Microphase-separated Structure Research Articles

"Fishbone" Design of Amino/N-Spirocyclic Cations toward High-Performance Poly(triphenylene piperidine) Anion-Exchange Membranes for Fuel Cells.

N-Spirocyclic cations have excellent alkali resistance stability, and precise design of the structure of N-spirocyclic anion-exchange membranes (AEMs) improves their comprehensive performance. Here, we design and synthesize high-performance poly(triphenylene piperidine) membranes based on the "fishbone" design of amino/N-spirocyclic cations. The "fishbone" design does not disrupt the overall stabilized conformation but promotes a microphase separation structure, while exerting the synergistic effect of piperidine cations and spirocyclic cations, resulting in a membrane with good conductivity and alkali resistance stability. The hydroxide conductivity of the QPTPip-ASU-X membrane reached up to 133.5 mS cm-1 at 80 °C. The QPTPip-ASU-15 membrane was immersed in a 2 M NaOH solution at 80 °C for 1200 h, and the conductivity was maintained at 91.02%. In addition, the QPTPip-ASU-5 membrane had the highest peak power density of 255 mW cm-2.

Versatile ionic liquid gels formed by dynamic covalent bonding and microphase separated structures

The use of rutin, which combines rigid quercetin-based structural units with flexible glycoside-based structural units, as a crosslinking agent provides a new method for improving the toughness of soft materials.

Dual function of precisely modified hydroxy-PS-b-PMMA as neutral layers and thin films for perpendicularly oriented lamella

We show a facile way to obtain perpendicular lamellae using a block copolymer (BCP) with two hydroxy groups between polystyrene and poly(methyl methacrylate). The BCP works as both neutral layers and thin films with microphase-separated structures.

Enhanced bending electromechanical properties of maleic anhydride-grafted SEBS gels by blending with acrylonitrile-styrene copolymer

The poly(styrene-b-ethylene-co-butylene-b-styrene) (SEBS) gel which a type of electroactive thermoplastic elastomer has significant intrinsic electromechanical coupling effect owing to its unique microphase separated structure. However, the relationship between the structure and electromechanical properties of SEBS gel remains incompletely understood. This study investigates the effects of polar groups and nanostructure parameters on the bending electromechanical property of SEBS gel for improving its bending electromechanical properties, using maleic anhydride-grafted SEBS/white oil (WO) gel (SEBS-M gel) and blends of SEBS-M gel with acrylonitrile-styrene copolymer (SAN). The SEBS-M gel/SAN films exhibited a hexagonally packed cylinder (HEX) morphology, and the radius of polystyrene domains (rPS) as well as the thickness of poly(ethylene-co-butylene) (PEB) domains (dPEB) in the SEBS-M gel/SAN slightly decreased with increasing SAN content up to 15 phr, followed by an increase. The bending displacement and actuation stress of SEBS-M gel/SAN increased with increasing SAN content up to 15 phr. The bending displacement of SEBS-M gel at 1.4 kV is approximately 74 % of that of SEBS gel, while the bending displacement of SEBS-M gel/SAN-15 at 1.4 kV is approximately 195 % and 266 % higher than that of SEBS gel and SEBS-M gel when the SAN content reaches 15 phr, respectively. The grafted maleic anhydride has a counteractive effect on the bending electromechanical properties of SEBS gel, while blending with a certain amount of SAN in SEBS-M gel has a synergistic effect on the bending electromechanical properties of SEBS gel. It is demonstrated that the enchantment of bending electromechanical properties of SEBS gel is achieved not only by adjusting the parameters of its microphase-separated structure but also by inducing segment deformation through electric field-induced dipole orientations.

Low Tg, strongly segregated, ABA triblock copolymers: a rheological and structural study.

ABA triblock copolymers can form microphase separated structures where the B blocks form bridges between A domains, leading to reversible networks interesting for a variety of applications such as pressure sensitive adhesives or thermoplastic elastomers. However, a major drawback of these systems is their rapid loss of mechanical properties upon temperature increase. A potential way to circumvent this limitation would be to design ABA triblock copolymers that keep their microphase separation at high temperatures. In this paper, we report on all-soft ABA triblock copolymers having a poly(n-butyl acrylate) (PnBA) central block and poly(heptafluorobutyl acrylate) (PHFBA) outer blocks. By introducing fluorinated units, the incompatibility between the blocks is largely increased, allowing strong segregation between the block domains, which preserve the microphase separation up to high temperatures despite the low glass transition temperature of the blocks, as shown by temperature dependent SAXS measurements. We study the properties of different copolymers, with similar PHFBA volume fractions but different block lengths. Linear shear rheology measurements revealed the presence of a second, low frequency, plateau whose onset and length depend on the PnBA and PHFBA length, respectively. This plateau also persists up to higher temperatures for longer PHFBA blocks.

Synergistic effect and ionic conductivity of crosslinked imidazole ionic liquids and piperidine cations on poly(biphenyl-piperidine) anion exchange membranes

In order to prepare anion exchange membranes with good performance, and we prepared ether-free bonded poly(biphenyl-piperidine) anion exchange membranes (CQPBP-M-x, x is degree of crosslinking) by introducing cross-linked imidazolium ionic liquids. The introduction of cross-linked imidazolium ionic liquids increases multiple OH− transport sites and establishes a more pronounced microphase-separated structure with the backbone, while acting synergistically with piperidinium cations, resulting in improved membrane conductivity. Meanwhile, the introduction of an ether-free backbone and the construction of a cross-linked structure could promote the chemical stability of the membrane and effectively inhibit membrane swelling. The prepared cross-linked imidazole ionic liquid poly(biphenyl-piperidine) (CQPBP-M-30 %) membrane exhibited relatively good ionic conductivity (88.03 mS/cm), and low swelling (11.75 %) at 80 °C. The H2–O2 fuel cell performance test conducted at 80 °C without back pressure showed a peak power density of 125.7 mW/cm2. Therefore, it is a worthwhile direction to explore to improve the performance of anion exchange membranes by adopting an ether-free backbone and constructing a cross-linked structure contain multiple cationic groups.

Synergistic effects of dry-brush compatibility and shear stress on rapid alignment of lamellar microstructures for block copolymer reflectors

Because of the high viscosity of severe chain entanglements, a time-consuming process of aligning microstructural orientation in high molecular-weight (Mw) block copolymer photonic crystal films imposed limitations on efficient mass production. In this study, the effective alignment of the block copolymer microstructures in the film state can be carried out within approximately a few minutes. This achievement was realized through the synergistic localized compatibility of dry brush and shear stress during the spin-casting process. The orientation and orderliness of the microphase-separated lamellar structure in as-spun poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) films can be meticulously controlled by introducing blends with PS homopolymer (hPS) of varying Mws (Mw,hPS) and cholesteric liquid crystal mesogen (Chol). Within the ternary blended films of hPS/PS-b-P4VP(Chol), the wet-brush miscibility by blending low-Mw hPS with a small molecular weight ratio (α) of Mw,hPS to Mw,bPS (Mw of the PS block chain) of α <1 results in the formation of disoriented lamellar structures, whereas dry-brush localization by introducing high-Mw hPS with α∼0.9 yields highly parallel-aligned lamellar structures to the substrate after spin casting, even with a massive quantity of additive hPS (∼59 wt%). The dry-brush compatibility can be demonstrated by morphological observation in the ternary blended film after extraction of the hPS. As a result, without any further efforts, such as additional solvent or thermal annealing treatments, the as-spun ternary blended film can exhibit visible structural colorations with controlled wavelengths by alternating the quantity of hPS. This provides an accessible solution for rapidly producing flexible photonic crystals featuring tunable photonic band gaps.

Construction and mechanism of phase-locked structured PU elastomers with tunable mechanical and self-healing properties

Self-healing elastomers with great mechanical properties have attracted much attention, however how to balance the mechanical property and self-healing performance is still challenging. In this work, we prepared polyurethane elastomers (PU-n) with different phase-locked structures in which dynamic disulfide bonds and hydrogen bonds are locked at low temperature to provide great mechanical strength and activated by heating to promote self-healing. PU-n exhibit tensile strength from 0.83 MPa to 11.98 MPa because of different microphase separation structures, which is attributed to different thermodynamic compatibility and hydrogen bonds between hard segment with different lengths and soft segment. PU-n can repair surface scratches within 10 min and the well-designed elastomer (PU-50) can achieve a full-cut self-healing efficiency above 90 % at 60 ℃ for 2 h. The self-healing process is dependent on the dynamic recombination of hydrogen bonds and disulfide bonds, which can be accelerated by heating because of the faster molecular motion. The dynamics characteristics of hydrogen bonds and disulfide bonds also endows PU-n with the recyclability, the recycled elastomer exhibits similar mechanical and self-healing properties with original elastomer. This work provides an effective strategy to achieve self-healing polyurethanes with the high mechanical strength.

Microphase separation structures facilitated by dipole molecules and hydrogen bonding in poly (biphenyl piperidine-isatin) anion exchange membranes

The anion exchange membranes (AEMs) have the important function of blocking fuel and conducting OH− to make the cell form a circuit, so its alkali stability directly affects the performance of alkaline fuel cells. Currently, AEMs face a “trade-off” between ionic conductivity and stability. In order to solve this problem, we optimize the alkali resistance and conductivity of AEMs by introducing dipole-interacting side chains and hydrophilic hydroxyl side chains acting simultaneously on a rigid polymer backbone. By adopting the design strategy of “1 + 1>2″, the ion channel efficiency also makes a high-speed leap from a “two-wheeled bicycle” to a “four-wheeled car”. This effective microscopic modulation is clearly demonstrated by transmission electron microscope (TEM), where the AEMs after molecular design carry out a more obvious microphase separation structure at 200 nm. Through the PBP-54-IS- [OPD-100-OH-0] membrane, the maximum ionic conductivity is 100.62 mS cm−1 at 80 °C. After 1000 h at 80 °C, the retention rate of OH− conductivity of all AEMs was over 88.24 %. We also test its fuel cell performance for analysis. When the temperature of the two poles is 75 °C/72 °C, the power density is 147.28 mW cm−2. These are in line with the inherent requirements of AEMs for fuel cell applications.

Architectural control over morphologies of bottlebrush block copolymer superstructures

The morphology of superstructures formed by bottlebrush block copolymers in the melt can be tuned by changing the side chain length or/and their grafting density at constant volume fractions of the blocks. This feature enables fabrication of microphase separated bulk structures and mesoporous materials thereof with spherical or cylindrical domains (precursors of the mesopores), with high porosity unattainable for materials produced from conventional linear block copolymers. These paradigms are proven by DPD simulations that allow constructing morphological phase diagrams of the melt of block copolymers comprising one linear and one bottlebrush block and comparing the simulation results to the predictions of the mean field analytical theory. While the binodal lines separating the stability regions of spherical and cylindrical domains predicted by the theory perfectly match the simulation results, the simulation indicates appearance of a gyroid phase around the theoretical binodal separating the stability ranges of cylinders and lamellae. The results of our work provide guidelines for macromolecular design of novel composite and mesoporous materials with a wide spectrum of potential applications.

Synthesis and Characterization of Side-Chain Liquid-Crystalline Block Copolymers Containing Cyano-Terminated Phenyl Benzoate Moieties

Block copolymers, known for their capacity to undergo microphase separation, spontaneously yield various periodic nanostructures. These precisely controlled nanostructures have attracted considerable interest due to their potential applications in microfabrication templates, conducting films, filter membranes, and other areas. However, it is crucial to acknowledge that microphase-separated structures typically exhibit random alignment, making alignment control a pivotal factor in functional material development. To address this challenge, researchers have explored the use of block copolymers containing liquid-crystalline (LC) polymers, which offer a promising technique for alignment control. The molecular structure and LC behavior of these polymers significantly impact the morphology and alignment of microphase-separated structures. In this study, we synthesized LC diblock copolymers with cyano-terminated phenyl benzoate moieties and evaluated the microphase-separated structures and molecular alignment behaviors. The LC diblock copolymers with a narrow molecular weight distribution were synthesized by atom transfer radical polymerization. Small angle X-ray scattering measurements revealed that the block copolymers exhibit smectic LC phases and form cylinder structures with a lattice period of about 18 nm by microphase separation. The examination of block copolymer films using polarized optical microscopy and polarized UV-visible absorption spectroscopy corroborated that the LC moieties were uniaxially aligned along the alignment treatment direction.

Controlling Microstructure-Transport Interplay in Poly(ether-block-amide) Multiblock Copolymer Gas Separation Membranes.

In this study, we investigated the effect of morphology on the gas-transport properties of a poly(ether-block-amide) (PEBA) multiblock copolymer. We annealed the copolymer samples and varied the annealing temperature to evaluate the influence of changes in the microstructure on the gas transport properties of PEBA. In addition, we used time-resolved attenuated total reflection Fourier transform infrared spectroscopy to evaluate the diffusion coefficient of CO2 in PEBA based on the Fickian model. The effect of the annealing temperature on the microphase-separated structure of the multiblock copolymer is discussed in detail. Furthermore, the gas diffusivity was significantly affected by the purity of the soft domains. The annealed sample demonstrated a 38% increase in CO2 permeability while maintaining a high CO2/N2 permselectivity of approximately 53. The findings of this study provide valuable insight into the design and optimization of PEBA membranes for gas separation applications.

Preparation of low density microcellular thermoplastic polyurethane with high compression properties based on micro-phase separation structure

A new foaming strategy was proposed to prepare microcellular thermoplastic polyurethane (TPU) with high volume expansion ratio, low shrinkage and stable mechanical properties at low temperature by modulating micro-phase separation structure of TPU through the synergistic effect of water as co-blowing agent and polytetrafluoroethylene (PTFE). Molecular dynamics simulation was conducted to screen co-blowing agent (water) interacted well with CO2 and TPU. The interaction of water and CO2 improved the solubility of blowing agents in TPU. The hydrogen bond interaction between water and TPU regulated the arrangement of soft/hard segments and micro-phase separation structure. The volume expansion ratio of microcellular TPU at 100 °C and 15 MPa increased from 4.0 to 9.0 when the water content was 5 wt%. The synergistic effect of water and PTFE improved the regularity of the hard segment. The water and in-situ fibrillated PTFE significantly improved the initial expansion ratio of microcellular TPU and effectively reduced the shrinkage. Eventually, microcellular TPU with 6.5-fold was prepared at 100 °C and its mechanical properties was evaluated.

Pyrrolidinium-functionalized Cardo (TPM) poly(arylene ether sulfone)s membranes for acid recovery: The effects of Cardo (TPM) microstructures

To explore the intrinsic correlation between the rigidity and distortion degree of polymer backbones and the diffusion dialysis (DD) performance of anion exchange membranes (AEMs), pyrrolidinium-functionalized poly(arylene ether sulfone)s containing different Cardo (TPM) moieties were prepared. The structures, properties and DD performance of above AEMs were systematically evaluated. As the Cardo (TPM) group angle increased, the d-spacing, fractional free volume, and membrane area resistance increased, and the microphase separation structures, hydrophilicity, and acid flux decreased, mainly because larger Cardo (TPM) group angles are unfavourable for the close packing of polymer chains in space. Both the Cardo-type and TPM-type AEMs exhibited universal ultrahigh H+/Fe2+ selectivity (S > 3819), which was mainly attributed to the synergistic influence of their rigid narrow ion transport channels, small pore diameter (0.48–0.62 nm) and narrow pore size distribution (0.24–0.68 Å). Additionally, due to the high-density amide groups of TPM units, which decreased the hydrophobicity of the polymer skeleton and induced the formation of an additional transport pathway for Fe2+ through hydrogen bonding interactions, the TPM-type AEMs showed both lower acid flux and selectivity, suggesting that the structure of hydrophilic auxiliary groups should be carefully designed when improving the DD performance of AEMs.

Phase behavior of mixtures of hard colloids and soft coarse-grained macromolecules.

Effective "soft" interactions between macromolecules such as polymers, amphiphilic dendrimers, and suitably designed DNA based dendritic molecules have been shown to be purely repulsive and non-diverging. We report the structure and phase behavior of a mixture of hard colloids and soft coarse-grained macromolecules. Through the use of Reference Interaction Site Model theory and molecular dynamics simulations we find that hard colloids and soft macromolecules act as depletants toward each other, generating a medium-induced effective attraction. This effective attraction leads to the formation of non-dispersed phases at high densities. At low and high fractions of hard colloids the system macrophase separates into two disparate regions of hard colloids and soft macromolecules. However, this system microphase separates into a hard-rich and soft-rich self-assembled domains at intermediate compositions. The formation of microphase separated structure in this system of isotropic, disconnected, and purely repulsive colloids is surprising and quite novel. This behavior is likely due to a softening of the interface between hard-rich and soft-rich self-assembled domains. Molecular dynamics simulations have revealed that the microphase separated state has an overall disordered bicontinuous morphology. The hard-rich domain forms an ordered FCC structure and the soft-rich domain forms a disordered cluster-fluid, making the structure simultaneously ordered and disordered.

Preparation of Strong and Thermally Conductive, Spider Silk-Inspired, Soybean Protein-Based Adhesive for Thermally Conductive Wood-Based Composites.

The development of formaldehyde-free functional wood composite materials through the preparation of strong and multifunctional soybean protein adhesives to replace formaldehyde-based resins is an important research area. However, ensuring the bonding performance of soybean protein adhesive while simultaneously developing thermally conductive adhesive and its corresponding wood composites is challenging. Taking inspiration from the microphase separation structure of spider silk, boron nitride (BN) and soy protein isolate (SPI) were mixed by ball milling to obtain a BN@SPI matrix and combined with the self-synthesized hyperbranched reactive substrates as amorphous region reinforcer and cross-linker triglycidylamine to prepare strong and thermally conductive soybean protein adhesive with cross-linked microphase separation structure. These findings indicate that mechanical ball milling can be employed to strip BN followed by combination with SPI, resulting in a tight bonded interface connection. Subsequently, the adhesive's dry and wet shear strengths increased by 14.3% and 90.5% to 1.83 and 1.05 MPa, respectively. The resultant adhesive also possesses a good thermal conductivity (0.363 W/mK). Impressively, because hot-pressing helps the resultant adhesive to establish a thermal conduction pathway, the thermal conductivity of the resulting wood-based composite is 10 times higher than that of the SPI adhesive, which shows a thermal conductivity similar to that of ceramic tile and has excellent potential for developing biothermal conductivity materials, geothermal floors, and energy storage materials. Moreover, the adhesive possessed effective flame retardancy (limit oxygen index = 36.5%) and mildew resistance (>50 days). This bionic design represents an efficient technique for developing multifunctional biomass adhesives and composites.

PDMS-b-PI-b-PDMS triblock copolymer self-supported membranes with microphase separated structures for efficient ethanol dehydration

High concentration ethanol dehydration had attracted great attentions through membrane separation methodology in the past years, of which membrane is the key factor to decide the separation performance. In this paper, a series of novel self-supported membranes were prepared based on PDMS-b-PI-b-PDMS triblock copolymers by solution casting method. The composition and structure of the copolymers were confirmed by FTIR, GPC and 1HNMR. The self-supported dehydrated membranes showed good thermal, chemical, and mechanical stability. Their water contact angle decreased obviously from 96° to 61° with the increasing PI contents from 50% to 100% in the triblock copolymers. The clear microphase separation with continuous PI domains of PDMS-b-PI-b-PDMS based membranes were observed in the TEM image. The microphase domain size increased with the increasing of molecular weight and content of PDMS. The higher domain size resulted in lower flux and higher separation factor of these membranes. The membrane M3, which has 70 wt% of PI content in the triblock copolymer, exhibit excellent ethanol dehydration performance with flux of 3.96 kg·m−2·h−1, separation factor of 255 and maintained 120 h with barely decreasing in separation performance, for 95 wt% ethanol solution at 20 °C. When elevated the feed temperature upto 60 °C, the dehydration flux increased to 16.90 kg·m−2·h−1, and the separation factor decreased to 37. Membranes with microphase separation have great potential application in the ethanol dehydration.

Proton-blocking tadpole-type anion exchange membranes for acid recovery by electrodialysis

Three kinds of long-side-chain-modified tadpole-type anion exchange membranes (AEMs) named QPEK-DMODAs with microphase separated structures designed for electrodialysis (ED) acid recovery were fabricated from N,N-dimethyloctadecylamine (DMODA) as quaternization agent and poly(arylene ether ketone) (PEK) as skeleton, which is the copolymer of 2,2′,6,6′-tetramethyl biphenol (TMBP) and 4,4′-difluorobenzophenone (DFBP). QPEK-DMODAs were characterized systematically including basic structures and properties, ED recovery performance of H2SO4 solutions without or with metal impurities, and corrosive acid stability. The well-defined microphase separation structure of QPEK-DMODA-3 is formed by the suitable distribution of tadpole ionic groups at the highest IEC of 2.09 mmol g−1. The aggregate structure offers the membrane competent mechanical stability, ion conductivity and permselectivity, as well as low energy consumption and water transport ratio at the ED process. QPEK-DMODA-3 exhibits higher current efficiency (54.58 %) and recovery H+ concentration (1.74 M) than those of QPEK-DMODA-1, QPEK-DMODA-2 and commercial AMX with comparable energy consumption to that of AMX under the ED conditions of Fe2+ absence. Moreover, the Fe2+ removal rate (88.74 %) and ion selectivity (S = 57.32) of QPEK-DMODA-3 are remarkably higher than those of AMX (67.10 % and 17.32) without the scarce of recovery efficiencies in the ED recovery tests of 0.50 M H2SO4 solution containing 0.10 M of Fe2+. The combination of the comparable tolerance to strong acid to that of AMX and the confirmed good ED recovery performances declares a strong potential of tadpole-type QPEK-DMODA-3 in waste acid recovery by electrodialysis.

Ultrahigh tough, self-healing copolymer elastomer crosslinked by reversible imine system

Improvement of toughness is still a challenge for self-healing materials. Most of self-healing materials difficultly balance the mechanical and self-healing property. Here, a molecular design strategy of copolymer is proposed based on three combinations of reversible imine bond, chain motion and thermosensitive hydrogen bond together. The approach initially forms a co-continuous microphase separation structure and then cross-linked by aromatic imine via esterification reaction and Schiff base reaction, which features efficient self-healing, ultrahigh strength and toughness. The resultant elastomer exhibits a high stress at break (≈3 MPa) and high fracture strain (≈600 %). Additionally, the elastomer can reach 95 % self-healing efficiency after healing at 100 °C for 12 h. Extra reversible imine crosslinking displays a doubly promotion for fracture stress, and unchanging strain as well as 1times increase for self-healing efficiency, compared with merely chain motion and hydrogen bonding. This elastomer can be successfully spun into stretchable, conductive, self-healing filaments with core-shell structure by wet spinning and coating methods. It shows excellent corrosion resistance against NaCl, and conductive and self-healing property after coating by PANI polymer. This new type of self-healing polymer is promising to expand the application in future tissue engineering, soft robotics, and biomedical devices.

The effect of high-temperature proton exchange membranes with microphase separation structure on phosphoric acid loss

Phosphoric acid (PA) leakage of PA-doped high-temperature proton exchange membranes (HT-PEMs) is pivotal for its practical application under working conditions. Here, to enhance the PA retention of HT-PEMs, the concept of microphase separation regulated by flexible long aliphatic side-chain was introduced into poly(isatin-co-p-terphenyl-imidazole) matrix (PITI-CmQ90) via direct superacid-catalyzed copolymerization from N-alkylated isatin monomer. The designed PITI-CmQ90 membranes illustrate obvious microphase separation and larger ionic domain confirmed via Small-angle X-ray scattering (SAXS) analysis suggesting wider proton transport channels. Notably, PA/PITI-C6Q90 membrane exhibits the best PA retention ability under relative humidity (RH) cycle tests at different temperatures, which mainly attributed to the excellent PA interaction through moderate ion aggregation in the microphase-separated PEM matrix verified by solid 31P NMR. As a result, the corresponding MEA displays the most durable single-cell performance under a step-V procedure from 1.0 V to 0.1 V cycle experiments at different temperatures. Therefore, the idea of microphase separation structure on PA retention mentioned in this work helps to study the ionic-pairs interactions from the perspective of membrane microstructure and provide a new strategy to enhance the durability of PEMs.