDMS segments were shifted to higher temperatures and the fraction of loosely hydrogen-bonded carbonyls increased. Due to the improved interfacial adhesion between the immiscible segments, the wear resistance of PEU modified by both PDMS and SDO was obviously enhanced.

High conductivity poly(meta-terphenyl alkylene)s proton exchange membranes for high temperature fuel cell

Phosphoric acid (PA)-doped membranes are regarded as a promising candidate for high temperature proton exchange membranes (HT-PEMs), but the trade-off between mechanical property and conductivity is a major problem limiting their application. Here, two poly(meta-terphenyl alkylene)s (m-TPNs), namely m-TPN-MeIm and m-TPN-TMA, are synthesized by 1-methylimidazole (MeIm) and trimethylamine (TMA) reacting with precursor polymer, respectively. The influence of different cationic groups on the properties of m-TPNs HT-PEMs is investigated in detail. m-TPNs diminish plastication of PA molecules on the mechanical property by separating the adsorption sites for PA molecules from the polymer backbone through long alkyl side chains. As a result, both m-TPN-MeIm and m-TPN-TMA membranes exhibit good mechanical property. Besides, m-TPN-TMA/PA surpasses m-TPN-MeIm/PA in most of aspects owing to the higher ion exchange capacity (IEC) and more distinct microphase separation structure. Noticeably, the proton conductivity of m-TPN-TMA/PA is as high as 0.191 S cm−1 and exhibits excellent stability over a testing time of 100 h at 160 °C thanks to the remarkable acid uptake and microphase separation structure. The m-TPN-TMA/PA-based single cell produces an impressive peak power density of 552 mW cm−2 at 200 °C. Therefore, this work offers a viable alternative for structure design to mitigate the trade-off effect of PA-doped HT-PEMs.

Regulating the microphase separation structure of poly(aryl-alkylene) anion exchange membranes through the spatial structure of the main chain

Improving the microphase separation structure of membranes is considered an effective strategy to solve the trade-off problem, which can increase the conductivity and reduce the swelling. This article designs poly(aryl alkylene) AEMs with different aryl backbone chains (biphenyl, p-terphenyl and m-terphenyl), with the goal of examining the effect of spatial structure main chains on the membrane performance. It is found that the membrane (m-QTPNP) has a better microphase separation structure and a conductivity of 143.5 mS cm−1 (80 °C) via SAXS, TEM and AFM. Due to the lower IEC (2.23 meq g−1), m-QTPNP has a good anti-swelling performance. During tensile testing, the elongation at break of m-QTPNP can reach 105.5% (wet state). Moreover, due to the obvious microphase separation, the attack of OH− on the quaternized groups is reduced, and m-QTPNP has a conductivity retention rate of 95.5% (80 °C, 2 M NaOH, 1560 h). In addition, the peak power density (PPD) of the H2/O2 single cell equipped with m-QTPNP can reach 749 mW cm−2 (80 °C). After 90 h of durability testing, the voltage decayed to 92.2%, with a decay rate of 0.54 mV h−1.

Anion exchange membranes with orderly channels enabled by charge transfer interactions for fast transportation of Cl−

The formation of an ordered microphase separation structure and the realization of efficient selective ion conduction by precise regulation of the self-assembly process of solid ionic conductive polymers are important in the fields of batteries and electrodialysis. To prepare ion exchange membranes with high conductivity and selectivity, we report a strategy for the design of a selective directional self-assembly backbone by the introduction of charge transfer interactions. Fluorescence spectroscopy (FL) and nano-scale microscopy analysis confirmed the self-assembly of the backbone with charge transfer interactions which resulted in good microphase separation structures for fast transportation of Cl−. The obtained QP(NDIB/PyB)-1 anion exchange membrane (AEM) showed the highest chloride ion conductivity of 83 mS cm−1 (80 °C). In addition, the selectivity of QP(NDIB/PyB)-X was verified by separation experiments of Cl− and SO42‐ (PSO42‐Cl‐ = 21.8). This introduction of electron transfer interactions into polymer structures is expected to contribute to the expansion of ion channel construction strategies and the development of ion-exchange membranes.

Development of a deep-learning model for phase-separation structure of diblock copolymer based on self-consistent field analysis

Self-consistent field (SCF) analysis is an indispensable tool for predicting the microphase separation structures of polymer alloys. However, the computation of the phase-separated structures in the equilibrium state is computationally intensive, leading to high costs. To address this challenge, we propose a novel deep learning approach that leverages a generative adversarial network (GAN), a powerful deep generative model, to accelerate SCF analysis. Specifically, we trained the GAN using comprehensive data obtained from SCF analysis, enabling us to generate various images of feasible structures that are similar to the SCF analysis results. Our results demonstrate that the latent variables in the GAN are linked to the physical parameters and features of the phase-separation structures.

Preparation and properties of PPO-based anion exchange membranes with flexible side chains for fuel cells

Poor alkali resistance and low ionic conductivity are the crux of the matter that hinder the commercialization applications of anion exchange membranes (AEMs). Here, we designed and synthesized a range of poly(phenylene oxide) (PPO)-based AEMs with benzyl free side-chain type. After that, the influences of different cationic functional groups, such as quaternary ammonium, imidazole and piperidine, on the membrane performances were examined systemically. The introduction of ether bond-containing side chains to build micro-phase separation structures enhanced the conductivity of AEMs (64 mS·cm−1 at 80 °C). At the same time, the side-chain without benzyl structures effectively avoids the influence of electron withdrawing groups on PPO main chains. Moreover, the steric hindrance effect of the benzene ring can further alleviate the attack of OH−, thereby improving the alkali resistance of the membrane. Molecular dynamics simulations revealed that a well-developed hydrogen bonding network was formed between ether linkages and water molecules in the side-chain structures, which enhanced the electrical conductivity of the membrane. Meanwhile, the prepared membranes owned a good water uptake and a certain dimensional stability. These results provide a basis for the subsequent enhancement of membrane performances.

Novel Fluorinated Anion Exchange Membranes Based on Poly(Pentafluorophenyl-Carbazole) with High Ionic Conductivity and Alkaline Stability for Fuel Cell Applications.

Constructing good microphase separation structures by designing different polymer backbones and ion-conducting groups is an effective strategy for improving the ionic conductivity and chemical stability of anion exchange membranes (AEMs). In this study, a series of AEMs based on the poly(pentafluorophenylcarbazole) backbone grafted with different cationic groups are designed and prepared to construct well-defined microphase separation morphology and improve the trade-off between the properties of AEMs. Highly hydrophobic fluorinated backbone and alkyl spaces enhance phase separation and construct interconnected hydrophilic channels for anion transport. The ionic conductivity of the PC-PF-QA membrane is 123 mS cm-1 at 80°C, and the ionic conductivity of the PC-PF-QA membrane decreased by only 6% after 960h of immersion at 60°C in 1M NaOH aqueous solution. The maximum peak power density of the single cell based on PC-PF-QA is 214mW cm-2 at 60°C.

Constructing high-performance fluoropoly(aryl piperidinium) ion exchange membranes via side-chain engineering for efficient vanadium flow batteries

Vanadium flow batteries (VFBs) have demonstrated significant potential for large-scale energy storage technology. However, the lack of a highly ion-selective and stable ion exchange membrane (IEM) is a major dilemma for developing high-performance VFBs. Herein, we present a new insight to prepare high-performance fluoropoly(aryl piperidinium) IEMs by side-chain engineering modifications. Benefiting from the synergistic effect between the fluorine-containing structure and the functional side chains, distinct microphase-separated structures are formed within the membrane and the prepared IEMs exhibit lower area resistance (0.16–0.41 Ω cm2) compared to Nafion115 (0.57 Ω cm2). The repulsive effect generated by the intrinsic alkaline cation groups inhibits the cross-penetration of vanadium ions, contributing to the ultra-low VO2+ permeability (∼8.63 × 10−9 cm2 min−1, 96 times lower than Nafion115) of the resultant IEMs. Moreover, the unique fluorinated structure effectively suppresses membrane swelling while enabling excellent mechanical and chemical stability. Consequently, the assembled AMPFMP battery achieves excellent efficiency (coulombic efficiency = 99.23% and energy efficiency = 82.15% at a high current density of 200 mA cm−2) and outstanding cycling performance (no significant decay in efficiency during 1000 cycles at 120 mA cm−2), outperforming Nafion 115. These results indicate that the side-chain engineering design of fluorinated IEM provides a valuable strategy for developing efficient and durable VFB diaphragms.