Nanophase-separated Structure Research Articles

Ultra‐Strong and Tough Bio‐Based Polyester Elastomer with Excellent Photothermal Shape Memory Effect and Degradation Performance

AbstractThe exploitation of bio‐based materials derived from renewable resources represents a pivotal strategic approach in addressing environmental pollution and alleviating the scarcity of fossil resources. 2,5‐Furandicarboxylic acid (FDCA) is the most potential substitute for terephthalic acid. Lignin is the most abundant aromatic biomass resource. However, the preparation of high‐performance lignin/FDCA‐based bio‐polyesters remains a formidable challenge. Herein, a multifunctional lignin‐modified polyester elastomer (LFPEe) is designed using FDCA‐based polyester oligomer (PPeF) and lignin (AOH) as building blocks. The LFPEe exhibits superior mechanical properties with the optimum tensile strength, fracture strain, and elastic recovery ratio up to 58.9 MPa, 610% and 88.9%, respectively, attributing to the formation of dual cross‐linking network with nanophase separation structure. Furthermore, leveraging the inherent characteristics of lignin, the LFPEe demonstrates excellent light‐controlled shape memory and excellent UV shielding performance. This innovative work not only breaks the performance dependence of FDCA‐based polyester on high molecular weight but also highlights a novel paradigm for value‐added utilization of lignin in sustainable bio‐polyesters.

Noncovalent Interaction Boosts Performance and Stability of Organic Solar Cells Based on Giant-Molecule Acceptors.

Designing giant-molecule acceptors is deemed as an up-and-coming strategy to construct stable organic solar cells (OSCs) with high performance. Herein, two giant dimeric acceptors, namely, DYV and DYFV, have been designed and synthesized by linking two Y-series derivatives with a vinyl unit. DYFV exhibits more red-shifted absorption, down-shifted energy levels, and enhanced intermolecular packing than DYV because the intramolecular noncovalent interaction (H···F) of DYFV leads to better coplanarity of the backbone. The D18:DYFV film owns a distinct nanofibrous nanophase separation structure, a more dominant face-on orientation, and more balanced carrier mobilities. Therefore, the D18:DYFV OSC achieves a higher photoelectron conversion efficiency of 17.88% and a longer-term stability with a t80 over 45,000 h compared with the D18:DYV device. The study demonstrates that the intramolecular noncovalent interaction is a superior strategy to design giant-molecule acceptors and boost the photovoltaic performance and stability of the OSCs.

Trapping bond exchange phenomenon revealed for off-stoichiometry cross-linking of phase-separated vitrimer-like materials.

Vitrimer materials combined with nano-phase separated structures have attracted attention, expanding the tuning range of physical properties, such as flow and creep properties. We recently demonstrated a preparation of vitrimer-like materials with phase-separated nanodomains in which dissociative bond exchange via trans-N-alkylation of quaternized pyridine was operated. In this study, we demonstrate a new finding about the bond exchange mechanism: that is, the trapping bond exchange phenomenon. The component polymer is a poly(acrylate) containing pyridine side groups randomly along the chain, which is cross-linked by diiodo molecules via pyridine-iodo quaternization, where the quaternized pyridines are aggregated to form nano-size domains. When the cross-linking reaction is performed at an off-stoichiometric pyridine : iodo ratio (i.e., an excess of pyridine groups), free pyridine groups are located in the matrix phase. Since the bond exchange in the present system progresses in an inter-domain manner, the dissociated unit bearing pendant iodo is trapped by the free pyridine groups in the matrix, which generates other small aggregates. This trapping phenomenon greatly affects the relaxation and creep properties, which are very different from those found in conventional knowledge about vitrimer physics.

Construction of multiple crosslinked networks for the preparation of high-performance lignin-containing cellulose nanofiber reinforced polyvinyl alcohol films

Polyvinyl alcohol (PVA) film, a promising alternative to non-biodegradable plastic packaging films for food and medical packaging, is limited by poor water resistance. In this work, a simple solvent evaporation self-assembly was used to construct a nanophase separation structure to establish dense interfacial hydrogen bonding, covalent bonding and iron metal ion coordination interactions between lignin-containing cellulose nanofibers (LCNFs) and PVA matrix to improve the interfacial force and solve the problem of poor compatibility of LCNFs in PVA. The iron ion (Fe3+) coordination tended to combine with the more active lignin phenolic hydroxyl group to construct the nanophase separation structure. Covalent crosslinking of glutaraldehyde (GA) improved the interfacial compatibility of PVA/LCNF films, enhanced the interfacial bonding and formed a homogeneous structure. The multi-nanophase structures improved the strength and elastic modulus of the PVA/LCNF film and provided the films with extremely low water absorption, water vapor transmission rate and excellent UV-shielding. Compared with pure PVA film, PVA-10L-5Fe-3GA film had about 106.9 % higher tensile strength, 93.9 % lower water absorption and 93.4 % lower mass loss, 69.8 % lower water vapor transmission coefficient, and was able to shield UV at 200–400 nm, which is highly expected to be used in packaging films.

Proton transport through interfaces in nanophase-separation of hydrated aquivion membrane: Molecular dynamics simulation approach

We investigate the effect of temperature and hydration on the nanophase-separated structure and proton conductivity in Aquivion and Nafion membranes using molecular dynamics simulation method. By considering two different temperatures (298 and 353 K) and water contents (10 and 20 wt%), our study reveals that Nafion exhibits better nanophase separation and a more mature internal structure of the water phase compared to Aquivion, leading to facilitated proton dissociation and improved proton conduction through vehicular and hopping mechanisms. This study also identifies the formation of a hydronium-mediated bridge configuration that restricts vehicular mobility at low hydration, resulting in a decrease of the vehicular contribution to proton conduction. From quantitative evaluation of the extent of nanophase-separation using structure factor analysis, we find that Nafion has a shorter correlation length with greater concentration contrast in comparison to Aquivion. At high hydration conditions, the hopping mechanism dominates at low temperature while the vehicular mechanism is dominant at high temperature. At low hydration, the vehicular mechanism is significantly decreased due to hydronium-mediated bridge configurations. It is interesting to note that the proton conductivity in the Aquivion membrane is higher despite the Nafion membrane having a higher proton diffusion. We discover that the greater proton conductivity of Aquivion membrane is caused by its higher proton concentration. In general, our findings offer a fundamental knowledge of the connection between nanophase-separated structure and proton transport characteristics in Nafion and Aquivion systems under a range of temperature and hydration circumstances.

Nanophase separated, grafted alternate copolymer styrene-maleic anhydride as an efficient room temperature solid state lithium ion conductor

All solid-state lithium metal batteries (ASSLMBs) based on polymer solid electrolyte and lithium metal anode have attracted much attention due to their high energy density and intrinsic safety. However, the low ionic conductivity at room temperature and poor mechanical properties of the solid polymer electrolyte result in increased polarization and poor cycling stability of the Li metal batteries. In order to improve the ionic conductivity at room temperature while maintaining mechanical strength, we combine the conductivity of short chain polyethylene oxide (PEO) and strength of styrene-maleic anhydride copolymer (SMA) to obtain a grafted block copolymer with nanophase separation structure, which has room temperature ionic conductivity up to 1.14 × 10−4 S/cm and tensile strength up to 1.4 MPa. Li||Li symmetric cell can work stably for more than 1500 h under the condition of 0.1 mA/cm2. Li||LiFePO4 full cells can deliver a high capacity of 151.4 mAh/g at 25 °C and 0.2 C/0.2 C charge/discharge conditions, showing 85.6% capacity retention after 400 cycles. Importantly, the all solid state Li||LiFePO4 pouch cell shows excellent safety performance under different abuse conditions. These results demonstrate that the nanophase separated, grafted alternate copolymer electrolyte has huge potential for application in Li metal batteries.

Low-Frequency Vibrational Density of State of Janus-Polynorbornenes: The Dependence of the Boson Peak on the Nanophase-Separated Structure

Low-Frequency Vibrational Density of State of Janus-Polynorbornenes: The Dependence of the Boson Peak on the Nanophase-Separated Structure

Extremely strengthening fatigue resistance, elastic restorability and thermodynamic stability of a soft transparent self-healing network based on a dynamic molecular confinement-induced bioinspired nanostructure.

Soft self-healing materials are crucial for the development of next-generation wearable electronics that could function in dynamic environments and resist mechanical damage. However, several challenges remain, including fatigue fracture, poor elasticity, and thermodynamic lability, which significantly limit their practical applications. Here, with a model system of soft self-healing polyurea, we propose a molecular engineering strategy of transforming inherently fragile materials with an island-like structure into resilient ones with a bicontinuous nanophase separation structure using 2-ureido-4-pyrimidinone (UPy) supramolecular motifs as structural regulators. The dynamic and continuous hard domains modified by UPy formed a repairable bicontinuous network similar to those of the reticular layer in animal dermis. This design allows for a simultaneous and tremendous improvement in the fatigue threshold (34.8-fold increase), elastic restorability (the maximum elongation for full dimensional recovery increasing from 6 times to 13 times), and thermodynamic stability (4 orders of magnitude improvement in the characteristic flow transition relaxation time), without significantly compromising the compliance, autonomous self-healing, and optical transparency. These mechanical and thermodynamic improvements address current limitations in unfilled soft self-healing materials as reliable substrates for transparent strain-electronics.

Effects of a Nanophase-Separated Structure on Mechanical Properties and Proton Conductivity of Acid-Infiltrated Block Polymer Electrolyte Membranes under Non-Humidification.

Acid-infiltrated block polymer electrolyte membranes adopting a spherical or lamellar nanophase-separated structure were prepared by infiltrating sulfuric acid (H2SO4) into polystyrene-b-poly(4-vinylpyridine)-b-polystyrene (S-P-S) triblock copolymers to investigate the effects of its nanophase-separated structure on mechanical properties and proton conductivities under non-humidification. Lamellae-forming S-P-S/H2SO4 membranes with a continuous hard phase generally exhibited higher tensile strength than sphere-forming S-P-S/H2SO4 membranes with a discontinuous hard phase even if the same amount of Sa was infiltrated into each neat S-P-S film. Meanwhile, the conductivities of lamellae-forming S-P-S/H2SO4 membranes under non-humidification were comparable or superior to those of sphere-forming S-P-S/H2SO4 membranes, even though they were infiltrated by the same weight fraction of H2SO4. This result is attributed to the conductivities of S-P-S/H2SO4 membranes being greatly influenced by the acid/base stoichiometry associated with acid-base complex formation rather than the nanophase-separated structure adopted in the membranes. Namely, there are more free H2SO4 moieties that can release free protons contributing to the conductivity in lamellae-forming S-P-S/H2SO4 membranes than sphere-forming S-P-S/H2SO4, even when the same amount of H2SO4 was infiltrated into the S-P-S.

Pyridine-extended proton sponge enabling high-performance membrane for flow batteries

The development of high-performance and low-cost membrane is of significance towards vanadium flow battery (VFB). The membrane usually suffer from a trade-off challenge between conductivity and selectivity especially in long-term operation of flow battery. Herein, using a proton sponge drived by the proton absorption capacity of extended pyridine groups, a highly ion-selective membrane is fabricated. During acid-assisted doping behaviors, transport nanochannels with highly proton-selective conductivity are constructed based on well-defined nanophase separation structure. The protonated nanochannels display effectively acidic absorption during hydration process for enabling fast proton conduction (a low area resistance of 0.33 Ω cm2) and repelling vanadium ion (a low vanadium ion permeability of 3.04 × 10−10 cm2 s−1). Consequently, prepared membrane with proton sponge exhibits remarkable performance of high energy efficiency of 85.5%, together with excellent chemical durability over 1000 charge-discharge cycles (more than 1100 h) at 120 mA cm−2 in VFB application. These notable properties make prepared membrane as a potential alternative used in large-scale energy storage systems.

Supramolecular interactions enable pseudo-nanophase separation for constructing an ion-transport highway

•A pseudo-nanophase-separation strategy is proposed for constructing an ion-transport highway •“Side chains” are “grafted” onto polymer backbones via supramolecular interactions •Chemical stability issues caused by covalent modifications are circumvented •Supramolecular interactions and underlying mechanisms are clearly elucidated A well-defined hydrophilic/hydrophobic nanophase-separated structure is widely applied for the construction of fast ion-transport pathways in polymeric membranes for energy-related applications such as electrochemical reactors, fuel cells, and redox flow batteries (RFBs). Conventional nanophase separation is induced by covalently grafted side chains, which however complicate membrane preparation and potentially reduce the chemical stability of membranes. In this work, we report a pseudo-nanophase-separation strategy enabled by supramolecular interactions to construct fast and selective ion-transport channels in polymeric membranes. The “side chains” are “grafted” onto the polymer backbone via supramolecular interactions instead of covalent bonds, simplifying the membrane preparation process and simultaneously protecting the polymer backbone from chemical degradation, which is a critical problem usually found in membranes with molecular modifications. The pseudo-nanophase separation enables high-performance membranes for aqueous acidic RFBs, showing high efficiency and good cycling stability, which suggests its potential to design highly conductive and chemically stable membranes for various energy-related devices. A well-defined hydrophilic/hydrophobic nanophase-separated structure is widely applied for the construction of fast ion-transport pathways in polymeric membranes for energy-related applications such as electrochemical reactors, fuel cells, and redox flow batteries (RFBs). Conventional nanophase separation is induced by covalently grafted side chains, which however complicate membrane preparation and potentially reduce the chemical stability of membranes. In this work, we report a pseudo-nanophase-separation strategy enabled by supramolecular interactions to construct fast and selective ion-transport channels in polymeric membranes. The “side chains” are “grafted” onto the polymer backbone via supramolecular interactions instead of covalent bonds, simplifying the membrane preparation process and simultaneously protecting the polymer backbone from chemical degradation, which is a critical problem usually found in membranes with molecular modifications. The pseudo-nanophase separation enables high-performance membranes for aqueous acidic RFBs, showing high efficiency and good cycling stability, which suggests its potential to design highly conductive and chemically stable membranes for various energy-related devices.

H+-Conducting Aromatic Multiblock Copolymer and Blend Membranes and Their Application in PEM Electrolysis.

As an alternative to common perfluorosulfonic acid-based polyelectrolytes, we present the synthesis and characterization of proton exchange membranes based on two different concepts: (i) Covalently bound multiblock-co-ionomers with a nanophase-separated structure exhibit tunable properties depending on hydrophilic and hydrophobic components’ ratios. Here, the blocks were synthesized individually via step-growth polycondensation from either partially fluorinated or sulfonated aromatic monomers. (ii) Ionically crosslinked blend membranes of partially fluorinated polybenzimidazole and pyridine side-chain-modified polysulfones combine the hydrophilic component’s high proton conductivities with high mechanical stability established by the hydrophobic components. In addition to the polymer synthesis, membrane preparation, and thorough characterization of the obtained materials, hydrogen permeability is determined using linear sweep voltammetry. Furthermore, initial in situ tests in a PEM electrolysis cell show promising cell performance, which can be increased by optimizing electrodes with regard to binders for the respective membrane material.

Nanophase Separation in Immiscible Double Network Elastomers Induces Synergetic Strengthening, Toughening, and Fatigue Resistance

High modulus, toughness, and fatigue resistance are usually difficult to be obtained simultaneously in rubbery materials. Here, we report that by superimposing the nanophase separation structure in...

Morphology evolution and thermodynamic behavior of the “soft core hard shell” structure formed by reactive amino triblock in epoxy resin

In this study, a novel triblock copolymer poly(e-caprolactam)-block-poly(dimethylsiloxane)-block-poly(e-caprolactam) (PLC-b-PDMS-b-PLC) was synthesized by ring-opening polymerization. The approach of improving thermal and mechanical properties of thermosetting epoxy resin (ER) used methyl hexahydrophthalic anhydride as hardener and PLC-b-PDMS-b-PLC as modifier. The test results showed the chemical structure and molecular weight of PLC-b-PDMS-b-PLC can be controlled, and PLC-b-PDMS-b-PLC was self-assembled in the epoxy hybrid system to form nanophase separation structure. From the test of thermal and mechanical properties, it can be known that the amount of block in ER will affect the morphology and density of nanophase, thus affecting the toughness of the material. In the “soft-core hard-shell” nanodomain, the interaction of crystalline hard segments and non-crystalline PDMS soft segments overlapped adjacent stress fields, which helped the material absorb energy when subjected to external impact. The fracture toughness and impact strength of the modified resin were increased by up to 1.52 and 2.19 times compared to neat ER, respectively.

Very Strong, Super-Tough, Antibacterial, and Biodegradable Polymeric Materials with Excellent UV-Blocking Performance.

In this work, inspired by the dynamic sacrificial hydrogen bonds in biological materials, a very strong, super-tough, antibacterial, and cost-effective biodegradable poly(vinyl alcohol) (PVA) nanocomposite material was developed by incorporating the nanoscale antibacterial agent TA@LS-Ag. TA@LS-Ag was prepared from the green biomass tannic acid (TA) and sodium lignosulfonate (LS), and was facilely incorporated into the PVA matrix with a homogeneously interspersed nanoparticle size of about 20 nm. The PVA nanocomposite film with 2 wt % addition of TA@LS-Ag achieved the highest specific toughness of 262 J g-1 among the PVA-based films to date, which is far higher than that of natural spider silk (150-190 J g-1 ), as well as a very high tensile strength of 131.6 MPa. The excellent tensile strength and superior toughness were attributed to synergy of the nanophase separation structure and the intense hydrogen-bonding interactions between the nanoparticles and PVA matrix. The PVA/TA@LS-Ag nanocomposite films exhibited good antibacterial properties, despite the extremely low silver content (0.032-0.32 wt ‰). TA@LS-Ag also endowed the PVA films with excellent antioxidant and UV-shielding performance. As the biomass-derived LS and TA and the PVA matrix are all biodegradable, this work offers a facile strategy for preparing high-performance antibacterial and biodegradable polymeric materials.

Imaging the Nanophase-separated Structure of Block Copolymer Thin Film by Atomic Force Microscopy in Aqueous Solution

We employed two modes of atomic force microscopy to characterize the nanophase-separated structure of a block copolymer thin film from poly(2-methacryloyloxyethyl phosphorylcholine) and poly(3-(met...

Synthesis of highly conductive hydrogel with high strength and super toughness

The manufacture of high performance flexible electronic materials remains a huge challenge. Herein, a facile strategy was developed for the preparation of conductive hydrogel with high strength and super toughness using green biomass lignin and biodegradable poly(vinyl alcohol) (PVA) as raw materials. The enzymatic hydrolysis lignin (DEL) was introduced into the PVA hydrogel to form the nanophase separation structure and promote the adsorption of silver ions, which significantly contributed to the improvements in mechanical and conductive properties of the composite hydrogel. The silver ions in the hydrogel were reduced to generate the silver nanoparticles (AgNPs) by immersing in the green reducing agent of sodium citrate solution. The silver nanoparticles in the hydrogel network significantly enhanced the hydrogel, endowing the composite hydrogel Ag0@DEL with particularly large toughness of 78.1 MJ/m3, powerful tensile strength up to 13.3 MPa and high strain at break up to 1220%. The composite hydrogel Ag0@DEL also exhibited good electrical conductivity of about 1.0 S/m and performed high strain sensitivity and stable response to the deformation of stretching, compression and twist.

Sulfonated and Partially Fluorinated Poly(aryl) Multiblock-Co-Ionomer- and Blend Membranes As Proton Conductors for PEM Electrolysis

The core of a PEM water electrolyzer is represented by the proton conductive membrane. While nowadays PFSA-based materials such as Nafion are state of the art in large scale energy applications, there is a strong need for development of cost efficient alternatives, which exhibit reduced gas crossover, high ionic conductivity and durability.Here, we present proton exchange membranes based on two different concepts: Blends of partially fluorinated polybenzimidazole and pyridine side-chain-modified polysulfones (3K-BM) as well as arylene main-chain multiblock co-ionomers (MB-O).The 3K-BM ionomer membranes represent a blend of hydrophilic partially fluorinated and sulfonated aromatic polyethers with two hydrophobic components: F6-PBI and pyridine-modified PSU [1]. Proton conductivity is achieved by the hydrophilic parts of the material whereas the hydrophobic components ensure stability and enable adjustment of mechanical properties.MB-O consists of hydrophobic and hydrophilic building blocks, which are synthesized via step-growth polycondensation. The former blocks are partially fluorinated aromatics, whereas the latter ones are based on sulfonated nonfluorinated aromatics [2].Multiblock-co-ionomers are capable of forming nanophase-separated structures [2,3], which are tunable by varying the ratio of hydrophilic and hydrophobic proportions. In addition to the polymer synthesis and membrane preparation, ex-situ characterization including NMR spectroscopy, gel permeation chromatography, thermogravimetric analysis, H2-crossover analysis via linear-sweep-voltammetry and AC impedance spectroscopy have been performed with our novel materials. First preliminary in-situ tests in a PEM electrolysis cell have already yielded high performances, which can potentially be increased further by optimization of electrodes with respect to binders for the respective membrane material. Acknowledgements This work has been funded by the German Federal Ministry of Education and Research (BMBF) as part of the project: “Increasing Lifespan and Power of Polymer Electrolyte Membrane Electrolysers through High Power Membrane Electrode Assemblies (POWER-MEE)“ References [1] J. Kerres, A. Ullrich, M. Hein, J. Polym. Sci.: Part A: Polym. Chem. 39 (2001) 2874–2888[2] F. Schönberger, J. Kerres, J.Polym. Sci. Part A: Polym. Chem. 45 (2007) 5237–5255.[3] H. Ghassemi, J. E. McGrath, T. A. Zawodzinski, Polymer 47 (2006) 4132-4139

Synthesis and preparation of branched block polybenzimidazole membranes with high proton conductivity and single-cell performance for use in high temperature proton exchange membrane fuel cells

The application of phosphoric acid (PA)-doped polybenzimidazoles (PBIs) in high-temperature proton exchange membrane fuel cells (HTPEMFCs) requires optimal proton conductivity and fuel cell performance. Recently, we found that branched PBIs could absorb more PA due to their large free volume, and block PBIs could yield obvious nanophase-separated structures, both of which were beneficial to proton transportation. Herein, by constructing a branched PBI core block with another derived PBI structure, a novel membrane with a star-shaped, branched block matrix was prepared for the first time. The dendritic polymer backbone with a phase separation path endows the membranes with high PA doping capacity and high-efficiency proton transmission. Noticeably, a high proton conductivity (0.15 S cm−1, 160 °C) and low activation energy (5.6 kJ mol−1) were obtained under anhydrous conditions, and the peak power density of the single-cell test was as high as 713 mW cm−2 at 160 °C. The results indicate that the combination of branching and a block structure is promising for actual use in HTPEMFCs.

Non-destructive fabrication of Nafion/silica composite membrane via swelling-filling modification strategy for high temperature and low humidity PEM fuel cell

Based on the swelling-filling modification strategy, Nafion/silica composite membrane is facilely fabricated by non-destructively filling silica nano-particles into the Nafion framework. High temperature proton conductive performance of modified Nafion membrane is significantly enhanced due to the synergistic effect of maintaining the ordered nanophase-separated structure in Nafion and excellent water retention capacity of the silica fillers. Proton conductivity of the composite membrane is therefore raised to 33 mS/cm at 110 °C and 60% RH, which is enhanced by ca. 30% compared with the pristine Nafion. Taking account into the improved mechanical and oxidative stabilities attributed to the hydrogen bonding interaction between silica nano-particles and Nafion chains, high temperature fuel cell performance is measured and found to be remarkably improved by 37% at low humidity by considering the power density.